Die-to-die bonding using copper pillars

EDN: In packaging applications for cellular electronics devices, the use of flip chip copper pillar bumps has been expanding due to its better shape, lesser thickness, smaller form factor, better performance and lower power consumption. Foundries and semiconductor manufacturers are actively evaluating this new technology as the chips are becoming complex and size is shrinking day by day which leads to higher pin count and large interconnect densities which can hamper manufacturability of the bump pad.

Do we really need ternary additives for low-silver alloys?

LinkedIn: Do we really need ternary additives for low-silver alloys?


This 2009 SMTA conference paper appears to show that SAC105 and SAC0307 have surprisingly similar properties to SAC305 without any ternary additives. Comments?
circuitmart.com circuitmart.com
February 28, 2011
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Follow Tim (Indium Corporation)
Tim Jensen • The answer is "it depends." Sure, you can run SAC105 and 0307 successfully and many people are doing that today. However, there are trade-offs when switching to these alloys from SAC305. First of all, low Ag alloys have a higher melting point. In addition, the thermal cycling reliability is not as good as SAC305 (although low Ag alloys do have better drop test performance). The low Ag alloys have a relatively big plastic range (217-227 C) which will hurt the wetting and coalescence.

The addition of dopants to low Ag alloys can help with these issues while still giving the user the cost benefit of less Ag. Every dopant doesn't help will all of these so it is critical for one to determine what characteristics are critical for their application and find the alloy that best meets their needs. SAC105 or 0307 may be the right choice for your application but are probably not ideal for every application.

I have given a number of presentations on alternative alloys to SAC305. I would be happy to share some of that information with interested parties.

Drop Test Performance of BGA Assembly Using SAC105Ti Solder Sphere

IPC: Drop Test Performance of BGA Assembly Using SAC105Ti Solder Sphere


Presentation by Ning-Chen Lee, Ph.D. of Indium Corporation.
 
This presentation was recorded live in San Diego, California during the Technical Conference at IPC APEX EXPO® on February 28, 2012
Total run time of presentation: 30 minutes, 7 seconds

Ning-Cheng Lee, Ph.D., is the Vice President of Technology with Indium Corporation of America. He has been with Indium since 1986. Prior to joining Indium, he was with Morton Chemical and SCM. His more than 20 years of experience includes the development of fluxes and solder pastes for SMT industries in addition to a very extensive background in the development of underfills and adhesives.

Dr. Lee is the author of "Reflow Soldering Processes and Troubleshooting: SMT, BGA, CSP, and Flip Chip Technologies" published by Newnes and co-author of "Electronics Manufacturing with Lead-Free, Halogen-Free, and Conductive-Adhesive Materials" published by McGraw-Hill. He is also the author of a number of book chapters for several lead-free soldering books. He received awards from SMT Magazine in 1991 and 1993; from SMTA for best proceedings papers of SMI or SMTA international conferences in 2001 and from IPC for Honorable Mention Paper – USA at IPC APEX EXPO in 2008. He was honored as a Member of Distinction from SMTA in 2002, with a Lead Free Co-Operation Award from Soldertec in 2003, with an Exceptional Technical Achievement Award from CPMT in 2006, as a Distinguished Lecturer from CPMT in 2007, as a Distinguished Author from SMTA in 2009 and with an Electronics Manufacturing Technology Award from CPMT in 2010.

He currently serves on the SMTA board of directors and has served on the board of governors for CPMT. Among other editorial responsibilities, he serves as a member of an editorial advisory board for Soldering and Surface Mount Technology, Global SMT & Packaging and as associate editor for IEEE Transactions on Electronics Packaging Manufacturing. He has numerous publications to his credit and frequently is invited to make presentations at seminars, give keynote speeches and teach short courses on those subjects at international conferences and symposiums worldwide.

He holds a B.S. in chemistry from National Taiwan University (1973) and earned his Ph.D. in polymer science from the University of Akron (1981).

An Investigation into Low Temperature Tin-bismuth and Tin-bismuth-silver Lead-free Alloy Solder Pastes

IPC: An Investigation into Low Temperature Tin-bismuth and Tin-bismuth-silver Lead-free Alloy Solder Pastes
Presentation by Jasmir Bath of Christopher Associates

This presentation was recorded live in San Diego, California during the Technical Conference at IPC APEX EXPO on February 28, 2012
Total run time of presentation: 17 minutes, 33 seconds

Mr. Jasbir Bath is a Consulting Engineer for Christopher Associates/Koki Solder in the Americas. He is an INEMI Consultant working on the INEMI lead-free rework optimization project.

Bath is also the owner of Bath Technical Consultancy which provides consulting and training services in the electronics manufacturing industry. Previously, he was the Corporate Lead Engineer with Solectron Corporation and Flextronics International for 10 years with a role involving tin-lead and lead-free solder process development.

Influence of laminate type on tin whisker growth in tin-rich lead-free solder alloys

Scopus: This paper describes variations in whisker growth on the surface of tin-rich, lead-free alloys soldered on a Cu layer depending on the laminate used for the printed circuit board, which can be either glass-epoxy or paper-phenol. The structure of the glass-epoxy laminate surface is characterized by spatial nonuniformity caused by the regular structure formed by regions of glass fibers and resin in the top layer of the laminate. The higher value of thermal expansion of the resin than of the glass fiber means that the area of the resin expands more than that of the glass fiber. This causes local compressive stress in the solder layer and as a result promotes whisker growth in the area of the alloy soldered on the Cu layer over the glass fiber. This effect does not occur on the surface of an alloy soldered on Cu layer over a paper-phenol laminate.

Materials Science and Engineering B
2012
Influence of laminate type on tin whisker growth in tin-rich lead-free solder alloys  ( Articles not published yet, but available online Article in press About articles in press (opens in a new window) )

Skwarek, A.a , Pluska, M.b, Czerwinski, A.b, Witek, K.c 

a  Department of Microelectronics, Institute of Electron Technology, Zablocie 39, Cracow, Poland
b  Department of Materials and Semiconductor Structures Research, Institute of Electron Technology, Lotnikow 32/46, Warsaw, Poland
c  Department of Implementation and Production, Institute of Electron Technology, Zablocie 39, Cracow, Poland

Nanoindentation Creep Behavior of Nanocomposite Sn-Ag-Cu Solders

Scopus: High-density, ultrasmall-pitch electronic applications require miniaturized solder bumps with improved thermomechanical performance. In addition, novel techniques which are able to precisely characterize these solder bumps are needed. One approach to meeting both of these requirements is to make use of recently developed nanocomposite solders with enhanced creep resistance, and to characterize these solders using a nanoindentation technique. In the present study, the creep behavior of ceria-reinforced nanocomposite solder foils fabricated by the accumulative roll-bonding process was characterized using a depth-sensing nanoindentation technique. It was found that the creep resistance of the composites increased with increasing volume fraction of CeO 2 reinforcement, and it was deduced that the creep deformation of this nanocomposite proceeded by deformation of the matrix, with the role of the reinforcement being to increase the creep resistance by reducing the effective stress acting on the matrix. The values of the creep exponent suggested that the dominant creep deformation mechanisms involved were diffusion creep and grain boundary sliding.

Journal of Electronic Materials
2012, Pages 1-8
Nanoindentation Creep Behavior of Nanocomposite Sn-Ag-Cu Solders  ( Articles not published yet, but available online Article in press About articles in press (opens in a new window) )

Roshanghias, A.a , Kokabi, A.H.a, Miyashita, Y.b, Mutoh, Y.c, Ihara, I.b, Guan Fatt, R.G.b, Madaah-Hosseini, H.R.a 

a  Department of Materials Science and Engineering, Sharif University of Technology, P.O. Box 11369466, Tehran, Iran
b  Department of Mechanical Engineering, Nagaoka University of Technology, Nagaoka, Japan
c  Department of System Safety, Nagaoka University of Technology, Nagaoka, Japan

Chrys Shea on the Challenges of Lead-Free

Real Time with... IPC APEX EXPO 2012

Video

Chrys Shea discusses the many challenges that lead-free assembly has presented to the electronics industry, including issues from the early days of lead free that were not anticipated: copper dissolution, assembly issues with BTC (bottom side terminations) and pad cratering. Exciting developments in optical inspection are also discussed.

Effects of Zn addition and aging treatment on tensile properties of Sn-Ag-Cu alloys

Scopus: The effects of adding small amounts of Zn and conducting an aging treatment at elevated temperatures on the microstructure and tensile properties of low-Ag Sn-Ag-Cu alloys were investigated. The addition of Zn to Sn-Ag-Cu alloys inhibited the growth of intermetallic compounds. As the amount of Zn increased, the flow stress increased both before and after the aging treatment. In particular, the Sn-1Ag-0.3Cu-1Zn alloy exhibited the highest flow stress among all the examined alloys. Although the flow stress of the Sn-3Ag-0.5Cu alloy was originally higher than that of the Sn-1Ag-0.1Cu-0.4Zn and Sn-1Ag-0.3Cu-0.7Zn alloys, the flow stress of these two alloys was higher after aging for 500 h at 398 K than that of the Sn-3Ag-0.5Cu alloy. The addition of small amounts of Zn in Sn-Ag-Cu alloys suppressed the decline in the flow stress after the aging treatment

Journal of Alloys and Compounds
Volume 527, 25 June 2012, Pages 226-232
Effects of Zn addition and aging treatment on tensile properties of Sn-Ag-Cu alloys

Hamada, N.a , Uesugi, T.b, Takigawa, Y.b, Higashi, K.b 

a  Ishikawa Metal Co., Ltd., Sakai 592-8352, Japan
b  Department of Materials Science, Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531, Japan

Effect of Ni and Bi addition on growth rate of intermetallic compound of SnAgCu soldering

Scopus: The effects of Ni and Bi addition on the intermetallic compound (IMC) growth rate of low-Ag (<1%, mass fraction) Sn-Ag-Cu(LASAC) soldering were investigated by accelerated temperature aging. The thermal fatige resistance of LASAC solders with Ni and Bi addition was studied by comparing with SAC305 solder. The results show that thick Cu 3Sn layer forms after high temperature storage (HTS) aging between LASAC/Cu, LASAC-Bi/Cu and SAC305/Cu interfaces. While the IMC between LASAC-Ni/Cu is (Cu, Ni) 3Sn layer with a very thin thickness after aged. The IMC growth rate of SAC305 is 2.17x10 -5 μm 2/s. However, the IMC growth rate of LASAC solder is 3.810 -5 μm 2/s, which is faster than that of SAC305. The growth rate of IMC at LASAC/Cu interface decreases with Ni and Bi addition. Bi shows a better improvement for solder compared with Ni element. The IMC growth rate of LASAC-Bi is 1.92 x10 -5 μm 2/s, which is slower than the IMC growth rate of SAC305.

Zhongguo Youse Jinshu Xuebao/Chinese Journal of Nonferrous Metals
Volume 22, Issue 2, February 2012, Pages 460-464
Effect of Ni and Bi addition on growth rate of intermetallic compound of SnAgCu soldering

Liu, Y., Sun, F.-L.  

School of Materials Science and Engineering, Harbin University of Science and Technology, Harbin 150040, China

Effects of magnetic fields on microstructure, microhardness and electrochemical corrosion of Sn-9Zn solder

Scopus: The microstructure and property of Sn-9Zn solder were investigated under static magnetic field and rotary magnetic field of 0.125 T by XRD, SEM and electrochemical detector system. The results show that both static magnetic field and rotary magnetic field can refine the microstructure of Sn-9Zn solder, and Zn phase is rotating as well, the microhardness of Sn-9Zn solder under static magnetic field and rotary magnetic field increase by 7.4% and 10.2%, reaching to 18.8 HV and 19.3 HV, respectively, compared with the solder without magnetic field.

While the corrosion potential of the solder under static magnetic field and rotary magnetic field decrease slightly and the corrosion current density obviously declines, which improves the solder corrosion property.

Zhongguo Youse Jinshu Xuebao/Chinese Journal of Nonferrous Metals
Volume 22, Issue 2, February 2012, Pages 485-489
Effects of magnetic fields on microstructure, microhardness and electrochemical corrosion of Sn-9Zn solder

Wu, M.ab , Liu, Z.-J.a 

a  School of Materials Science and Engineering, Shenyang University of Technology, Shenyang 110023, China
b  School of Mechanical Engineering, Liaoning Shihua University, Fushun 113001, China
 

Novel Fe-containing Sn-1Ag-0.5Cu lead-free solder alloy with further enhanced elastic compliance and plastic energy dissipation ability for mobile products

Scopus : This work investigates the effects of small additions (0.1 and 0.3 wt.%) of Fe on the microstructure, mechanical, and thermal properties of the Sn-1Ag-0.5Cu (SAC105) solder alloy. The addition of Fe leads to the formation of large FeSn 2 intermetallic compound (IMC) particles located in the eutectic regions besides the small Ag 3Sn and Cu 6Sn 5 IMC particles. Fe-bearing solders have also been shown to form large primary β-Sn grains. The formation of large FeSn 2 IMC particles, together with the presence of large primary β-Sn grains have resulted in a significant reduction on the elastic modulus and yield strength. Moreover, the presence of large primary β-Sn grains causes the Fe-bearing solders to maintain the total elongation at the SAC105 level. This effect can increase the elastic compliance and plastic energy dissipation ability of the bulk solder, which play an important role in drop impact performance enhancement. The addition of Fe did not produce any significant effect on the melting behavior. As a result, the use conditions of the Fe-bearing solders are consistent with the conditions for conventional Sn-Ag-Cu solder alloys

Microelectronics Reliability
2012
Novel Fe-containing Sn-1Ag-0.5Cu lead-free solder alloy with further enhanced elastic compliance and plastic energy dissipation ability for mobile products  ( Articles not published yet, but available online Article in press About articles in press (opens in a new window) )

Shnawah, D.A.-A.a , Said, S.B.M.b, Sabri, M.F.M.a, Badruddin, I.A.a, Che, F.X.c 

a  Department of Mechanical Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia
b  Department of Electrical Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia
c  Institute of Microelectronics, ASTAR (Agency for Science, Technology and Research), 11 Science Park Road, Singapore Science Park II, Singapore 117685, Singapore

Influence of TiO 2 nanoparticles addition on the microstructural and mechanical properties of Sn0.7Cu nano-composite solder

Scopus: Composites of SC solder reinforced with 0, 0.25, 0.5 and 1wt.% of TiO 2 nanoparticles were fabricated using a mechanical technique. With increased addition of TiO 2 nanoparticles, the SC nano-composite solder was found to have a slightly lower melting temperature. The addition of TiO 2 nanoparticles can also effectively refine the microstructure as so β-Sn and Cu 6Sn 5, and increase the percentage of eutectic area. The mechanical properties (microhardness, 0.2% YS and UTS) increase with the increasing presence of reinforcement, far exceeding the strength of the eutectic SC solder. The yield strength improvement was attributed to (i) the Hall-Petch effect due to β-Sn grain size refinement. (ii) Orowan strengthening, (iii) generation of geometrically necessary dislocations to accommodate CTE mismatch between the matrix and the second phase (Cu 6Sn 5 and TiO 2), and (iv) the load-bearing effects due to the presence of nano-sized reinforcements.

Materials Science and Engineering A
Volume 545, 30 May 2012, Pages 194-200
Influence of TiO 2 nanoparticles addition on the microstructural and mechanical properties of Sn0.7Cu nano-composite solder

Tsao, L.C.a , Huang, C.H.b, Chung, C.H.a, Chen, R.S.b 

a  Graduate Institute of Materials Engineering, National Pingtung University of Science and Technology, 1, Hseuhfu Road, Neipu, Pingtung 91201, Taiwan
b  Department of Engineering Science, National Cheng-Kung University, 1, University Road, Tainan City 701, Taiwan

The effect of indium and bismuth addition on IMC formation of SN 96AG 3.5CU 0.5 solder

Scopus: This work focused on the effect of adding indium and bismuth to wettability and the IMCs that form at the surface before and after aging to the ternary Sn 96Ag 3.5Cu 0.5 solder. Solders (SAC-9In and SAC- 5In4Bi) were prepared by melting the components together at 500'C. Solders were then re-flowed on Cu substrate at temperature 20'C and 40'C above melting point for each solder. The microstructural characteristics of IMCs formed at solder joint before and after aging were carried out using Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-Ray (EDX). The DSC result shows that the melting point of SAC solder was reduced from 217'C to 202'C and 214'C with addition of 9% In and 4% Bi respectively. Adding In increases F max and lower wetting time and thus indicates better wettability. Addition of Bi results in lower thickness of IMC and this indicates better reliability of solder joint.

Malaysian Journal of Microscopy
Volume 7, Issue 1, 2011, Pages 14-19
The effect of indium and bismuth addition on IMC formation of SN 96AG 3.5CU 0.5 solder

Abdul Karim, A.W., Nurulakmal, M.S.  

School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, 14300 Seberang Perai Selatan, Nibong Tebal, Penang, Malaysia

Nihon Superior President to Participate in NEPCON China Reflow Optimization Roundtable

EMSNow Nihon Superior has announced that its President Tetsuro Nishimura has been invited to participate in a Roundtable discussion, "Optimizing Reflow of Lead-Free Boards and BGAs," hosted by EMSNow. This Roundtable will take place at 3.30 p.m. on April 26, 2012 at the NEPCON China exhibition being held in the Shanghai World Expo Exhibition & Convention Center.

Issues to be covered in this discussion on best practice in lead-free reflow include optimization of thermal profiles for the assembly of consumer, industrial and high-reliability aerospace and military electronics. Discussions will extend to other issues that can affect the reliability of lead-free electronics such as tin whiskers.

Tin and silver - the new electric metals

Canadian Mining Journal: And he forecasts major tin shortages by 2018

“We found that even with all the projects that we could identify globally that desire to come to market by then, the world will be in tin shortfall,” he concludes. “At that point we have a serious problem with respect to tin supply. We have a serious problem with respect to the provisioning of solders that will meet RoHS requirements. We have a serious problem getting our iPads and our iPhones. And this is an interesting dilemma.”

Recent discussions with one solder company confirmed Hykawy’s suspicions that the electronics industry isn’t prepared for the impending tin shortages. The company admitted that there were issues with future tin supply but said they were looking into substituting tin with materials like bismuth. When Hykawy told the company that production of bismuth was 1,500 tonnes per year compared with 150,000 tonnes of tin, and that bismuth was only marginally less toxic than arsenic, the response was that they "were working on it."

“Tin and silver and especially tin are likely to come into shorter and shorter supply and that’s going to put a squeeze on prices in the near term [and] it’s going to be potentially disruptive in the longer term,” he cautions. “The reasons that we’re going to have higher prices is that most of the really good deposits are gone. We have been mining tin and silver for a very, very long time. And the best grades, the easiest deposits to find, the most metallurgically amenable deposits — our grandparents and our great grandparents got those.”

IPC Technology trends study reveals changes in store for pCB fabricators and suppliers

EMSNow: IPC"s PCB technology trends study was conducted in late 2011 in English and Chinese. Forty-one PCB manufacturing companies participated, including many of the leading companies in Asia, Europe and North America. They represent 16.5 percent of the world PCB market. The IPC study sample is representative of the global industry in terms of company size and product mix.

Between 2011 and 2014, high-density interconnect (HDI) board production is expected to grow 26 percent for the companies that participated in IPC"s PCB Technology Trends study. They also anticipate greater use of stacked and staggered microvias, leading to any-layer microvias and "via anywhere" capability. While miniaturization and the demands of high-speed technology are driving these trends, companies cite solder mask registration and assembly as the two most common factors limiting the miniaturization of circuitry dimensions.

Most of the companies are evaluating new surface finishes, especially electroless nickel, immersion palladium and immersion gold (ENIPIG). The report also confirms that the high price of gold is having an impact on changes in PCB processing, with nearly one-quarter of the participants trying alternative metals. Seventeen percent of respondents are trying to use reduced thicknesses of gold, including some who claim that the price of gold is having no impact on their material selection.

Of the two primary substrate materials used today, multi-function epoxy resin is expected to grow to be used in more than half of panel area produced by 2014, while the use of glass fabric is expected to decline. Companies" data on laminates used today along with forecasts for 2014 show laminates moving toward higher-temperatures thermal properties. They also predict the use of more low-loss materials. It is expected that by 2014 nearly half of the panel area produced will be halogen free and nearly three-quarters will be lead free.

The industry anticipates significant increases in the production of hybrids or modules, and in the use of printed electronics and optical technology in producing printed boards by 2014.

PCB Technology Trends 2011 is available free to companies that participated in the survey. Other companies may purchase the report by visiting IPC"s online store at www.ipc.org/pcb-tech-trends-2011. The price for IPC members is $675 and the standard price is $1350. The report will also be published in Chinese next month.

Solder joint reliability of SnAgCu solder refinished components under temperature cycling test

Scopus: SnAgCu (SAC) solder is being offered as a lead-free termination finish. SAC finish is obtained by dipping the terminals of components into molten SAC solder. However, the reliability of solder joints formed with SAC solder refinished components needs to be determined in order to evaluate the effects of the SAC solder refinishing process. In this paper, the strength of solder joints with SAC solder refinished thin small outline packages (TSOPs) was evaluated by the shear test. The reliability of solder joints formed with SAC solder refinished components, including TSOPs and resistors, was evaluated by a temperature cycling test. Original Sn finished components were used as a baseline for comparison.

It was found that SAC solder refinishing increased solder joint strength. SAC solder refinishing decreased the fatigue life of solder joints of TSOPs and increased the fatigue life of resistors under temperature cycling conditions

IEEE Transactions on Components, Packaging and Manufacturing Technology
Volume 1, Issue 5, May 2011, Article number 5756459, Pages 798-808
Solder joint reliability of SnAgCu solder refinished components under temperature cycling test

Wang, W.ab , Osterman, M.a , Das, D.a , Pecht, M.cd  

a  Center for Advanced Life Cycle Engineering, University of Maryland, College Park, MD 20742, United States
b  Baker Hughes Inc., Houston, TX 7721-4740, United States
c  Department of Electronics Engineering, City University of Hong Kong, Hong Kong, Hong Kong
d  Electronic Products and Systems Consortium, Center for Advanced Life Cycle Engineering, University of Maryland, College Park, MD 20742, United States

Thermal cycling ramifications of lead-free solder on the electronic assembly repair process

Scopus: The conversion from tin-lead to lead-free electronics has created concern amongst engineers about the reliability of electronic assemblies and the ramifications that reliability changes may have on the life cycle cost and availability of critical systems that use lead-free electronics.

In order to analyze the impact of the tin-lead to lead-free electronics conversion in terms of life cycle cost and availability, a simulation of fielded electronic systems to and through a board-level repair facility was created. Systems manufactured with tin-lead parts or lead-free parts that are fielded, fail and have to be repaired are modeled. The model includes the effects of a finite repair process capacity, repair prioritization, multiple possible failure mechanisms, no-fault-founds, and un-repairable units. The model is used to quantify and demonstrate the system-and enterprise-level risks posed by the conversion from tin-lead to lead-free electronics. Example analyses were performed on electronic assemblies that use SAC (tin, silver and copper) and tin-lead solder using a repair process modeled after a NSWC Crane Aviation Repair Process (8000 assemblies with 30 year support lives were modeled). The components considered consisted of ball grid array, column grid array and leadless chip carrier packaged parts that experienced three different thermal cycling profiles.

The case studies revealed that when exposed to usage profiles characteristic of consumer electronics, low maximum and mean thermal cycling temperatures with long dwell times, SAC exhibited significantly reduced repair costs compared to tin-lead. For usage profiles characteristic of aerospace and high-performance applications, high maximum and mean thermal cycling temperatures with short dwell times, SAC exhibited significantly increased repair costs when compared to tin-lead.

IEEE Transactions on Components, Packaging and Manufacturing Technology
Volume 1, Issue 6, June 2011, Article number 5784324, Pages 964-974
Thermal cycling ramifications of lead-free solder on the electronic assembly repair process

Chaloupka, A.C. , Sandborn, P.A. , Konoza, A.  

Department of Mechanical Engineering, Center for Advanced Life Cycle Engineering Electronics Products and Systems, University of Maryland, College Park, MD 20742, United States

Assessment of solder-dipping as a tin whisker mitigation strategy

Scopus: Tin whiskers have been brought back into the spotlight due to the transition of the electronics industry to lead-free solders. Many different tin whisker failure mitigation strategies are being evaluated by researchers. This paper investigates the technique of solder-dipping as a tin whisker mitigation strategy for tin-based lead-free finished surfaces used in electronic products. Tin finished Alloy 42 lead-frame parts are subjected to the solder-dip process. For this paper, the solders included eutectic tin-lead and tin-silver-copper. In addition, tin-bismuth (Sn-Bi) finished alloy 42 lead-frame parts are also examined to assess the effectiveness of the Sn-Bi finish in mitigating tin whisker growth. Parts under study are subjected to temperature cycling conditions to promote whisker formation.

It is observed that whiskers are formed on all treatment surfaces, with the longest whiskers occurring on the pure tin-finished parts. The solder-dipped parts showed better mitigation of tin whiskers than the pure tin-finished parts.

IEEE Transactions on Components, Packaging and Manufacturing Technology
Volume 1, Issue 6, June 2011, Article number 5765487, Pages 957-963
Assessment of solder-dipping as a tin whisker mitigation strategy

Mathew, S.a , Wang, W.ab , Osterman, M.a , Pecht, M.a  

a  Center for Advanced Life Cycle Engineering, University of Maryland, College Park, MD 20742, United States
b  Baker Hughes Inc., Houston, TX 77019-2182, United States

Brittle versus ductile failure of a lead-free single solder joint specimen under intermediate strain rate

Scopus: The failure mode of Sn-4.0Ag-0.5Cu solder joints under the intermediate strain rates is explored. Tensile and shear tests were performed on miniature solder joints at two different displacement rates, i.e., 5 and 50 mm/s. For the uniaxial tensile test, brittle failure occurred at the intermetallic compound (IMC)/Cu pad interface on the board side under both loading rates. However, for shear loading at 5 mm/s, ductile failure along the solder matrix was detected. With the increase of the shear loading rate up to 50 mm/s, the failure mode is converted into the (ductile brittle) mixed mode.

Numerical simulation results based on the extracted elastic-plastic solder properties indicate that the maximum stress concentration is located at the interfaces of the board side, which indicates the weak position of the crack initiation. The plastic deformation of the solder alloy is significantly suppressed at 50 mm/s loading rate. The amplitude of the solder plastic deformation under shear loading is much greater than that for the tensile test. Furthermore, most plastic deformation under shear loading is in the solder alloy adjacent to solder/IMC interface of the board side and no visible plastic deformation is detected in the middle of solder ball, which results in cohesive failure at the rate of 5 mm/s and the (ductile brittle) mixed failure mode at the rate of 50 mm/s

IEEE Transactions on Components, Packaging and Manufacturing Technology
Volume 1, Issue 9, September 2011, Article number 5997301, Pages 1456-1464
Brittle versus ductile failure of a lead-free single solder joint specimen under intermediate strain rate

Jing, J.a , Gao, F.bc , Johnson, J.bd , Liang, F.Z.e , Williams, R.L.e , Qu, J.bc  

a  State Key Laboratory of Mechanical Systems and Vibration, Shanghai JiaoTong University, Shanghai 200000, China
b  George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, United States
c  McCormick School of Engineering and Applied Science, Northwestern University, Evanston, IL 60208, United States
d  Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, MA 02421-6426, United States
e  Intel Corporation, Hillsboro, OR 97124, United States

PCB Technology Trends 2011

PCB Technology Trends 2011: This global study of technology trends in the PCB industry is based on an extensive survey in which 41 leading PCB companies from all regions of the world participated. It covers issues in PCB technology today and expectations for developments through 2014. Topics include trends in high-density interconnect (HDI) and microvias, miniaturization in PCB production, solder mask, final finishes, metals, substrate materials, laminates, embedded technology, printed electronics, optics and manufacturing equipment. Sales growth drivers, the impact on sourcing, technical challenges and unmet technology needs are also explored.

Spherical solder reflow method for making solder balls

US8162203: Various technologies exist for depositing solder bumps on to IC devices at the wafer level, including, for example, evaporation, electroplating, screen-printing, jetting, ball dropping, and Controlled Collapse Chip Connect New Process (i.e., C4NP) These deposition methods are often referred to as solder wafer bumping or C4 wafer bumping. Originally, solder wafer bumping was accomplished by evaporating both the ball-limiting metallurgy (BLM) and solder through mask holes in an array fashion onto the wafer surface. As the demand for higher I/O density, and lower cost of flip-chip interconnections has increased, however, other deposition methods have been developed. For example, ball drop methods, used to make micro-size solder balls, have recently gained attention in the industry because these methods allow for flexibility in the solder alloys used and finer pitch applications. Indeed, in U.S. Pat. No. 6,517,602, Sato et al. disclose a method of forming solder balls by using a droplet spraying method. This method enables production of micro-sized solder balls, but does not enable formation of solder balls having diameters less than 50 microns due to nozzle-size limitations. Furthermore, the process described by Sato et al. does not produce uniform solder balls, and thus a secondary sorting process is needed to obtain solder balls of the same size.
    More recently, injection molded solder (IMS) processing has been used as a cost-effective solder wafer bumping method. While solder balls formed by IMS are usually more uniform in size than those produced by “ball drop” techniques, the uniformity of the solder balls can be lost if the solder balls escape from the mold plate and are allowed to merge with one another after reflowing occurs. Therefore, it would be desirable to develop an IMS process wherein merging or bridging of the solder balls is reduced or prevented.
SUMMARY OF THE DISCLOSURE
    The present disclosure provides IMS methods that reduce and/or prevent bridging of two or more solder balls during reflow of the solder. The IMS methods of the instant disclosure provide cost-effective processes of making two or more solder balls that are uniform in size.
    A first aspect of the present disclosure is a method of preventing or reducing bridging of two or more solder balls during an injection molded soldering process comprising:


US United States of America

   
Inventor:     Gruber, Peter A.; Mohegan Lake, NY, United States of America
Nah, Jae-Woong; New York, NY, United States of America

Assignee:     International Business Machines Corporation, Armonk, NY, United States of America
other patents from INTERNATIONAL BUSINESS MACHINES CORPORATION (280070) (approx. 44,393)
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Published / Filed:     2012-04-24 / 2011-02-18

Application Number:     US2011000030594

IPC Code:     Advanced: B23K 31/02;

U.S. Class:     228/256; 228/180.22; 228/246; 228/260;

Field of Search:     Non/00e

Priority Number:    
2011-02-18      US2011000030594

Modeling high temperature reliability of flip chip Pb-free solder joint at varying bond pad diameter

Scopus: The flip chip (FC) assembly of die on a substrate has been in existence since the 1960's and it is currently poised to be the strategic technology for actualization of miniaturization trends in electronic packaging. However, due to increase in application of electronic devices to sectors where operating conditions are very harsh and demanding very high safety, FC assembly reliability has become a critical concern. This paper discusses results of a modeling study focused on determination of contribution of variation of printed circuit board (PCB) bond pad diameter on structural static stability of FC48D6.3C457 interconnects at high temperature excursion. The result analysis is based on accumulation of damage indicators such as stress, strain and plastic work in the solder joints. The accumulated damage was used to predict the life of different architecture of the FC. Findings of this work will be of interest to high temperature electronics (HTE) reliability engineers.

AES-ATEMA International Conference Series - Advances and Trends in Engineering Materials and their Applications
2011, Pages 385-393
9th International Conference on Advances and Trends in Engineering Materials and their Applications, AES-ATEMA'2011;Montreal, QC;1 August 2011through5 August 2011;Code89381
Modeling high temperature reliability of flip chip Pb-free solder joint at varying bond pad diameter  ( Conference Paper )

Amalu, E.H.a , Ekere, N.N.a , Aminu, G.b  


a  Electronics Manufacturing Engineering Research Group, School of Engineering at Medway, University of Greenwich, Chatham Maritime, Kent, ME4 4TB, United Kingdom
b  Petroleum Technology Development Fund (PTDF), Port Harcourt Crescent, Area 11, Garki, Abuja, Nigeria

Reliability behavior of lead-free solder joints in electronic components - Review

Scopus - Document details: With more consumer products moving towards environmentally friendly packaging, making solder Pb-free has become an urgent task for electronics assemblies. Solder joints are responsible for both electrical and mechanical connections. Solder joint does not have adequate ductility to ensure the repeated relative displacements due to the mismatch between expansion coefficients of the chip carrier and the circuit board. Materials behavior of solder joints involves a creep-fatigue interaction, making it a poor material for mechanical connections. The reliability of solder joints of electronics components has been found playing a more important role in service for microelectronics components and micro-electro-mechanical systems. So many researchers in the world investigated reliability of solder joints based on finite element simulation and experiments about the electronics devices, such as CR, QFP, QFN, PLCC, BGA, CSP, FCBGA and CCGA, which were reviewed systematically and extensively. Synchronously the investigation on reliability of solder joints was improved further with the high-speed development of lead-free electronic packaging, especially the constitutive equations and the fatigue life prediction equations.

In this paper, the application and research status of constitutive equations and fatigue life prediction equations were reviewed, which provide theoretic guide for the reliability of lead-free solder joints

 Journal of Materials Science: Materials in Electronics
2012, Pages 1-19
Reliability behavior of lead-free solder joints in electronic components  ( Articles not published yet, but available online Article in press About articles in press (opens in a new window) )

Zhang, L.ab , Han, J.-g.a, He, C.-w.a, Guo, Y.-h.a

a  School of Mechanical and Electrical Engineering, Jiangsu Normal University, Xuzhou, 221116, China
b  Provincial Key Laboratory of Advanced Welding, Jiangsu University of Science and Technology, Zhenjiang, 212003, China

Electrically conductive polymer compositions containing metal particles and a graphene and methods for production and use thereof

Espacenet: Polymer compositions containing a polymer matrix, a graphene that is covalently bonded to the polymer matrix and metal particles are described herein. A combined concentration of the metal particles and the graphene in the polymer matrix exceeds an electrical percolation threshold. In general, the graphene has a carbon:oxygen ratio of at least about 20:1 so as to impart a high electrical conductivity thereto. The polymer compositions can be used as a lead-free solder material, in which case they can allow multiple rework operations to take place at a connection. Methods for making and using such electrically conductive polymer compositions are also described.


Page bookmark     US8167190  (B1)  -  Electrically conductive polymer compositions containing metal particles and a graphene and methods for production and use thereof
Inventor(s):     BULLOCK STEVEN [US]; VANDERWIEL ROBERT W [US] +
Applicant(s):     LOCKHEED CORP [US] +
Classification:    
- international:     B23K1/018; B23K31/02; C08K9/02
- european:    
Application number:     US201113103016 20110506
Priority number(s):     US201113103016 20110506 

LOW-SILVER-CONTENT SOLDER ALLOY AND SOLDER PASTE COMPOSITION

Espacenet This low-silver-content solder alloy comprises 0.05-2.0 mass% of silver, 1.0 mass% or less of copper, 3.0 mass% or less of antimony, 2.0 mass% or less of bismuth, 4.0 mass% or less of indium, 0.2 mass% or less of nickel, 0.1 mass% or less of germanium and 0.5 mass% or less of cobalt (wherein the content of each of the above-mentioned elements copper, antimony, bismuth, indium, nickel, germanium and cobalt is not 0 mass%), with the remainder being tin. According to the present invention, it becomes possible to provide a low-silver-content solder alloy which has a reduced Ag content and therefore can be produced at reduced cost, has excellent stretching properties, an excellent melting point, excellent strength and the like, and also has high fatigue resistance (cold thermal fatigue resistance) and long-lasting reliability.

WO2012056753  (A1)  -  LOW-SILVER-CONTENT SOLDER ALLOY AND SOLDER PASTE COMPOSITION
Inventor(s):     IMAMURA YOJI [JP]; IKEDA KAZUKI [JP]; PIAO JINYU [JP]; TAKEMOTO TADASHI [JP] +
Applicant(s):     HARIMA CHEMICALS INC [JP]; IMAMURA YOJI [JP]; IKEDA KAZUKI [JP]; PIAO JINYU [JP]; TAKEMOTO TADASHI [JP] +
Classification:    
- international:     B23K35/22; B23K35/26; C22C13/00; C22C13/02
- european:    
Application number:     WO2011JP60983 20110512
Priority number(s):     JP20100242916 20101029
Also published as:    
JP4787384  (B1)  

Effect of Ni on phase stability and thermal expansion of Cu 6-xNi xSn 5 (X = 0, 0.5, 1, 1.5 and 2)

Scopus: The crystallography of the Cu 6Sn 5 intermetallic that forms at the solder-substrate interface in many soldering operations can be influenced by Ni additions. It has been established that when Ni is present at 5-9 at%, the high-temperature hexagonal Cu 6Sn 5 (η) does not transition to the low-temperature monoclinic Cu 6Sn 5 (η') at the equilibrium temperature of 186 'C. In fact, the hexagonal phase remains stable from room temperature to 250 'C. This paper shows the stabilising effect of Ni exists in the range of 4.6-17.2 at% Ni in stoichiometric samples, over the larger temperature range of -100 to 250 'C using synchrotron X-ray diffraction. The results are also used in combination with dilatometry experiments and show that Ni decreases the magnitude of thermal expansion, and prevents the discontinuity in expansion that occurs with the polymorphic transformation

Intermetallics
Volume 26, 2012, Pages 78-85
Effect of Ni on phase stability and thermal expansion of Cu 6-xNi xSn 5 (X = 0, 0.5, 1, 1.5 and 2)  ( Articles not published yet, but available online Article in press About articles in press (opens in a new window) )

Nogita, K. , Mu, D., McDonald, S.D., Read, J., Wu, Y.Q. 

School of Mechanical and Mining Engineering, The University of Queensland, 43 Cooper Rd., St. Lucia, Brisbane, Queensland 4072, Australia

Electrorecrystallization of intermetallic compound in the Sn0.7Cu solder joint

Scopus: The electrorecrystallization, recrystallization driven by electrical current stressing, of Cu 6Sn 5 intermetallic compound occurs in a Sn0.7Cu flip chip solder bump. The Cu 6Sn 5 dissolves in Sn0.7Cu at 1.0 x 10 4 A/cm 2 of current stressing under 150'C. The Cu flux in the solder joint, driven by the combination force of thermal gradient and electromigration, flows toward the cold side of the solder joint. The segregation of Cu results in recrystallization and thus redistribution of IMC at the cold side of the solder joint after current stops

Intermetallics
Volume 26, 2012, Pages 40-43
Electrorecrystallization of intermetallic compound in the Sn0.7Cu solder joint  ( Articles not published yet, but available online Article in press About articles in press (opens in a new window) )

Chen, W.-Y.a , Chiu, T.-C.a, Lin, K.-L.a, Lai, Y.-S.b 

a  Department of Materials Science and Engineering, National Cheng Kung University, No.1, University Road, Tainan 70101, Taiwan
b  Central Labs, Advanced Semiconductor Engineering, Inc., Kaohsiung 81170, Taiwan

KICs 247 Wave Revolutionizes the Wave Process in Asia - 2012 EM Asia Innovation Award

Thomasneta: KIC announces that it has been awarded a 2012 EM Asia Innovation Award in the category of Software - Process Control Tools for its KIC 24/7 Wave. The award was presented to Ronnie Teo during an April 26, 2012 ceremony in Shanghai during NEPCON China.

The new KIC 24/7 Wave utilizes embedded sensors in the wave solder machine to automatically measure the thermal profile for each and every processed PCB to the acceptable process window. A thermocouple also is installed in the solder pot to constantly measure the pot temperature. In addition, the KIC 24/7 Wave reduces setup time by quickly suggesting the most optimum recipe for each and every PCB.

Any out of spec situation is immediately identified, while the standard SPC charts automatically provide Cpk numbers with the ability to provide alarms when the process starts drifting. Every PCB profile is recorded for easy retrieval for full process traceability. Traceability down to the individual PCB is achieved when bar codes are used.

The initial programming of the KIC 24/7 Wave is performed with a KIC profiler. The KIC profiler is capable of quickly identifying the appropriate wave solder settings for an improved process.

Established in 2006, the EM Asia Innovation Awards program strives to recognize and celebrate excellence in the Asian electronics industry, inspiring companies to achieve the highest standards and push the industry forward.

The influence of soldering conditions on conductivity, structure and strength of Cu/Sn96Ag4 solders

Scopus : In the paper the electrical properties of the Cu/Sn96Ag4 solders were studied. The studied solders were produced at 200, 220 and 250'C and within time range 3 to 90 s. Soldering temperatures were chosen to assure the best soldering conditions for the Cu/Sn96Ag4 alloy. The most appropriate temperature of 200'C is the one just above the melting point. The temperature of 250'C is the maximal one recommended by producers, which can be applied for the electronic elements during soldering. The studies have shown that the best electrical properties and tensile strength R m have samples soldered at times 3 and 30 s, while the highest specific resistance together with the lowest Rm value are observed for samples soldered at the time of 10 s.

The soldering temperature have small influence on the strength of the connection/bond however it shows significant affect on the electrical properties.

Archives of Metallurgy and Materials
Volume 57, Issue 1, 1 March 2012, Pages 33-37
The influence of soldering conditions on conductivity, structure and strength of Cu/Sn96Ag4 solders

Boczkal, G., Marecki, P., Perek-Nowak, M. 

Faculty of Non-Ferrous Metals, Department of Metallic Materials and Nano-Engineering, AGH-University of Science and Technology, 30 Mickiewicza Av., 30-059 Kraków, Poland

Orgalime seek to clarify RoHS2 scope questions

Orgalime document
New guidance document tries to resolve some very tricky issues but asks lots of complicated questions and overall just shows how complicated it is all going to be


Following Orgalime¡¦s recent participation in the RoHS2 FAQ Working Group meeting, our industry provides this outline of its common understanding of the scope provisions of Directive 2011/65/EU on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment (¡§RoHS2¡¨).

The background to this paper is twofold:
1. It substantiates the initial understanding expressed in Orgalime¡¦s RoHS2 Guide of July 2011 and aims at particularly clarifying the background to the position of the affected industry
„h that the compliance obligations with the substance restrictions and CE marking obligations established by RoHS2 arise for manufacturers and importers of EEE, however not for installers,
„h that the definition of ¡§electrical and electronic equipment¡¨ cannot be interpreted as targeting anything and everything with the slightest connection to electrical or electronic,
„h that any interpretative criteria in the context of RoHS2, and article 2.4 in particular, requires full respect of the legal text of the Directive and an ¡§ex ante¡¨ approach
in the light of the alignment of the RoHS Directive with the New Legislative Framework (NLF) and in view of preparing for RoHS2 compliance and for effective market surveillance and enforcement.

2. The draft FAQs are in our view built on a number of significant flaws, misunderstandings and erroneous starting points, including for example:
„h accepting that Member States have different interpretations of the existing RoHS Directive, despite the fact that it represents a fully harmonised product legislation and the existence of a Commission Guidance Document on the existing RoHS Directive, and accepting that they plan to perpetuate those differences in the implementation of RoHS2.
„h charging responsibilities and obligations on market operators regardless of the New Legislative Framework and of the official text of RoHS 2 itself, or
„h proposing unclear interpretations of the New Legislative Framework, which result in conflicting answers and misleading indications.

Orgalime also want the EU to revise the RoHS2 FAQ

Background

There are some related RoHS2 stories in the Soldertec newsfeed
Background EU webpage re RoHS2 FAQ etc
Previous ORGALIME RoHS2 Guidance document

Study on the progress of welding science and technology in China

Scopus : Welding is one of the most important technologies of materials forming and processing in modern manufacturing industry, the development of welding technology is of very important significance in promoting China to be a manufacturing giant in the world. Based on the summary and analysis of the recent advances on welding?science and technology?in China, the future?development strategies on the relative fields are proposed. Due to steels still hold the dominant role in the basic structural materials, the study of welding metallurgy for the new generation steels and the development of high grade welding consumables are the key topics in welding manufacturing.

China is now the largest electronic production site in the world, however, the study and development in lead-free soldering materials and lead-free packing technologies are the sole way to ensure China to be the largest green electronic producer. 

High energy density welding, such as laser beam welding and electron beam welding, is proven an advanced welding process which could increase the welding productivity remarkably, the study and application of such welding process in equipment manufacturing should be encouraged. The numerical simulation on welding process is beneficial in the understanding of the complex physical phenomena involved in welding, which also provides important and practical basic data. Significant progress in the simulation of thermal process, residual stress, deformation and welding metallurgy is made in China in the past years, nevertheless, the practical application of the above achievements should be further investigated. Achievements in research on automatic welding and intelligent welding have shown that the high productivity and welding quality could be reached by using welding automation, however, the integrated application of welding automation should be studied. The research and application on evaluation of integrity of welded structures should be emphasized in order to ensure fitness for purpose of such structures.


Jixie Gongcheng Xuebao/Journal of Mechanical Engineering
Volume 48, Issue 6, 20 March 2012, Pages 19-31
Study on the progress of welding science and technology in China

Li, X.a , Wu, C.b, Li, W.c 

a  College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124, China
b  College of Materials Science and Engineering, Shandong University, Jinan 250061, China
c  College of Materials Science and Engineering, Tianjin University, Tianjin 300072, China

SMTA China Announces 2012 Paper/Presentation Awards

EMSNow: SMTA China announced the Best and Excellent Paper and the Best and Excellent Presentation and Best Exhibit Awards at its annual awards presentation held in conjunction with SMTA China Annual Breakfast Reception and Recognition Ceremony, which took place on April 26, 2012 at the Shanghai Expo Intercontinental Hotel during NEPCON China in Shanghai.

 May Yan of Cisco Systems Ltd. was awarded the Best Paper of Technology Conference One (CE12) for the paper "Discussion on CU Dissolution in PB-Free PTH Rework".

Flextronics Industrial (Zhuhai) Co., Ltd.'s Carl Cai received the Excellent Paper of Technology Conference One (CE12) for the paper "Cycle Time Prediction and UPH Driving Methodologies Study for Fast Capacity Ramp Up".

Henley Zhou, Flextronics Industrial (Zhuhai) Co., Ltd., received The Best Paper of Technology Conference Two (CE12) for "A solution for BGA Underfill Partial Cured Issue and Coverage Issue".

IST-Integrated Service Technology Inc.'s Cherie Chen was awarded the Excellent Paper of Technology Conference Two (CE12) for the paper "The Surface Finish Effect on Creep Corrosion of PCB".

Jason Chan of Kyzen was awarded the Best Presentation of Technology Conference One (CE12) for the presentation "Cleaning Highly Dense Circuit Assemblies".

Cisco Systems Ltd.'s Xia Chuan received the Excellent Presentation of Technology Conference Two (CE12) for the presentation "Evaluation of an Alternative PB-Free Alloy Used in Wave Soldering Process".

Henley Zhou, Flextronics Industrial (Zhuhai) Co., Ltd., was awarded the Excellent Presentation of Technology Conference Two (CE12) for the presentation "A solution for BGA Underfill Partial Cured Issue and Coverage Issue".

Heraeus Zhaoyuan (Changshu) Electronic Materials Co., Ltd.'s Dai Peng received the Best Presentation of Vendor Conference One (CE12) for "Heraeus Products for High Reliability Application in Electronics".

Sunny Mu of Cookson Electronics-Enthone was awarded the Best Presentation of Vendor Conference Two (CE12) for the presentation "Considerations for the Long Term Reliability of PCBs in Harsh Environmental Conditions".

OK International's Paul Wood received the Best Presentation of Vendor Conference Three (CE12) for the presentation "Challenges of Rework on Micro BGAs".

The Best Emerging Exhibit of the Year 2012 China East award went to CyberOptics for its SE500 ULTRA solder paste inspection system.

The award for Best Exhibit Technology of the Year 2012 China East went to Assembléon Asia Ltd. for its iFlex high-precision flexible pick-and-place machine.

Electromigration in copper-core solder ball joints during thermal cycle tests

Scopus: Electromigration current densities in Cu and Al lines on a silicon die exceed 1.0�10 6 A/cm 2. However, solder joints can only withstand electromigration current densities below about 1.0�10 4 A/cm 2. Thus, electromigration in solder joints will become a problem in semiconductor packages in the near future. Previous studies demonstrated that Cu-core solder balls increased the electromigration lifetime and led to better current stability at temperatures below 423K. This is because electrons flow through the Cu cores, reducing the current density on the cathode side, which is where electromigration occurs. In the present study, we forcused on the reliability of solder joints in a combined environment by examining the effect of thermal cycle tests on the current in a new test sample. A new test sample for the evaluation of joining reliability by using Cu-core solder balls in a combined enbironment was made.

In initial tests, this test sample exhibited similar results to those observed in previous studies. Cu-core solder balls subjected to cyclic testing at 233/398K and a current density of 1.0×10 4 A/cm2 exhibited lower reliabilities than when there was no current.

Examination of cross-sections of the solder balls after reliability testing revealed that the combined environment accelerated growth of intermetallic compounds and cracks in the joining region. In a combined environment, Cu-core balls were converted into intermetallic compounds on the anode side. This phenomenon is thought to occur due to the different electrical resistivities of Cu-Sn intermetallic compounds.

ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, InterPACK 2011
Volume 2, 2011, Pages 719-723
ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, InterPACK 2011;Portland, OR;6 July 2011through8 July 2011;Code89456
Electromigration in copper-core solder ball joints during thermal cycle tests  ( Conference Paper )

Fujiwara, S.a, Chiwata, N.b, Fujiyoshi, M.c, Wakano, M.d, Tanie, H.e 

a  Hitachi, Ltd., Yokohama, Kanagawa, Japan
b  Hitachi Metals, Ltd., Minato-ku, Tokyo, Japan
c  Hitachi Metals, Ltd., Yasugi, Shimane, Japan
d  NEOMAX Kagoshima Co., Ltd., Izumi, Kagoshima, Japan
e  Hitachi, Ltd., Hitachinaka, Ibaraki, Japan

Effect of aging on tensile properties and microstructures of eutectic Sn-Pb solder with small amounts of Au and Pd for aerospace application

Scopus: In the joint with eutectic Sn-Pb solder and a lead-free Ni/Pd/Au electrode, degradation of mechanical properties of the solder due to dissolution of Au and Pd into the solder would be anxious.

In this study, the effect of aging was investigated on tensile properties and microstructures of the eutectic Sn-Pb solder with small amounts of Au and Pd added. In as-cast solders with both Au and Pd added, the tensile strength increases with increasing contents of Au and Pd. A similar tendency was observed after aging at 100'C for 1000 h. The effect of aging on elongation was relatively small and elongation degraded when brittle (Pd,Au) Sn 4 phases formed in the solder. In solders with Au ranging from 1 to 5 mass%, regardless of aging conditions investigated, the tensile strength is stable at approximately 50 MPa and 45 MPa before and after aging, respectively. The effect of aging on improvement of elongation was negligible and elongation degraded when rod shaped AuSn 4 formed in the solder.

On the basis of the result of microstructural observation, it was clarified that the strengthening by dispersion of (Pd,Au) Sn 4 phases is superior to softening by microstructure coarsening upon aging when the contents of Au and Pd are 2 mass% and 1 mass% or above, respectively

ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, InterPACK 2011
Volume 2, 2011, Pages 667-672
ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, InterPACK 2011;Portland, OR;6 July 2011through8 July 2011;Code89456
Effect of aging on tensile properties and microstructures of eutectic Sn-Pb solder with small amounts of Au and Pd for aerospace application  ( Conference Paper )

Kikuchi, R.a, Shohji, I.a, Saitoh, Y.a, Nemoto, N.b, Nakagawa, T.c, Ebihara, N.d, Iwase, F.e  


a  Gunma University, Kiryu, Gunma, Japan
b  Japan Aerospace Exploration Agency, Tsukuba, Ibaraki, Japan
c  Nippon Avionics Co., Ltd., Yokohama, Kanagawa, Japan
d  NEC TOSHIBA Space Systems, Ltd., Fuchu, Tokyo, Japan
e  HIREC Corp., Kawasaki, Kanagawa, Japan

Study of the thermomechanical inelastic energy response of backward compatible solder joints made with SN-3.8AG-0.7CU versus reballed SN37.0PB components

Scopus : Conflicting results in reliability tests for backward compatible and Pb-free soldered assemblies has motivated RoHS-exempted industries to practice reballing. Reballing is the name given to the process of removing Pb-free solder balls from the copper (Cu) pads of the Ball Grid Array (BGA) components received through the supply chain and replacing them with SnPb solder balls.

Recent studies on the subject of reballing have shown the possibility that the removed Pb-free solder ball leaves behind some intermetallic remnants of the Pb-free solder alloy and the Cu from the pads. A modeling approach based on physics of failure (PoF) is presented that quantifies the interactions between different thermal cycles applied to reballed Ball Grid Arrays (BGA) with remnants of the Pb-free solder alloy on the Cu pads. These resulting interactions are compared to backward compatible Sn-3.8Ag-0.7Cu (SAC) balls soldered with eutectic SnPb paste for the same thermal cycles. For the latter, the risk of having improper mixing during the assembly process is also studied. The approach is formulated at the microscale, incorporating physical mechanisms of the intermetallics created with Cu, and at the macroscale, capturing the creep phenomenon of the bulk solder as dominant failure driver.

Simulation results show that the reballed cases have higher inelastic energy density per cycle averaged over damage volume near the copper pads and that the inelastic energy density is higher across the bulk of the improperly mixed backward compatible solder balls when compared to properly mixed backward compatible solder balls.

The results of this study permit extrapolation of laboratory results to field life predictions and to explore the design of accelerated re-balled or backward compatible BGA tests that relate better to application-specific usage environments.

ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, InterPACK 2011
Volume 1, 2011, Pages 123-129
ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, InterPACK 2011;Portland, OR;6 July 2011through8 July 2011;Code89456
Study of the thermomechanical inelastic energy response of backward compatible solder joints made with SN-3.8AG-0.7CU versus reballed SN37.0PB components  ( Conference Paper )

Renta, L.M.a, Valentin, R.b, Quintero, P.b, Ma, D.c, Hovland, A.d 

a  University of Wisconsin - Madison, Madison, WI, United States
b  University of Puerto Rico - Mayagüez, Mayaguez, Puerto Rico
c  Lockheed Martin Co., Sunnyvale, CA, United States
d  Lockheed Martin Co., Denver, CO, United States

Crystal grain size and orientation important in solder fatigue for BGAs

Scopus: This paper presents the influence of the micro structure on the crack propagation in lead free solder joint. The author's group have studied the Manson-Coffin's law for lead free solder joint by using the isothermal fatigue test and FEM analytical approaches to establish the practicable evaluation of thermal fatigue life of solder joints, for example, for the Sn-Cu-Ni solder, because this solder is attracted from the aspect of the decrease of solder leach in the flow process and material cost. However, even if the same loading is given to the solder joints of BGA test piece, there was a large dispersion in the fatigue life.

Even though the effect of the shape difference has been considered, the range of the dispersion could not been explained sufficiently.

In the study, the fatigue crack propagation modes in the solder joints were investigated, and an internal fatigue crack mode and an interfacial fatigue crack mode were confirmed. And the tendency of a shorter on fatigue life in the interfacial fatigue mode was confirmed. To clarify the mechanism of these fatigue crack modes, the crystal grain size in the solder joints was investigated before the fatigue test and also after the test. Furthermore, the verification of the mechanism using FEM models considering the crystal grain size was carried out. First of all, each element in FEM models matching to the average crystal grain size was made. Second, the inelastic strain ranges in each FEM models were studied.

As a result, it was shown that the influence of the crude density of the crystal grain to the fatigue crack progress can be evaluated. In addition, the micro structure of the solder joint of large-scale electronic devices is observed, and FEM model was made based on the observation result. As a result, it was shown that the influence of the directionality with the crystal grain to the fatigue crack progress can be evaluated.

ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, InterPACK 2011
Volume 2, 2011, Pages 691-700
ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, InterPACK 2011;Portland, OR;6 July 2011through8 July 2011;Code89456
Effect of micro structure on fatigue characteristics of lead free solder joints  ( Conference Paper )

Akutsu, T., Yu, Q. 

Yokohama National University, Yokohama, Kanagawa, Japan

High strain rate fracture behavior of Sn-Ag-Cu solder joints on Cu substrates

Scopus: During service, micro-cracks form inside solder joints, making a microelectronic package prone to failure particularly during a drop. Hence, the understanding of the fracture behavior of solder joints under drop conditions, synonymously at high strain rates and in mixed mode, is critically important.

This study reports: (i) the effects of processing conditions (reflow parameters and aging) on the microstructure and fracture behavior of Sn-3.8%Ag-0.7%Cu (SAC387) solder joints attached to Cu substrates, and (ii) the effects of the loading conditions (strain rate and loading angle) on the fracture toughness of these joints, especially at high strain rates. A methodology for calculating critical energy release rate, G C, was employed to quantify the fracture toughness of the joints.

Two parameters, (i) effective thickness of the interfacial intermetallic compounds (IMC) layer, which is proportional to the product of the thickness and the roughness of the IMC layer, and (ii) yield strength of the solder, which depends on the solder microstructure and the loading rate, were identified as the dominant quantities affecting the fracture behavior of the solder joints.

The fracture toughness of the solder joint decreased with an increase in the effective thickness of the IMC layer and the yield strength of the solder. A 2-dimensional fracture mechanism map with the effective thickness of the IMC layer and the yield strength of the solder as two axes and the fracture toughness as well as the fraction of different fracture paths as contour-lines was prepared. Trends in the fracture toughness of the solder joints and their correlation with the fracture modes are explained using the fracture mechanism map.

ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, InterPACK 2011
Volume 2, 2011, Pages 763-771
ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, InterPACK 2011;Portland, OR;6 July 2011through8 July 2011;Code89456
High strain rate fracture behavior of Sn-Ag-Cu solder joints on Cu substrates  ( Conference Paper )

Huang, Z.a, Kumar, P.a, Dutta, I.a, Pang, J.H.L.b, Sidhu, R.c, Renavikar, M.c, Mahajan, R.c 

a  School of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164, United States
b  School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 639798, Singapore
c  Assembly Technology Development, INTEL Corporation, Assembly Technology Dev., AZ 85226, United States

Development of highly reliable BGA and flip-chip structures by using Cu-cored solder ball

Scopus: A Cu-cored solder joint is a micro-joint structure in which a Cu sphere is encased in solder. It results in a more accurate height and has low thermal and electrical resistance. In a previous paper, we examined the thermal fatigue life of a Cu-cored solder ball grid array (BGA) joint through actual measurements and crack propagation analysis. As a result, we found that the thermal fatigue life of a Cu-cored solder BGA joint is about twice as long as that of a conventional joint

In this paper, we describe the impact strength of a Cu-cored solder BGA joint determined by conducting an impact bending test. This test is a technique to measure the impact strength of a micro-solder joint. This method was developed by Yaguchi et al., and they confirmed that it is an easier and more accurate method of measuring impact strength than the board level drop test. First, we simulated the impact bending test by finite element analysis (FEA) and calculated solder strains of both Cu-cored solder joints and conventional joints. The results indicated that the maximum solder strain of a Cu-cored solder joint during the impact bending test was slightly smaller than that of a conventional joint. The solder volume of the Cu-cored solder joint was also smaller than that of a conventional joint. On the other hand, joint stiffness of the Cu-cored solder joint was larger than in a conventional joint. The former increases the solder strain of the Cu-cored solder joint, and the latter decreases it. By balancing these phenomena, it is possible to obtain a maximum solder strain in the Cu-cored solder joint that is slightly smaller than in a conventional joint. Based on these phenomena, the impact strength of the Cu-cored solder joint is predicted to be the same as or higher than that of a conventional joint. Therefore, we measured the impact strengths of a Cu-cored solder joint and a conventional joint using the impact bending test.

As a result, we confirmed that the impact strength of the Cu-cored solder joint was the same as or higher than that of a conventional joint. Accordingly, a Cu-cored solder BGA joint is a micro-joint structure that makes it possible to improve thermal fatigue life without decreasing impact strength. Moreover, we investigated whether the use of Cu-cored solder in a flip-chip (FC) joint improved its reliability. As a result, we found that the stress of an insulating layer on a Si die surface was reduced by using a Cu-cored solder FC joint. This is because bending deformation of the Cu land occurs, and the difference in thermal deformation between the Si chip and the Cu land becomes small. Accordingly, the Cu-cored solder FC joint is a suitable structure for improving reliability of a low-strength insulating layer.

ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, InterPACK 2011
Volume 2, 2011, Pages 725-732
ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, InterPACK 2011;Portland, OR;6 July 2011through8 July 2011;Code89456
Development of highly reliable BGA and flip-chip structures by using Cu-cored solder ball  ( Conference Paper )

Tanie, H.a , Chiwata, N.b, Wakano, M.c, Fujiyoshi, M.d, Fujiwara, S.e 

a  Hitachi, Ltd., 832-2, Horiguchi, Hitachinaka, Ibaraki, 312-0034, Japan
b  Hitachi Metals, Ltd., Tokyo, Japan
c  Neomax Kagoshima Co., Ltd., Kagoshima, Japan
d  Hitachi Metals, Ltd., Shimane, Japan
e  Hitachi, Ltd., Kanagawa, Japan

The effects of dopants on the aging behavior of lead free solders

Scopus  The microstructure, mechanical response, and failure behavior of lead free solder joints in electronic assemblies are constantly evolving when exposed to isothermal aging and/or thermal cycling environments. Over the past several years, we have demonstrated that the observed material behavior variations of Sn-Ag-Cu (SAC) lead free solders during room temperature aging (25 C) and elevated temperature aging (50, 75, 100, 125, and 150 C) were unexpectedly large and universally detrimental to reliability.

The measured stress-strain data demonstrated large reductions in stiffness, yield stress, ultimate strength, and strain to failure (up to 50%) during the first 6 months after reflow solidification. In addition, even more dramatic evolution was observed in the creep response of aged solders, where up to 100X increases were found in the steady state (secondary) creep strain rate (creep compliance) of lead free solders that were simply aged at room temperature. For elevated temperature aging at 125 C, the creep strain rate was observed to change even more dramatically (up to 10, 000X increase). There is much interest in the industry on establishing optimal SAC-based lead free solder alloys that minimize aging effects and thus enhance thermal cycling and elevated temperature reliability. During the past year, we have extended our previous studies to include several doped SAC alloys (SAC-X) where the standard SAC alloys have been modified with small percentages of one or two additional elements (X). Materials under consideration include SAC0307-X, Sn-.7Cu-X, SAC305-X, SAC3595-X and SAC3810-X. Using dopants (e.g. Bi, In, Ni, La, Mg, Mn, Ce, Co, Ti, etc.) has become widespread to enhance shock/drop reliability, and we have extended this approach to examine the ability of dopants reduce the effects of aging and extend thermal cycling reliability. In the current paper, we concentrate on showing results for SACX TM, which has the composition Sn-0.3Ag-0.7Cu-X with X = 0.1Bi. We have performed aging under 5 different conditions including room temperature (25 C), and four elevated temperatures (50, 75, 100 and 125). We have also extended the duration of aging considered in our experiments to up to 12 months of aging on selected alloys. Variations of the mechanical and creep properties (elastic modulus, yield stress, ultimate strength, creep compliance, etc.) have been observed. We have correlated the aging results for the doped SAX-X alloy with our prior data for the "standard" lead free alloys SACN05 (SAC105, SAC205, SAC305, SAC405).

The doped SAC-X alloy shows improvements (reductions) in the aging-induced degradation in stiffness, strength, and creep rate when compared to SAC105, even though it has lower silver content. In addition, the doped SAC-X alloy has been observed to reach a stabilized microstructure more rapidly when aged.

Mathematical models for the observed aging variations have been established so that the variation of the stress-strain and creep properties can be predicted as a function of aging time and aging temperature.

ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, InterPACK 2011
Volume 2, 2011, Pages 733-748
ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, InterPACK 2011;Portland, OR;6 July 2011through8 July 2011;Code89456
The effects of dopants on the aging behavior of lead free solders  ( Conference Paper )

Cai, Z., Suhling, J.C. , Lall, P., Bozack, M.J. 

Center for Advanced Vehicle Electronics, Auburn University, Auburn, AL 36849, United States

Quantifying the effect of porosity on the evolution of deformation and damage in Sn-based solder joints by X-ray microtomography and microstructure-based finite element modeling

Scopus: The presence of reflow porosity in Sn-based solder alloys is one of the key factors affecting their reliability and mechanical performance. In this study we have used X-ray microtomography to visualize the reflow porosity in a Pb-free solder joint and to reconstruct a three-dimensional model based on the exact geometry of the pores. Interrupted shear tests and subsequent tomography were conducted to image the joint at several stages of deformation. The initial reconstructed microstructure was used as a basis for a finite element (FE) model to simulate damage and predict failure of the single lap shear joint. Sphericity analysis was conducted to verify the accuracy of the FE results. The deformation predicted by the FE simulation incorporating the ductile damage model showed very good agreement with experimental observations. The model was also able to accurately predict the crack nucleation sites and propagation path.

Acta Materialia
Volume 60, Issue 9, 2012, Pages 4017-4026
Quantifying the effect of porosity on the evolution of deformation and damage in Sn-based solder joints by X-ray microtomography and microstructure-based finite element modeling  ( Articles not published yet, but available online Article in press About articles in press (opens in a new window) )

Padilla, E., Jakkali, V., Jiang, L., Chawla, N.  

Materials Science and Engineering, Arizona State University, Tempe, AZ 85287-6106, USA

Low Ag alloys reliability studies in Malaysia

Factiva: "The purpose of this paper is to discuss the reliability of board level Sn-Ag-Cu (SAC) solder joints in terms of both thermal cycling and drop impact loading conditions, and further modification of the characteristics of low Ag-content SAC solder joints using minor alloying elements to withstand both thermal cycle and drop impact loads. Design/methodology/approach - The thermal cycling and drop impact reliability of different Ag-content SAC bulk solder will be discussed from the viewpoints of mechanical and micro-structural properties," investigators in Kuala Lumpur, Malaysia report.

"The best SAC composition for drop performance is not necessarily the best composition for optimum thermal cycling reliability. The content level of silver in SAC solder alloys can be an advantage or a disadvantage depending on the application, package and reliability requirements. The low Ag-content SAC alloys with different minor alloying elements such as Mn, Ce, Bi, Ni and Ti display good performance in terms of both thermal cycling and drop impact loading conditions. Originality/value - The paper details the mechanical and micro-structural properties requirements to design a robust bulk SAC solder joint," wrote D.A.A. Shnawah and colleagues, University of Malaya.

The researchers concluded: "These properties provide design and manufacturing engineers with the necessary information when deciding on a solder alloy for their specific application."

Shnawah and colleagues published their study in Microelectronics International (A review on effect of minor alloying elements on thermal cycling and drop impact reliability of low-Ag Sn-Ag-Cu solder joints. Microelectronics International, 2012;29(1):47-57).

For additional information, contact D.A.A. Shnawah, Univ Malaya, Dept. of Elect Engn, Kuala Lumpur, Malaysia.

METHOD FOR FORMING TIN OR SOLDER COAT FILM AND DEVICE THEREFOR (WO2012060022A1)

WO2012060022A1A method for forming a tin or solder coat film on a small electrode pad or on a lead surface with a narrow pitch on an electronic circuit substrate or in an electronic component, the method including: a first step of placing tin or solder particles on a cleaned pad or a cleaned lead surface that is exposed on the electronic circuit substrate or an electronic component assembly (hereinafter referred to as "workpiece"), wherein the surface except the pad or the lead is covered by a solder resist film; a second step of fusing, as cores, the tin or solder particles on the pad or the lead surface to form the tin or solder coat film; and a third step of spraying high-temperature organic fatty acid solution on a surface of the tin or solder coat film to blow away the excessively attached tin or solder. Consequently, a uniform tin or solder coat film having the thickness of 2 to 20 um with the thickness variation being  3 um or less is formed on the pad or the lead

ISHIKAWA HISAO; Japan 〒32
YOKOYAMA MASANORI; Japan 〒32
Assignee:     HORIZON TECHNOLOGY LABORATORY CO., LTD. Japan〒32
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Published / Filed:     2012-05-10 / 2010-12-16
Application Number:     WO2010JP0073262

Reducing Formation Of Oxide On Solder (US20120111925A1)

US20120111925A1: In certain embodiments, a system includes a deposition system and a plasma/bonding system. The deposition system deposits a solder outwardly from a substrate of a number of substrates. The plasma/bonding system comprises a plasma system configured to plasma clean the substrate and a bonding system configured to bond the substrates. The plasma/bonding system at least reduces reoxidation of the solder.
In certain embodiments, a method comprises depositing solder outwardly from a substrate, removing metal oxide from the substrate, and depositing a capping layer outwardly from the substrate to at least reduce reoxidation of the solder.

Certain embodiments of the invention may provide one or more technical advantages. A technical advantage of one embodiment may be that a plasma/bonding system may be used to at least reduce (or even prevent) formation of metal oxide. The system may plasma clean and then bond wafers without exposing the wafers to oxygen, which may at least reduce formation of metal oxide. A technical advantage of one embodiment may be that a capping layer may protect a wafer from exposure to oxygen, which may reduce formation of metal oxide.

Inventor:     Diep, Buu; Murphy, TX, United States of America
Kocian, Thomas A.; Dallas, TX, United States of America
Gooch, Roland W.; Dallas, TX, United States of America

Assignee:     Raytheon Company, Waltham, MA, United States of America
other patents from RAYTHEON COMPANY (466005) (approx. 2,859)
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Published / Filed:     2012-05-10 / 2011-09-13

Lead-free solder foil for use in component packaging - stacked semiconductor wafers

US20120111924A1: According to an aspect of the invention, there is provided a lead-free solder including an alloy rolled into a shape of sheet. The alloy includes: tin; from 10 wt % to less than 25 wt % of silver; and from 3 wt % to 5 wt % of copper. And the alloy is free from lead.
The alloy may include 10 wt % to 20 wt % of silver. The alloy may have a shape of sheet with a thickness from 40 μm to 120 μm. The alloy may have a shape of a disk with the same diameter as a joined member, for example, a semiconductor wafer.
According to another aspect of the invention, the solder or materials thereof are not powdered, and thin sheet-shaped lead-free solder which is an alloy containing tin, silver, and copper as main components can be obtained.
The lead-free solder according to the present invention has an advantage in that, the solder and materials thereof are alloyed and rolled in a shape of a thin sheet without powdering the solder and materials thereof, so that costs are reduced.

MAKITA, Kazuyuki; Tokyo, Japan
ICHINOSE, Masaki; Tokyo, Japan
WATASHIMA, Taketo; Tokyo, Japan
SOUTOME, Masayuki; Tokyo, Japan
YAMASHITA, Mitsuo; Tokyo, Japan
ASAGI, Takeshi; Tokyo, Japan
HIRAI, Masatoshi; Tokyo, Japan
MURATA, Toru; Tokyo, Japan

Assignee:     FUJI ELECTRIC SYSTEMS CO., LTD., Tokyo, Japan
other patents from FUJI ELECTRIC SYSTEMS CO., LTD. (844106) (approx. 1)
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Published / Filed:     2012-05-10 / 2012-01-18

A study of microstructural development, hardness and micro-creep of Sn-3.5Ag-0.7Cu lead-free solder alloy prepared by rapid solidification

Scopus: The Sn-3.5Ag-0.7Cu lead-free solder alloy has been prepared by normal casting and melt-spinning techniques to investigate the microstructural development, hardness and micro-creep of this alloy due to rapid solidification.

The microstructure of the rapidly solidified ribbons and ingot samples has been investigated by SEM and X-ray diffraction (XRD) techniques. The results showed that the structure of the alloy prepared by normal casting is composed of Cu-Sn and Ag-Sn IMCs finely dispersed in Sn matrix, while these fine dispersions are not present in the rapidly solidified sample indicating that the rapid solidification rate is high enough to retain most of the Ag and Cu elements in nonequilibrium supersaturated solid solutions of β-Sn. Additionally, the mechanical properties of both slowly and rapidly cooled samples are examined by using Vickers microhardness tester at different loads in the range of them 0.098 to 4.9 N. The hardness value of the rapidly cooled sample was found to be 1.3 times higher than that of the slowly cooled sample due to refinement of the rapidly cooled sample as well as the nonequilibrium solid solutions of Ag and Cu in the β-Sn matrix. Besides, indentation creep behavior of both slowly and rapidly cooled samples is examined by using Vickers microhardness tester for three different values of the applied loads.

Synthesis of Au-Sn alloy nanoparticles for lead-free electronics with unique combination of low and high melting temperatures

Scopus : Au-Sn alloy nanoparticles (ANPs) with 16-67 wt% Sn were successfully synthesized in the size range of 2-10 nm using chemical reduction method. X-ray diffraction confirmed the formation of AuSn phase with hexagonal structure and was further validated by microscopy and spectroscopy techniques. Chemical reduction is a more scalable and economical technique relative to other synthesis methods for solder alloy particles; it can produce particles in nanoscale range and can be conducted at room temperature. A significant depression in the melting transition (starting from 187 'C) was observed for the Au-Sn ANPs relative to the bulk eutectic point (T m = 280 'C at 30% Au). Au-Sn nanoparticles offer a unique set of advantages as lead-free soldering material. In nanoparticle state, they can reflow at lower temperatures leading to less thermal stresses in adjacent electronic components during the manufacturing process. After the initial reflow and solder joint formation (bulk state), they can reclaim bulk Au-Sn properties including permanent high melting temperatures (up to 420 'C) which can potentially lead to superior thermal and mechanical performance suitable for high temperature electronic applications such as military and aerospace.

Prediction of damage and fatigue life of high-temperature flip chip assembly interconnections at operations

Scopus: The determination of the real value of damage/plastic work density in solder joints from computer numerical modelling and its usage in fatigue life prediction models based on accumulated energy density is critical to improving the accuracy of predicted life of solder joints.

Commercial ANSYS software based on three-dimensional finite element analysis (FEA) was employed to investigate damage of bonded materials of lead-free solder joints in a flip chip (FC48D6.3C457) mounted on a printed circuit board (PCB). The trend behaviour of accumulated damage and fatigue life per cycle over many accelerated thermal cycles (ATCs) are also studied. The solder bumps deformation is modelled using ANAND's visco-plasticity and the performances of all other materials in the assembly were captured with appropriate material models.

It was observed that the difference in stress magnitude and amplitude between inter-metallic compounds (IMCs) at the die side and solder bulk was highest and the presence of IMC in the joints increases bump damage which occurs in three stages during temperature cycle loading.

These results demonstrate that while IMC impacts solder joint reliability, the bond at interconnect between IMC at the die side and solder bulk is most vulnerable to fatigue crack initiation and propagation. A new methodology to find accurate solder joint damage is presented. The findings show that average damage from cycle of hysteresis loop stabilisation to cycle of onset of tertiary damage demonstrates potential of being adequate in determining magnitude of the solder joint damage.

However, considering that damage evolution is in three-phase, we propose the use of polynomial function to estimate plastic work damage in FC solder joints.

Microelectronics Reliability
2012
Prediction of damage and fatigue life of high-temperature flip chip assembly interconnections at operations  ( Articles not published yet, but available online Article in press About articles in press (opens in a new window) )

Amalu, E.H. , Ekere, N.N. 

Electronics Manufacturing Engineering Research Group, School of Engineering at Medway, University of Greenwich, Chatham Maritime, Kent ME4 4TB, UK

Corrosion Behavior of Sn-3.0Ag-0.5Cu Lead-Free Solder in Potassium Hydroxide Electrolyte

Scopus : The corrosion behavior of Sn-3.0Ag-0.5Cu (SAC305) solder alloy in 6 M potassium hydroxide electrolyte was investigated using polarization analysis. The results revealed that SAC305 is susceptible to corrosion because of the dissolution of the Sn phase. The corrosion potential (E corr) and corrosion current density (i corr) obtained from the sample was -1.108 V vs Hg/HgO and 1.795 � 10 -4 A cm -2, respectively. In addition, microstructural and elemental characterization revealed the presence of tin oxide, Cu, and/or Ag-containing corrosion product on the surface of the corroded sample. The morphology of the samples was also observed to contain several pits, cracks, and pore-like structures

Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
2012, Pages 1-6
Corrosion Behavior of Sn-3.0Ag-0.5Cu Lead-Free Solder in Potassium Hydroxide Electrolyte  ( Articles not published yet, but available online Article in press About articles in press (opens in a new window) )

Liew, M.C., Ahmad, I., Lee, L.M., Nazeri, M.F.M., Haliman, H., Mohamad, A.A.  

School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia

Effect of surface oxide on the melting behavior of lead-free solder nanowires and nanorods

Scopus: Lead-free nanosolders have shown promise in nanowire and nanoelectronics assembly. Among various important parameters, melting is the most fundamental property affecting the assembly process. Here we report that the melting behavior of tin and tin/silver nanowires and nanorods can be significantly affected by the surface oxide of nanosolders. By controlling the nanosolder reflow atmosphere using a flux, the surface oxide of the nanowires/nanorods can be effectively removed and complete nanosolder melting can be achieved. The complete melting of the nanosolders leads to the formation of nanoscale to microscale spherical solder balls, followed by Ostwald ripening phenomenon. The contact angle of the microscale solder balls formed on Si substrate was measured by direct electron microscopic imaging. These results provide new insights into micro- and nanoscale phase transition and liquid droplet coalescence from nanowires/nanorods to spheroids, and are relevant to nanoscale assembly and smaller ball grid array formation

Applied Surface Science
2012
Effect of surface oxide on the melting behavior of lead-free solder nanowires and nanorods  ( Articles not published yet, but available online Article in press About articles in press (opens in a new window) )

Gao, F.a, Rajathurai, K.a, Cui, Q.a, Zhou, G.b, NkengforAcha, I.a, Gu, Z.a  

a  Department of Chemical Engineering, University of Massachusetts Lowell, Lowell, MA 01854, USA
b  Department of Mechanical Engineering, Binghamton University, State University of New York (SUNY), Binghamton, NY 13902, USA

Characterization of interfacial IMCs in low-Ag Sn-Ag-xCu-Bi-Ni solder joints

Scopus: This research investigated the effects of Cu content on the interfacial IMCs in low-Ag Sn-0.7Ag-xCu-3.5Bi-0.05Ni (x = 0.3, 0.5, 0.7, and 1.5 wt%, respectively) solder joints by deep-etching method and SEM observation. Experimental results indicated that as Cu content increased in the solder, the grain size of the IMCs increased and the thickness of the IMCs decreased on Cu substrate. When the concentration of Cu in the solder was 0.3 wt%, the IMC on the soldering interface was (Cu, Ni) 6Sn 5. The concentration of Ni in (Cu, Ni) 6Sn 5 IMC was significantly suppressed by the increase of Cu content in the solder. As Cu content increased to 1.5 wt%, the concentration of Ni in the IMC decreased to 0 and the IMC transformed from (Cu, Ni) 6Sn 5 to Cu 6Sn 5. Due to the increase of Cu content, more and more (Cu, Ni) 6Sn 5 grains nucleated on Ni substrate, and the morphology of (Cu, Ni) 6Sn 5 transformed from polyhedrons to tiny prisms.

Journal of Materials Science: Materials in Electronics
2012, Pages 1-5
Characterization of interfacial IMCs in low-Ag Sn-Ag-xCu-Bi-Ni solder joints  ( Articles not published yet, but available online Article in press About articles in press (opens in a new window) )

Liu, Y., Sun, F. , Liu, Y. 

School of Material Science and Engineering, Harbin University of Science and Technology, 4# Linyuan Road, Harbin, 150040, China