SRC GeorgiaTech research to replace solder with copper in flip-chip

Semiconductor Research Corporation - SRC: "The second advancement is the actual connection between the chip and substrate. Both the chip and the substrate use copper wiring. The weak link between them is the solder, which is the only non-copper element in the pathway. Solders are mechanically brittle and limit both the density and performance of flip-chip connections between chips and boards. Georgia Tech researchers are replacing solder with all-copper connections, which are made into non-spherical structures, such as shielded, co-axial or other shapes that enable higher densities and performance than current solder materials.

Not only does this approach support continued system performance improvements, but also provides an environmental improvement by creating a smaller chemical footprint during fabrication."

Selective soft laser soldering

OptoIQ: "With regard to peel force and contact resistance, the quality of the laser soldered joints exceeds that of other contacting technologies. The peel force is higher by a factor of 3, whereas the thermal resistance is only about 14% of the contact solder joint.

DILAS, the diode laser company, is focused on delivering the most innovative technologies and advanced product solutions for the industrial market. Diode-based laser soldering is one example.

For further information, please contact Dave MacLellan, sales manager, Micro Division, Rofin-Baasel UK Limited, sales@rofin-baasel.co.uk."

Poll Results: On lead-free hand soldering

Poll Results:: "When asked 'Can you get on with lead-free hand soldering?', 24% responded Yes (but it looks worse than tin-lead), another 24% also responded Yes (but it is a struggle) and a completely happy 6% said Yes (and it looks great!). In total, 54% responded positively (however qualified the approval was)."

Conductive adhesives offer alternative to traditional solder connections for c-Si solar modules

EETimes: "The Hysol Eccobond CA3556HF from Henkel offers an alternative to traditional solder connections used for c-Si solar modules which can be problematic for emerging thin, fragile solar cells. The compound has been formulated to deliver low temperature curing at 150'C and an exceptionally fast cure time of five seconds.

The material provides an excellent bond between the Ag and SnPbAg coated tabs and the c-Si cells, delivering a stable and reliable electrical connection over the life of the module. Thin-film module manufacturers have also successfully incorporated this material into processes that dictate low-stress, fast curing interconnection of cells and ribbons."

Effect of Ag content on the microstructure of Sn-Ag-Cu based solder alloys

Soldering & Surface Mount Technology: "By using XRD analysis in addition to energy dispersive spectroscopy (EDS) it was found that the main intermetallics were Cu6Sn5 and Ag3Sn in a Sn matrix. Plate-like ?-Ag3Sn intermetallics were observed for all four alloys. Solder alloys SAC105, SAC205 and SAC305 showed a similar microstructure, while SAC405 displayed a fine microstructure with intermetallic phases dense within the Sn matrix.

Originality/value – Currently, low-silver content SAC alloys are being investigated due to their lower cost, however, the overall reliability of an alloy can be greatly affected by the microstructure and this should be taken into consideration when choosing an alloy. The size and number of Ag3Sn plate-like intermetallics can affect the reliability as they act as a site for crack propagation."

M. Reid, (CTVR, Stokes Institute, University of Limerick, Ireland), J. Punch, (CTVR, Stokes Institute, University of Limerick, Ireland), M. Collins, (CTVR, Stokes Institute, University of Limerick, Ireland), C. Ryan, (CTVR, Stokes Institute, University of Limerick, Ireland)

Citation: M. Reid, J. Punch, M. Collins, C. Ryan, (2008

Cu alloy, Bi powder low temperature lead-free solder

Factiva: "Provided is a metal filler comprising a mixture of first metal particles with second metal particles, wherein the first metal particles are Cu-alloy particles containing Cu as the major component, which is an element being present at the highest ratio by mass, together with In and Sn; the second metal particles are Bi-alloy particles containing 40-70% by mass of Bi together with 30-60% by mass of one or more metals selected from among Ag, Cu, In and Sn; and the content of the second metal particles is 40-300 parts by mass per 100 parts by mass of the first metal particles. Also provided are a lead-free solder containing the aforesaid metal filler, a bonded structure formed by using the aforesaid lead-free solder, and a substrate to which a part provided with the aforesaid bonded structure is mounted"


 Publication No. WO/2010/098357 was published on Sept. 02.


Title of the invention: "METAL FILLER, LOW-TEMPERATURE-BONDING LEAD-FREE SOLDER AND BONDED STRUCTURE."


Applicants: Asahi Kasei E-materials Corporation (JP).


Inventors: Tomonori Kiyama (JP) and Norihito Tanaka (JP)

Properties of SnAgCu/SnAgCuCe soldered joints for electronic packaging

Scopus: "For quad flat packages (QFP256), lead-free soldered joints reliability in service is a critical issue. In this paper, soldering experiments of quad flat package (QFP256) devices were carried out by means of infrared reflow soldering system with Sn-3.8Ag-0.7Cu and Sn-3.8Ag-0.7Cu-0.03Ce lead-free solders, respectively, and the mechanical properties of micro-joints of the QFP devices were tested and studied by STR micro-joints tester. The results indicate that the tensile strength of Sn-Ag-Cu-Ce soldered joints is better than that of Sn-Ag-Cu soldered joints. In particular, the addition of trace Ce to the Sn-Ag-Cu solder can refine the microstructures and decrease the thickness of the intermetallic compound layer of Sn-Ag-Cu solder alloys. In addition, the stress-strain response of Sn-Ag-Cu/Sn-Ag-Cu-Ce soldered joints in quad flat packaging was investigated using finite element method based on Garofalo-Arrhenius model. The simulated results indicate creep distribution of soldered joints is not uniform, the heel and toe of soldered joints, the area between soldered joints and leads are the creep concentrated sites. The creep strain of Sn-Ag-Cu-Ce soldered joints is lower than that of Sn-Ag-Cu soldered joints"

Zhang, L.a , Xue, S.-B.a , Gao, L.-L.a , Sheng, Z.a , Zeng, G.a , Chen, Y.b , Yu, S.-L.a c

a College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, 210016 Nanjing, China

b Harbin Welding Institute, 150080 Harbin, China

c 14th Research Institute, China Electronics Technology Group Corporation, 210013 Nanjing, China

Effects of nano-structured particles on microstructure and microhardness of Sn-Ag solder alloy

Scopus: "In this research, the typical nano-structured Polyhedral Oligomeric Silsesquioxane (POSS) particles were incorporated into the Sn-3.5Ag eutectic solder paste by mechanically mixing to form lead-free composite solder. The effects of nano-structured POSS additions on the microstructure and mechanical properties of as-fabricated composite solder alloys were systematically investigated. Experimental results indicated that the average size and spacing distance of Ag3Sn intermetallic compounds (IMCs) in composite solder matrix decreased as compared to the Sn-3.5Ag eutectic solder. The 3 wt% addition of nano-structured POSS particles could enhance the microhardness of composite solder by 18.4% compared with the Sn-3.5Ag eutectic solder matrix. The average grain size and spacing distance of Ag3Sn IMCs in Sn-Ag 3 wt% POSS composite solder matrix reduced from 0.35 to 0.23 μm and from 0.54 to 0.32 μm, respectively. The refined Ag3Sn IMCs, acting as a strengthening phase in the solder matrix, could enhance the microhardness of the composite solders"

Tai, F., Guo, F., Xia, Z.D., Lei, Y.P., Shi, Y.W.

College of Materials Science and Engineering, Beijing University of Technology, 100 Ping Le Yuan, Chaoyang District, Beijing 100124, China

The study of mechanical properties of Sn-Ag-Cu lead-free solders with different Ag contents and Ni doping under different strain rates and temperature

Scopus: "In this paper, the tensile tests were conducted at 25'C to investigate the effect of Ag content and Ni doping on the microstructures and mechanical properties of Sn-3.0Ag-0.5Cu, Sn-2.0Ag-0.5Cu, Sn-1.0Ag-0.5Cu, Sn-1.0Ag-0.5Cu-0.05Ni and Sn-1.0Ag-0.5Cu-0.02Ni solders. The effect of strain rate on mechanical properties was investigated for each solder using stain rates of 10-5 s-1, 10-4 s-1, 10-3 s-1, 10-2 s-1 and 10-1 s-1. In addition, the effect of temperature on mechanical properties was investigated for Sn-1.0Ag-0.5Cu-0.02Ni solder by conducting tests at -35 'C, 25 'C, 75 'C and 125 'C."

Test results show that the elastic modulus, yield stress and ultimate tensile strength increase with increasing strain rate and Ag content, but they decrease with increasing temperature. The elastic modulus, yield stress and ultimate tensile strength are lower and the elongation is larger for Sn-1.0Ag-0.5Cu-0.05Ni solder compared with Sn-1.0Ag-0.5Cu-0.02Ni solder. The strain rate and Ag content dependent mechanical property models have been developed for Sn-Ag-Cu solders for the first time. In addition, the temperature and rate-dependent mechanical property models have also been developed for Sn-1.0Ag-0.5Cu-0.02Ni solder. The microstructures of solders were also analyzed. The Ag content affects Ag3Sn intermetallic compound dispersion and Sn dendrite size. The microstructures of solder have fine Sn dendrites and more dispersed IMC particles for the high Ag content solder, which makes the solder exhibit high strength and yield stress

Che, F.X.a b , Zhu, W.H.b , Poh, E.S.W.b , Zhang, X.W.a , Zhang, X.R.b

a Institute of Microelectronics, ASTAR (Agency for Science, Technology and Research), 11 Science Park Road, Singapore Science Park II, Singapore 117685, Singapore

b United Test and Assembly Center Ltd., 5 Serangoon North Ave 5, Singapore 554916, Singapore

The influence of addition of Al nano-particles on the microstructure and shear strength of eutectic Sn-Ag-Cu solder on Au/Ni metallized Cu pads

Scopus : "In Sn-Ag-Cu solder joints and solder joints containing Al nano-particles, a scallop-shaped Sn-Ni-Cu intermetallic compound layer was clearly observed at the interfaces after long time aging and multiple reflows, and the intermetallic compound layer thickness was substantially increased with an increase in the number of reflow cycles as well as the aging time. However, after the addition of Al nano-particles, an additional Sn-Al-Ag intermetallic compound was found on the top surface of the Sn-Ni-Cu intermetallic compound layer. The Sn-Ag-Cu solder joints containing 3 wt% Al nano-particles consistently displayed a higher shear strength than that of the plain Sn-Ag-Cu solder joints as well as a lower Al nano-particle content as a function of reflow cycles and aging time due to a second phase dispersion strengthening mechanism by the formation of fine Sn-Ag-Al intermetallic compound particles as well as a controlled fine microstructure"

Gain, A.K.a , Fouzder, T.a , Chan, Y.C.a , Sharif, A.b , Wong, N.B.c , Yung, W.K.C.d

a Department of Electronic Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong

b Department of Materials and Metallurgical Engineering, Bangladesh University of Engineering and Technology, Dhaka 1000, Bangladesh

c Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong

d Department of Industrial and Systems Engineering, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong

A novel cyclic process involving zinc for separating silver from lead-free solder residue

Scopus: "In this study, a novel cyclic process to separate silver from the lead-free solder residues using a metal solvent has been developed. The process uses zinc as a metal solvent which selectively forms intermetallic compounds with silver, followed by the volatilization separation step to recover zinc which can be reused as the metal solvent. Based on the results obtained, up to 90% of the silver in a lead-free solder residue was calculated to be separated into the dross phase through the sixth silver separation stage using the proposed process"

Implementation and Characterization of a Medical Ultrasound Phased Array Probe With New Pb-Free Soldering Materials

Scopus: "This paper shows the use of conductive adhesives for the implementation of a medical phased array probe, where the soldering material is located among a platelet of the piezoelectric and fingers. A comparison between electroacoustic measures on the elements soldered with an ECA and with the traditional technology Sn-Pb will be also shown. Moreover, in the field of biomedical application, it is also fundamental to assure that the performances of the transducer are maintained in the time. To this aim, some laboratory tests for the evaluation of the reliability performances of the new Pb-free soldering material are proposed, and the preliminary results are presented in this paper."

Oxidation of liquid solders for die attachment

Scopus: "This study deals with thermal oxidation behaviour in the liquid state of a commonly-used die-attach solder, Pb-Sn, and its potential Pb-free alternatives (Bi-Ag and Zn-Sn) from viewpoints of thermodynamics and kinetics. The characteristics of the oxidation reaction layers were investigated using XPS, XRD and AES. The superior performance in oxidation prevention of the Zn based alloys can be ascribed to their stable oxidative product, ZnO, which exhibits low free energy of formation, as well as slow growth rate"

Song, J.-M., Cheng, Y.-M., Tsai, C.-H.

Department of Materials Science and Engineering, National Dong Hwa University, Hailien 974, Taiwan

Effect of adding Ce on interfacial reactions between Sn-Ag solder and Cu

Scopus: "We investigated the effect of adding cerium (Ce) to low Ag content Sn-1.0wt.%Ag solder on the interfacial reactions between the Sn-1.0Ag solder and Cu substrate. The formation and growth of interfacial intermetallic compounds (IMCs) between the Sn-1.0Ag-0.3Ce solder and Cu substrate were studied and the results were compared to those obtained for the Ce-free Sn-1.0Ag/Cu and most promising Sn-3.0Ag-0.5Cu/Cu systems. The addition of Ce to the Sn-Ag solder significantly reduced the growth of the interfacial Cu-Sn IMCs, retarded the interfacial reactions between the solder and the substrate, and prevented the IMC from spalling from the interface. The Sn-1.0Ag-0.3Ce solder alloy had a good interfacial stability with the Cu substrate during solid-state isothermal aging in the viewpoint of IMC growth"

Yoon, J.-W., Noh, B.-I., Choi, J.-H., Jung, S.-B.

School of Advanced Materials Science and Engineering, Sungkyunkwan University, 300 Cheoncheon-dong, Jangan-gu, Suwon, 440-746, South Korea

Robust, simplified and solder-free assembly processing of electronics products

Scopus: "This paper describes a new solder-free electronics assembly process tentatively being called The OCCAM Process, in honor of the 14th century English philosopher and logician whose words inspired the concepts found herein. Products built by this process are expected to be more reliable than previous solder-free strategies (for example, using conductive adhesive as a solder substitute) as well as traditionally manufactured soldered assemblies. The process is a reverse-order interconnection solution that employs mature, low-risk, familiar core processing technologies in a novel sequence. Components are interconnected by means of copper plating after they are assembled into their final positions in an encapsulated module, thus doing away with conventional printed circuit boards. Prototype assemblies using this new technology are currently being characterized."

Fjelstad, J.

Verdant Electronics Inc., Sunnyvale, CA, United States

Technical Paper - Society of Manufacturing Engineers

Volume TP07PUB191, 2007, 26p

The effect of ultrasound on the gold plating of silica nanoparticles for use in composite solders

Scopus: "In order to produce electronic devices that can survive harsh environments it is essential that the solder joints are very reliable and this has led to the development of composite solders. One approach to the manufacture of such solders is to disperse silica nanoparticles into it to improve their mechanical and fatigue characteristics. However, this is difficult to achieve using bare silica particles because they are not 'wettable' in the solder matrix and so cannot be dispersed efficiently. In an attempt to alleviate this issue it has been found that if the silica nanoparticles are first plated with gold then this problem of wetting can, to some extent, be overcome. However, the particles must be completely encapsulated with gold which, using the method previously described by workers at Kings College London, was found to be difficult to accomplish.

In this short communication the effect of ultrasound on the gold coverage is described. Different frequencies of ultrasound were used (20, 850 and 1176 kHz) and it was found that higher frequencies of ultrasound improved the coverage and dispersion of the gold nanoparticles over silica during the seeding step compared to simple mechanical agitation. This subsequently led to a more complete encapsulation of gold in the plating stag"

Cobley, A.J.a , Mason, T.J.a , Alarjah, M.a , Ashayer, R.b , Mannan, S.H.b

a The Sonochemistry Centre, Coventry University, Faculty of Health and Life Science, Priory Street, Coventry, CV1 5FB, United Kingdom

b Department of Mechanical Engineering, Kings College London, Strand, London, United Kingdom

The effect of ultrasound on the gold plating of silica nanoparticles for use in composite solders

Scopus: "In order to produce electronic devices that can survive harsh environments it is essential that the solder joints are very reliable and this has led to the development of composite solders. One approach to the manufacture of such solders is to disperse silica nanoparticles into it to improve their mechanical and fatigue characteristics. However, this is difficult to achieve using bare silica particles because they are not 'wettable' in the solder matrix and so cannot be dispersed efficiently. In an attempt to alleviate this issue it has been found that if the silica nanoparticles are first plated with gold then this problem of wetting can, to some extent, be overcome. However, the particles must be completely encapsulated with gold which, using the method previously described by workers at Kings College London, was found to be difficult to accomplish.

In this short communication the effect of ultrasound on the gold coverage is described. Different frequencies of ultrasound were used (20, 850 and 1176 kHz) and it was found that higher frequencies of ultrasound improved the coverage and dispersion of the gold nanoparticles over silica during the seeding step compared to simple mechanical agitation. This subsequently led to a more complete encapsulation of gold in the plating stag"

Cobley, A.J.a , Mason, T.J.a , Alarjah, M.a , Ashayer, R.b , Mannan, S.H.b

a The Sonochemistry Centre, Coventry University, Faculty of Health and Life Science, Priory Street, Coventry, CV1 5FB, United Kingdom

b Department of Mechanical Engineering, Kings College London, Strand, London, United Kingdom

Proposed TSCA IUR rule specifically calls out electronics industry

EMSNow: "Electronics manufacturers who send byproducts and waste for recycling are included among the targets of a proposed rule from the EPA published on August 13.

The rule expands the reporting requirements under the Toxic Substances Control Act (TSCA) Inventory Update Reporting (IUR) rule that requires manufacturers of chemical substances to report on the manufacturing, importation, processing, and use of those chemical substances. The EPA estimates it will cost each facility $48,700 and take 792 hours to comply with the proposed rule."

SMTA China and Hong Kong Chapter Announce 2010 Best Paper/Presentation and Best Exhibit Awards

EMSNow: "SMTA China announced the Best Paper/Presentation and Best Exhibit Awards at its annual awards presentation held in conjunction with the SMTA China 5th Anniversary Keynote Breakfast Reception, which took place September 1, 2010 at the Futian Shangri-la, Shenzhen Hotel."

Nihon Superior Releases Video Results for Evaluation of SN100C and SAC305

EMSNow: "Nihon Superior Co. Ltd., a supplier of advanced soldering materials to the global market, has released a video demonstrating the results of an evaluation comparing the wettability and spreadability of SN100C and SAC305 solder alloys on stranded wire.

The video demonstrates that although SAC305 has a lower melting point, the superiority of SN100C's wettability and spreadability after melting results in faster total wetting and spreading over SAC305.

In general, wettability is evaluated with zero-cross time using the wetting balance test (JIS Z 3198 or IPC J-STD-003). However, it is recommended to verify the performance of wetting and spreading of solder onto a base material after melting, such as in this evaluation. The total wetting time appears to be a more realistic indication of the true wetting and spreadability of a solder than just the zero-cross time as demonstrated in the video."

New Soldering Technology for Flex Circuits

EMS007: "Essemtec Switzerland introduces a new solution for soldering heat-sensitive, flexible materials such as Mylar--a selective IR oven. The principle: The specifically selected wavelength of the IR radiation is absorbed by the solder joint, but not by the foil.

Mylar films used for membrane keyboards have a limited resistance against high temperatures. Therefore, electronic components, such as LED, cannot be connected using standard SMT solders. Instead, conductive glue or low-temperature solders are used. A European keyboard manufacturer went one step further in protecting sensitive materials by inventing selective soldering with infrared radiation."

ZnSn high temperature solders from Kawasaki

Factiva: "According to recent research from Kawasaki, Japan, 'Pb-based solders are used as high-temperature solders in power semiconductor devices. Although the use of Pb is globally restricted, alternative materials cannot replace the Pb-based solder.'

'This study proposes that the Pb-based solder can be replaced by Zn-Sn alloys. Die shear tests revealed that some Zn-Sn solder joints between Cu substrates had a higher shear strength between 300 K and 543 K than those between Fe-42Ni substrates. The microstructure of the Zn-Sn solder joints between Cu substrates showed network microstructures consisting of a Zn phase and epsilon-CuZn5 phase and direct connection between the network microstructures and intermetallic compound layer"

ZnSn high temperature solders from Kawasaki

Factiva: "According to recent research from Kawasaki, Japan, 'Pb-based solders are used as high-temperature solders in power semiconductor devices. Although the use of Pb is globally restricted, alternative materials cannot replace the Pb-based solder.'

'This study proposes that the Pb-based solder can be replaced by Zn-Sn alloys. Die shear tests revealed that some Zn-Sn solder joints between Cu substrates had a higher shear strength between 300 K and 543 K than those between Fe-42Ni substrates. The microstructure of the Zn-Sn solder joints between Cu substrates showed network microstructures consisting of a Zn phase and epsilon-CuZn5 phase and direct connection between the network microstructures and intermetallic compound layer"

Electronics Reliability Summit Goes Virtual

Global SMT and Packaging: "Trafalgar Publications announces that in addition to the physical conference, it will offer delegates outside of Europe the opportunity to attend the Electronics Reliability summit in Tallinn, Estonia, 21-23 September as a Virtual Delegate. Using specialized software that combines webcasting and a video display of the presenter, delegates will be able to remotely attend each presentation and join in the debate, or ask questions after each session using the chat and/or a Twitter facility."

Nihon Superior Wins ICEP Outstanding Paper Award！

Nihon Superior Co., Ltd.: "Nihon Superior is pleased to annouce that research they have sponsored at the University of Queensland, Australia, has provided the basis for the paper that earned an ICEP Outstanding Paper Award.

The Award, presented during the opening ceremony of ICEP 2010 in Sapporo on May 12, was for the paper, “Inhibiting Cracking of Interfacial Cu6Sn5 by Ni Additions to Sn-based Lead-free Solders” that was presented by the lead author, The University of Queensland's Associate Professor Kazuhiro Nogita, at ICEP 2009 in Kyoto. The paper, which reports a phenomenon that explains a major contribution to the reliability of Nihon Superior’s SN100C solder alloy was co-authored by Stuart McDonald, Hideaki Tsukamoto and Jonathan Read of University of Queensland and the president of Nihon Superior, Tetsuro Nishimura and Shoichi Suenaga of Nihon Superior."

Canada proposes action against decaBDE and HBCD

Canada proposes action against decaBDE and HBCD: "Environment Canada has published a final revised risk management strategy for polybrominated diphenyl ethers (PBDEs) following the results of a final ecological state-of-the-science report on decabromodiphenyl ether (decaBDE), which concludes that decaBDE may accumulate to high and problematic levels in organisms, and may transform into bioaccumulative and potentially bioaccumulative substances. The brominated flame retardant industry association..."

Indium Features New Solder Paste in China

EMS00: "Indium8.9HF-1 Solder Paste is a no-clean, lead-free, halogen-free paste that offers the best-in-class probe-testability and unprecedented stencil print transfer efficiency to work in the broadest range of processes.

The paste was specially designed to be extremely thermally stable and maintain a soft, pliable residue after reflow. This means easier probe-testability and fewer false rejects during in-circuit testing.

Indium8.9HF-1 has a high oxidation barrier to eliminate graping and head-in-pillow defects and features excellent print transfer efficiency on 0.4 mm pitch CSPs and is halogen-free per the EN14582 test method.

The paste exhibits low voiding (<5%) over many different profiles when soldering BGAs with via-in-pad technology. It also offers a very robust processing window that can minimize potential defects, as well as accommodate various board sizes and throughput requirements. Indium8.9HF-1 is also compatible with Sn/Pb alloys.

The performance benefits customers obtain by using Indium8.9HF-1 result in increased cost savings and the highest finished goods reliability.

Indium will be exhibiting in booth #2F55 NEPCON Shenzhen."

Foxconn sees thirteenth suicide - is hiring mature employees to avoid more jumps

EMSNow: "A female employee of Foxconn Electronics' (Hon Hai Precision Industry's) Shenzhen plant fell to her death on August 4 despite the company having already taken many steps to try to prevent such tragedies from happening.

Foxconn pointed out that the company will assist the employee's family for funeral affairs and will cooperate with local police with their investigation."

Lead-Free in Mission Critical: Failure Is Not An Option

EMS007: "We had already begun addressing lead-free issues of the complex components that are increasingly multi-functional, miniaturized, and subject to reflow during their build. Efforts included adjusted profiling guidelines, component shielding during reflow, more advanced test and inspection (over, under, around and through), and if necessary, hand soldering.

But, because RoHS was only enacted in 2006, we still don't know whether those efforts alone will prove adequate for long-term mission-critical applications. The military, for instance, has said it wants a minimum of 15 years before first-repair. medical wants at least seven (usually more); and even automotive wants components to last seven to 10 years [1].

Lead-free problems exist, some of which we noted. Many will be solved only with increased R&D and empirical evidence. Many boil down to better OEM and EMS communication, particularly when assembling mission-critical components and boards offshore, where differences in language, experience and culture exist.|

There is, however, no agreed-upon scientific evidence that the environment will be helped more by full lead-free implementation than mission-critical industries will be hurt by it. While technology should always show concern for the environment, until environmental-friendly technology is proven to go the distance needed for mission-critical applications, we have much work to do. Failure is simply not an option.

In 2009, David Cavanaugh, Director, Corporate Component Engineering at Benchmark Electronics, said it will take four to five more years before we are able to have the confidence in lead-free that we do in tin/lead [2].�If he is correct, that would mean a minimum of at least three more years to go"

Reduction of lead free solder aging effects using doped SAC alloys

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. In our prior work on aging effects, we have demonstrated that large degradations occur in the material properties (stiffness and strength) and creep behavior of Sn-Ag-Cu (SAC) lead free solders during aging.

These effects are universally detrimental to reliability and are exacerbated as the aging temperature and aging time increases. Conversely, changes due to aging have been shown to be relatively small in conventional Sn-Pb solders. Aging effects for lead free solder materials are especially important for the harsh applications environments present in high performance computing and in automotive, aerospace, and defense applications"

CAVE, Auburn University, US

Effects of fine size lead-free solder ball on the interfacial reactions and joint reliability

Scopus: "As the trend of smaller mobile electronic products, smaller solder balls are needed for electronic packages such as chip scale package (CSP). The purpose of this study was to investigate the effect of solder ball sizes on the interfacial reaction and their joint reliability. In this study, 400, 300, and, 200 μm diameter solder balls of 98.5 wt.% Sn, 1 wt.% Ag, and 0.5 wt.% Cu(SAC105) were reflowed on the Cu/OSP and electroplated Ni/Au pads at 250C. In the case of the reaction with Cu/OSP, as solder ball sizes decreased, the thickness of Cu6Sn5 intermetallic compounds (IMCs) increased and Cu concentrations of bulk solder balls increased."

The Cu dissolution rate of finer solder balls into molten solder was faster than larger solder balls due to its high pad area/solder volume ratio (A/V ratio). Fast Cu dissolution into molten solder promoted the thicker IMC growth. In the case of the reaction with electroplated Ni/Au, (Cu,Ni)6Sn5 IMCs were only formed at the interface of 400 μm solder ball. Both (Cu,Ni) 6Sn5 and (Ni,Cu)3Sn4 IMCs were formed at the interface of 300 μm solder ball. The absolute amount of Cu in 200 μm solder ball was smaller than 300 and 400 μm solder ball due to its smaller volume, therefore (Ni,Cu)3Sn4 IMCs were formed by the insufficient amount of Cu at the interface of 200 μm solder ball. The substrate design with smaller A/V ratio and the SAC alloy with higher Cu contents (>0.5 wt.%) were recommended to reduce the IMC growth

A package demonstration with solder free compliant flexible interconnects

Scopus: "lexible, stress-engineered spring interconnects are a novel technology potentially enabling room temperature assembly approaches to building highly integrated and multi-chip modules (MCMs). Such interconnects are an essential solderfree technology facilitating the MCM package diagnostics and rework.

Previously, we demonstrated the performance, functionality, and reliability of compliant micro-spring interconnects under temperature cycling, humidity bias and high-current soak. Currently, we demonstrate for the first time the package with the 1st level conventional fine pitch C4 solder bump interconnects replaced by the arrays of microsprings. Dedicated CMOS integrated circuits (ICs) have been assembled onto substrates using these integrated microsprings. Metrology modules on the ICs are designed and used to characterize the connectivity and resistance of each microspring site.

Mn and Ce doping of SAC alloys 0 interview

Real Time With EMS007 Guest Editor Jasbir Bath grills Indium Corporation Vice President of Technology Dr. Ning-Cheng Lee on what effects Mn or Ce doping has on the reliability of SAC lead-free solder joints. Find out what the latest cost and reliability results are when adding these doping agents to SAC alloy.

Solidification cracking in low silver alloys

Factiva: "In the present work, the effect of Ag content on solidification cracking susceptibility of Sn-Ag-Cu solder joints has been investigated. Solders containing 1.0 wt.% to 3.8 wt.% Ag were used in the experiment,' scientists writing in the Journal of Electronic Materials report.

'Solidification cracks were created using a copper self-restraint specimen, which could simulate the process of solidification cracking. Meanwhile, solidification cracking susceptibility was evaluated by comparing the total crack length of the solder joint. The results indicate that solidification cracks exist in solder joints with 1.0 wt.% to 3.0 wt.% Ag content, whereas there are no cracks in Sn-3.8Ag-0.7Cu solder joints. When the Ag content increases from 1.0 wt.% to 3.0 wt.%, the total crack length of Sn-Ag-Cu solder joints increases to a maximum and then drops to zero when the Ag content reaches 3.8 wt.%,' wrote W. Lu and colleagues, Beijing University of Technology."

SnZn solderable coatings are whisker resistant etc

Factiva: "The present invention provides a surface treated steel sheet for electronic components simultaneously satisfying the solder wettability, whisker-proof property, and stability of appearance with aging while not containing hazardous substances with environmental impact such as lead and chromium and a method of production of the same, that is, a surface treated steel sheet for electronic components comprising steel sheet or Ni plated steel sheet plated with Sn and Zn and then treated by thermal diffusion or plated with Sn-Zn alloy to form an Sn-Zn alloy layer, wherein said Sn-Zn alloy layer is deposited in an amount of 3 g/m2 or more, the Sn-Zn alloy layer has a Zn (weight)/Sn (weight) ratio of 0.001 to 0.1, preferably 0.001 to 0.01, and this Sn-Zn alloy layer has an inorganic coating mainly comprised of phosphoric acid-zinc-magnesium in a P Zn Mg deposited amount of 0.1 to 100 mg/m2, preferably 0.1 to 10 mg/m2."

Nihon's SN100C Wets and Spreads Faster than SAC305

EMS007: "An evaluation of solder wettability and spreadability was conducted with lead-free flux cored solder wire of SN100C and SAC305 alloys on stranded wire used for speakers. SAC305 has a lower melting point; however, SN100C's superior wettability and spreadability after melting was proven over SAC305.

Generally, wettability is evaluated with zero-cross time using the wetting balance test (JIS Z 3198 or IPC J-STD-003). However, it is recommended that the performance of wetting and spreading of solder onto a base material be verified after melting, such as in this evaluation. The total wetting time appears to be a more realistic indication of true wetting and spreadability of a solder."

Delphi to Examine the Impact of Tin Whiskers

EMS007: "He will be describing Delphi's experiences with tin whiskers at the IPC conference at Electronics Midwest in Rosemont, Illinois, September 28-30, 2010. Platt will be one of five speakers in a session entitled 'Product Sustainability: Managing Tin Whiskers and Product Lifecycle Analysis.'

Delphi has plenty of knowledge about that product lifecycle. 'We've had lead-free components on lead-containing assemblies in the field since 1995; we've put a lot of lead-free componentry out there. We've tracked their performance and seen the impact tin whiskers can have in the field,' Platt said.

Despite all the fear surrounding tin whiskers on electronic components, they don't appear to be quite the prolific reliability challenge feared by many. 'Overall, we found limited damage from tin whiskers. Our position is that the risk associated solely with conversion to tin components is minimal,' Platt said. He added that electronic component suppliers have done a good job following mitigation strategies."

Nihon Superior Wins ICEP Outstanding Paper Award

PRLog: "The authors successfully developed a method of limiting cracking in the Cu6Sn5 intermetallic compounds, which are formed at the interface between lead-free solders and their Cu substrates. In this paper, it is shown that the level of cracking in the (Cu,Ni)6Sn5 reaction layer and the morphology of the intermatallics varies with the Ni content. To explore the mechanisms associated with the differences in joint integrity, detailed synchrotron X-ray powder diffraction (XRD) has been used with Rietveld analysis. The results show Ni stabilizes a high-temperature allotrope of the Cu6Sn5 phase, avoiding stresses induced by a volumetric change that would otherwise occur on phase transformation."

False Tin Whiskers: Masquerading Tin Copper Intermetallics

EMS007: "The SEM analysis results revealed the true identity of the whisker-like anomalies observed on the printed wiring assembly. The SEM EDS results show the copper/tin element ratio of the anomalies to be approximately six parts copper to five parts tin which would correspond to the Cu6Sn5 tin/copper intermetallic (IMC) phase [8]. The Cu6Sn5 tin/copper IMC phase forms in a needle morphology as the copper content of the solder begins to exceed approximately 0.3% [9, 10].

The Cu6Sn5 intermetallic needles often form and grow preferentially from component lead and/or printed wiring pad edges. The SEM analysis shows the same behavior for the whisker-like anomalies on the QFP component. The formation and observation of Cu6Sn5 intermetallic needles solder joint microstructure is a typical occurrence."

Zn addition retards tin whisker growth in SACCe

Factiva: "According to a study from Taipei, Taiwan, 'It has been reported that the rapid growth of tin whiskers occurring on the surface of rare earth containing solders can be prevented by the addition of 0.5 wt.% Zn into a Sn-3Ag-0.5Cu-0.5Ce alloy. The present study shows that the tensile strength of Sn-3Ag-0.5Cu-0.5Ce alloy alloyed with Zn increases significantly in comparison to the Zn-free Sn-3Ag-0.5Cu and Sn-3Ag-0.5Cu-0.5Ce solder.'

'Moreover, the growth of intermetallic compounds at the solder/pad interfaces during the thermal aging at 100 degrees C and 150 degrees C was inhibited by the Zn addition. Nevertheless, the excess of Zn addition to 0.5 wt.% causes poor junction in the Sn-3Ag-0.5Cu-0.5Ce packages,' wrote H.J. Lin and colleagues, National Taiwan University.

The researchers concluded: 'An optimized addition amount of Zn in Sn-3Ag-0.5Cu-0.5Ce solders is 0.2 wt.% for both inhibiting the growth of tin whiskers and strengthening the solder joints, although its ductility is still lower than that of the original Sn-3Ag-0.5Cu.'

Lin and colleagues published the results of their research in the Journal of Alloys and Compounds (Effects of Ce and Zn additions on the microstructure and mechanical properties of Sn-3Ag-0.5Cu solder joints. Journal of Alloys and Compounds, 2010;500(2):167-174)."

Leprosy of tin

The Dayside: "I first heard about tin pest (lpre d'etain, 'leprosy of tin,' in French) yesterday in the midst of reading a history of Singapore.

By the late 19th century, Singapore's prosperity had risen dramatically, thanks in part to the opening of the Suez Canal, the extension of the telegraph from Europe, and the development of Malaya's tin industry. Wondering why tin became a hot commodity, I turned to Wikipedia, where I encountered tin pest.

Tin is a soft, shiny metal that resists tarnishing and is nontoxic, which is why it has been used for more than a century to line steel food containers. The Wikipedia entry also told me about tin's principal allotropes (structural forms). The useful metal, known as white or β tin, is the stable allotrope above 13.2 'C. Below that transition temperature, a brittle, fragile insulator called gray or α tin is the more stable."

Immersion Tin eliminates tin whisker formation.

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The Inhibition of Tin Whiskers on the Surface of Sn-8Zn-3Bi-0.5Ce Solders

Scopus: "Through the refinement of the (Ce, Zn)Sn3 intermetallic phase, the formation of tin whiskers, previously observed on the surface of a Sn-3Ag-0.5Cu-0.5Ce solder, was prevented in a Sn-9Zn-0.5Ce alloy.

However, whisker growth can still occur on the surface of Sn-8Zn-3Bi-0.5Ce solder after air storage at room temperature and at 150'C due to the formation of large (Ce, Zn)Sn3 intermetallic clusters.

Further experiments showed that decreasing the Bi-content in this Sn-8Zn-0.5Ce alloy to 1 and 2 wt.% can recover the beneficial effects of Zn additions on the refinement of the (Ce, Zn)Sn3 phase and obviously reduce the appearance of tin whiskers.

In addition, alloying the Sn-8Zn-3Bi-0.5Ce solder with 0.5 wt.% Ge, which increases the oxidation resistance of the (Ce, Zn)Sn3 intermetallic clusters, can also effectively inhibit tin whisker growth"

Jain, C.C.a , Chen, C.L.a , Lai, H.J.b , Chuang, T.H.a

a Department of Materials Science and Engineering, National Taiwan University, Taipei 106, Taiwan

b Materials Research Laboratories, Industrial Technology Research Institute, Hsinchu, 31015, Taiwan

IEEE Special issue on tin whiskers

Scopus - Document details: "IEEE Transactions on Electronics Packaging Manufacturing
9 August 2010
Article in press
ISSN: 1521334X
CODEN: ITEPF
DOI: 10.1109/TEPM.2010.2063670
Document Type: Article in Press
Source Type: Journal


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Introduction to the Special Issue on Tin Whiskers

Osterman, M."