Effects of Co additions on electromigration behaviors in Sn-3.0 Ag-0.5 Cu-based solder joint

Scopus: "As the miniaturization trend of electronic packing industry, electromigration (EM) has become a critical issue for fine pitch packaging. The EM effects on microstructure evolution of intermetallic compound layer (IMC) in Sn-3.0 Ag-0.5 Cu XCo (X = 0, 0.05, 0.2 wt%) solder joint was investigated.

Findings of this study indicated that current stressing of Sn-3.0 Ag-0.5 Cu-0.2 Co solder joint with 104 A/cm2 at 50 'C for 16 days, no remarkable EM damages exhibited in solder matrix. Whereas, after current stressing at 150 'C for 1 and 3 days, Sn-3.0 Ag-0.5 Cu specimens showed obvious polarity effect between cathode and anode. Different morphology changes were also observed at both sides.

After current stressing for 1 day, two IMC layers, Cu6Sn5 and Cu3Sn, with wave type morphology formed at cathode. Sn phases were also observed inside in the IMC layer. However, only Cu6Sn5 formed in anode. Three days later, Sn phases were found in anode. Besides, Co additions, aging treatment, Ag3Sn, and other IMCs improved the resistance of EM by the evidence of retarding polarity effect"

Dowa make solder powder in solvent melt

Factiva: "A process for producing a solder powder is provided by which it is possible to efficiently obtain a solder powder having an average particle diameter of 0.05 m or larger but less than 3 m in a stable yield. The process for producing a solder powder comprises: a step in which a solid or liquid metal, a nonaqueous solvent, and balls for pulverization that have a diameter of 0.05-5 mm are introduced into a vessel to obtain a mixture; a step in which the mixture is heated to a temperature between (melting point of the metal)-5degC and (melting point of the metal) 20degC and stirred; a step in which the balls for pulverization are separated from the stirred mixture to obtain a mixture of a solder powder and the nonaqueous solvent; and a step in which the mixture of a solder powder and the nonaqueous solvent is subjected to solid-liquid separation to obtain the solder powder"

SAC TiO2 nanocomposites

Factiva: "Sn-Ag-Cu composite solders reinforced with nano-sized, nonreacting, noncoarsening 1 wt% TiO2 particles were prepared by mechanically dispersing TiO2 nano-particles into Sn-Ag-Cu solder powder and the interfacial morphology of the solder and flexible BGA substrates were characterized metallographically. At their interfaces, different types of scallop-shaped intermetallic compound layers such as Cu6Sn5 for a Ag metallized Cu pad and Sn-Cu-Ni for a Au/Ni and Ni metallized Cu pad, were found in plain Sn-Ag-Cu solder joints and solder joints containing 1 wt% TiO2 nano-particles"

In addition, the intermetallic compound layer thicknesses increased substantially with the number of reflow cycles. In the solder ball region, Ag3Sn, Cu6Sn5 and AuSn4 IMC particles were found to be uniformly distributed in the beta-Sn matrix. However, after the addition of TiO2 nano-particles, Ag3Sn, AuSn4 and Cu6Sn5 IMC particles appeared with a fine microstructure and retarded the growth rate of IMC layers at their interfaces,"

The researchers concluded: "The Sn-Ag-Cu solder joints containing 1 wt% TiO2 nano-particles consistently displayed a higher hardness than that of the plain Sn-Ag-Cu solder joints as a function of the number of reflow cycles due to the well-controlled fine microstructure and homogeneous distribution of TiO2 nano-particles which gave a second phase dispersion strengthening mechanism

wrote A.K. Gain and colleagues, City University of Hong Kong.

Polymer Matrices for Polymer Solder Hybrid Materials

Factiva: "Embodiments of the present invention provide various polymeric matrices that may be used as a binder matrix for polymer solder hybrid thermal interface materials. In alternative embodiments the binder matrix material may be phophozene, perfluoro ether, polyether, or urethane. For one embodiment, the binder matrix is selected to provide improved adhesion to a variety of interfaces. For an alternative embodiment the binder matrix is selected to provide low contact resistance. In alternative embodiments, polymeric materials containing fusible and non-fusible particles may be used in application where heat removal is desired and is not restricted to thermal interface materials for microelectronic devices."

SGS, ENVIRON Launch Exclusive Webinar on RoHS2

EMS007 : "The webinar – entitled “RoHS2 challenges and solutions” – will be held on Tuesday, June 28, 2011 from 4.00 to 5.00 pm Central European Time (10.00 to 11.00 am Eastern Time). It will explain the impact of the new RoHS2 scope, which applies to all products that are dependent on electrical power to fulfil at least one intended function. It will highlight the new legal obligations for distributors that apply immediately as soon as the new Member State RoH2 Regulations take effect – there is no phase-in period to take account of existing stocks of a distributor."

Copper pillar to be mainstream FC packaging technology in 2012

Digitimes: "IC packagers Advanced Semiconductor Engineering (ASE), Amkor Technology, Siliconware Precision Industries (SPIL) and STATS ChipPAC have all started developing a new flip-chip (FC) packaging technology dubbed copper pillar bumping, according to industry sources. The new packaging method will replace conventional solder bumping as the mainstream technology in 2012.

The transition to a new FC packaging technology is being sped up by growing demand for smaller form factors and low cost products such as smartphones, the sources indicated. Meanwhile, further advances in shrinking process geometries are also required to produce chips with high level of integration and low power consumption. While migrating to smaller-geometry processes, reducing manufacturing costs has become more fundamental for chip companies, the sources pointed out."

Taiwan SnBiCe whiskers?

Factiva: "According to a study from Taipei, Taiwan, 'The effects of a rare-earth element on the microstructure, mechanical properties, and whisker growth of Sn-58Bi alloys and solder joints in ball grid array (BGA) packages with Ag/Cu pads have been investigated. Mechanical testing indicated that the elongation of Sn-58Bi alloys doped with Ce increased significantly, and the tensile strength decreased slightly, in comparison with undoped Sn-58Bi.'

'In addition, the growth of both fiber- and hillock-shaped tin whiskers on the surface of Sn-58Bi-0.5Ce was retarded in the case of Sn-3Ag-0.5Cu-0.5Ce alloys. The growth of interfacial intermetallic compounds (IMC) in Sn-58Bi-0.5Ce solder joints was slower than that in Sn-58Bi because the activity of Ce atoms at the interface of the Cu6Sn5 IMC/solder was reduced. The reflowed Sn-58Bi and Sn-58Bi-0.5Ce BGA packages with Ag/Cu pads had a ball shear strength of 7.91 N and 7.64 N, which decreased to about 7.13 N and 6.87 N after aging at 100 degrees C for 1000 h, respectively,' wrote T.H. Chuang and colleagues, National Taiwan University.

The researchers concluded: 'The reflowed and aged solder joints fractured across the solder balls with ductile characteristics after ball shear tests."

T.H. Chuang, National Taiwan University, Institute Materials Science & Engineering, Taipei 106, TAIWAN.

Effect of Ag content on soldering ability of Sn-Ag-Cu solders

Scopus: "The influences of Ag content on melting temperature and wettability of Sn-xAg-0.5Cu (x=0.3, 0.5, 0.7, 0.9) lead-free solder alloys were studied. The melting temperatures of alloys were compared by DSC (differential scanning calorimetry) curves and the wettability was compared by the area and rate of wetting on Cu substrate.

The experimental results indicate that alloys with higher Ag content have lower melting points and melting range, and the content of Ag in solder alloys has a significant impact on the distribution and profile of the DSC curves. However, with the Ag content increasing, the wettability of the alloys degrades. By combining the two key properties of solder alloy, melting temperature and wettability, Sn-0.7Ag-0.5Cu shows higher performance"

Liu, Y., Sun, F., Liu, Y., Wang, J.

College of Material Science and Engineering, Harbin University of Science and Technology, Harbin 150040, China

Volume effect on shear strength of SnAgCu lead-free solder joints

Scopus: "Sn3.0Ag0.5Cu lead-free solder joints of different sizes in the range of 200 μm to 600 μm were multi-reflowed and aged, and then the shear strength of those solder joints were tested by the micro-force tester DAGE4000. The effect of solder volume differences on the shear strength of solder joints was investigated. The results indicated that the shear strength of SnAgCu lead-free solder joints decreased with the increasing of the solder joint volume, showing an apparent volume effect. The effect of aging time and reflow times on the shear strength of solder joints with different sizes were also discussed, and scanning electron microscopy (SEM) was used to analyze the morphology of shear fracture, and the failure mechanism of solder joints were discussed."

Wang, C., Wang, X., Tian, Y.

State Key Laboratory of Advanced Welding Production Technology, Harbin Institute of Technology, Harbin 150001, China

Improving the solderability and electromigration behavior of Low-Ag SnAgCu soldering

Scopus: "Compared with widely used SAC305 (Sn-3.0Ag-0.5Cu) solder, low-Ag (Ag≤1%) SAC solder obviously shows advantages in cost and mechanical impact resistance, and disadvantages in worse wettability, higher melting point and degeneration in electromigration, which restrict its application. Therefore, adding some suitable elements to the solder to improve the solderability and mechanical performance is very important for applications. In this paper, the solderability and electromigration behavior of Low-Ag SAC solder were studied. The effect of adding Bi and Ni elements on the wettability, melting temperature and electromigration properties of SAC0705 (Sn-0.7Ag-0.5Cu) soldering on Cu pad were analysed by SEM and DSC investigations.

Results indicate that addition of some Bi and Ni elements into SAC0705 could decrease the peak melting point of the solder, improve the wettability of solder on Cu pad obviously, and decrease the IMC grain size in interface.

In addition, adding some Bi and Ni elements could restrict the electromigration behavior under high temperature and high density current stressing. It is found that the thermal condition has much more influence on electromigartion behavior. The IMC polarized distribution and copper consumption aggravate sharply under higher temperature and high density current stressing condition"

Sun, F., Liu, Y., Wang, J.

School of Material Science and Engineering, Harbin Uni. of Sci. and Tech., Harbin, China

The creep behaviour and microstructure of ultra small solder joints

Scopus: "The creep behavior of Sn-based solders undergoes a significant scaling effect. Therefore this paper compares creep data that was gained on bulky samples and on small solder joints. Optical microscopy techniques and SEM-microprobe analysis were used to examine the microstructural properties of the bulk specimens and real solder joints were after metallographic sectioning. The results of these microstructural analysis were related to the investigated mechanical properties of the solders"

Low Tm Solder HP

Low Tm Solder: "The application of low-temperature solders in surface mount assembly processes for products that do not experience harshtemperature environments is technically feasible. Low-temperature assembly appears promising as an addition to the surfacemount landscape as a way of increasing process flexibility and component reliability.

However, one single alloy won’t be auniversal solution. Specific component and assembly requirements will have to be considered in choosing or tailoring thebest solder alloy for each application."

Advantages of Bismuth-Based Alloys for Low-Temperature Lead-Free Soldering and Rework

EMS007: "The increased function of personal electronic devices, such as mobile phones and personal music devices, has driven the need for smaller and smaller active and passive components."

This trend toward miniaturization, occurring at the same time as the conversion to RoHS-compliant lead-free assembly, has been a considerable challenge to the electronics assembly industry. The main reason for this is the higher reflow process temperatures required for lead-free assembly. These higher temperatures can thermally damage the PCB and the components. In addition, the higher reflow temperatures can negatively affect the solder joint quality, especially when coupled with the smaller paste deposits required for these smaller components. If additional thermal processing is required, the risk increases even more.

A low-temperature solder is advantageous in this process in that its lower temperature thermal processing requirements can reduce the total thermal damage caused by using higher melting temperature alloys. Defects, such as delamination or "popcorning" of moisture sensitive devices (MSD), could be minimized or eliminated by using lower temperature solders. Delamination or popcorning failure modes occur when moisture diffuses into plastic components that rapidly expand upon heating. These lower temperature alloys may also be considered for use with temperature sensitive components, the step soldering process or rework.

Effect of Ti on the interfacial reaction between Sn and Cu

Scopus: "The effect of Ti on the solid state reactions between Sn and Cu has been investigated in this work.

Based on the experimental results the following statements about the effect of Ti can be made:

Firstly, the presence of Ti does not have measurable effect on the thickness of either Cu6Sn5 or Cu3Sn during solid state annealing. However, the unevenness of both Cu6Sn5 and Cu3Sn layers is increased by the addition of Ti.

Secondly, there is no marked solubility of Ti to either Cu6Sn5 or Cu3Sn. Rather Ti reacts with Sn to form large Ti2Sn3 platelets inside the solder matrix. These findings were subsequently rationalized with the help of the assessed Cu-Sn-Ti phase diagram. By utilizing this phase diagram information, the absence of any marked effects of Ti on the growth of Cu-Sn intermetallic compound (IMC) formation was rationalized. As there is a very low solubility of Ti to SnAg solder and to Cu-Sn IMC's, Ti cannot change activities of components in the solder nor influence the stability of the IMC layers.

Hence, these results throw significant doubts over the concept of trying to influence the Cu-Sn IMC layer thickness or quality by Ti alloying."

Vuorinen, V., Dong, H.Q., Laurila, T.

Electronics Integration and Reliability, Department of Electronics, School of Electrical Engineering, Aalto University, P.O. Box 13000, Aalto, FI-00076, Finland

Toyota hybrid recall

KETK: "The Toyota Highlander and Lexus RX hybrids are being called in for a transistor on a control board in the Hybrid system inverter may have a bad solder.

“And what we have is a circuit board inside what’s called the intelligent power module,” says Brian Lyons of Toyota. “And some of the transistors responsible, there’s a transistor that wasn’t adequately soldered. And it will be damaged during high load and large current flow during driving.”

That’s right. One bad solder that finally gives way and your Lexus will either simply limp home on half power or…
“Uh, coast to a stop,” Lyons said. “I want to clarify, it doesn’t just stop, but yeah, you would lose all motive power.”

The company says, it is a voluntary recall…
“Uh, yes, well, to be precise it’s more of an influenced recall. The federal…NHTSA had begin an investigation into the problem back in February,” according to Lyons.
Owners will get a letter in July and the fix, if necessary, will take about 4 hours.

Although Toyota sales are rebounding finally, the company expects the cumulative effects of both publicity and national disasters to reduce their 2011 profits by one third."

China RoHS documents

Although there has been less exposure on China RoHS in recent days, continuous regulatory work has been and will be done on the subject by the Chinese authorities. Amongst others, the following China RoHS standards have been adopted in May 2011 and will enter into force on 1 August 2011:

Standards on the Requirements of Concentration Limits for Certain Restricted Substances in Electrical and Electronic Products (电子电气产品中限用物质的限量要求: GB/T 26572-2011),

Standards on Electrical and Electronic Products - Measurement of Six Regulated Substances (Lead, Mercury, Cadmium, Hexavalent Chromium, Polybrominated biphenyls, Polybrominated diphenyl ethers) (电子电气产品六种限用物质(铅、汞、镉、六价铬、多溴联苯和多溴二苯醚)的测定: GB/T 26125-2011).

One of the key messages here is that the scope of controlled products will be extended from "electronic information products" to "electrical and electronic products", as it was proposed in the Draft Measures for the Pollution Control of Electrical and Electronic Product" (电子电气产品污染控制管理办法) of 16 July 2010.

As of July 2011, Chinese authorities are working on the following China RoHS standards which would be soon published:

Marking for Control of Pollution caused by Electrical and Electronic Equipment (电子电气产品污染控制标识要求: SJJNXT4304-2010) which would replace SJ/T 11364-2006

Guidance on Risk Assessment for Substances of Certain Hazardous Substances contained in Electrical and Electronic Equipment (电子电气产品中限用物质存在的风险评估指南: SJJNZZ4305-2010)

General Rules on the Screening of Restricted Substances in Electrical and Electronic Equipment - X-ray Fluorescence Spectrometry (电子电气产品中限用物质的筛选应用通则 X射线荧光光谱法: SJJNZT4306-2010)

Application Requirement of Soldering Process for Lead Free Component (无铅元器件焊接工艺适应性要求: SJJNZT4308-2010).

Lastly but not least, the China National Certification and Accreditation Administration will soon publish "Implementation Rule on Certification on Pollution Prevention and Control of Electrical and Electronic Products (电子电气产品污染控制认证实施规则)" which will define details on the certification of electrical and electronic products. [(c) Young & Global Partners]

Solderability of metallic glass

Scopus: "Nishikawa, H., Takemoto, T.
JWRI, Osaka University, Osaka, Japan"

Ecologically clean solder based on Sn-Ag-Cu

Scopus : "A solder is developed, which does not contain harmful components such as lead and shows super performance properties, at the same time the processing behaviour of the solder remains unchanged"

Field Data Encouraging for Lead-Free Solder Reliability

Dr. Lasky's Blog | INDIUM: "'In general, the reliability of lead-free solder is equal or better than leaded solder except for BGA/CSP/WLCSPs. The high silver content in SAC387 resulted in poor drop performance of these packages as the joints are very brittle. This issue can be addressed by reducing the Ag content of the solder balls.'

Being an early adopter, Motorola qualified the near-eutectic SAC387 solder. So, with SAC387 and SAC105 solder balls, Motorola's field data (for about ten years and over 100 million mobile phones) shows equal or better reliability than leaded solder. While these data do not necessarily support other applications, they are encouraging.

Another encouraging thought is that, since its debut (with RoHS now about to celebrate its 5th anniversary), about US$4 trillion of lead-free electronics have been manufactured with no shocking reliability problems."

Bonding nature of rare-earth-containing lead-free solders

Scopus: "The ability of rare-earth-containing lead-free solders to wet and bond to silica was investigated. Small additions of Lu (0.5-2 wt.%) added to eutectic Sn-Ag or Au-Sn solder render it directly solderable to a silicon oxide surface. The bonding is attributed to the migration of the rare-earth element to the solder-silica interface for chemical reaction and the creation of an interfacial layer that contains a rare-earth oxide. It was found that additions of rare-earth materials did not significantly modify the solidification microstructure or the melting point. Such oxide-bondable solders can be useful for assembly of various optical communication devices."

Electronic Products and Technology - Unit recycles 90% solder paste

EP&T : "SEIKA USA Solder Paste Recycling Unit enables approximately 90 percent of waste solder paste to be recovered as solder bar. System provides a major decrease in disposal costs for factory waste, a reduction in CO2 emissions and reduced costs for solder bar as a result of recycling waste. As an additional benefit. Unit is fully automated with the use of a touch screen panel."

European Metal Recycling and Summit Solders

European Metal Recycling: "EMR has a wholly owned subsidiary, Summit Solder Products, who are the leading UK manufacturer of tin based solder products. Our expertise has been developed through understanding each industry and knowing exactly what different customers require. Our reputation has been built through supplying consistently high quality solder products with exceptional levels of customer service.

Using highly efficient technology, we are able to enhance the purity of any alloy, which not only reduces waste for the end user, but also saves on cost."

iNEMI: Book on Lead-Free Solder Process Development

EMS007: "The International Electronics Manufacturing Initiative (iNEMI) is pleased to announce the recent publication of Lead-free Solder Process Development, by Wiley-IEEE Press. Several iNEMI project leaders and participants were involved with this book, which is an important reference guide for engineers in the electronics manufacturing industry who are, or will be, migrating to lead-free soldering.

The book’s editors are Gregory Henshall (HP), chair of iNEMI’s Characterization of Pb-Free Alloys Project; Jasbir Bath (iNEMI consultant), co-chair of the Pb-Free Rework Optimization Project; and Carol Handwerker (Purdue University), co-chair of of iNEMI’s Research Committee. In addition, more than half of the book’s 10 chapters were written or co-authored by iNEMI members, including representatives from Cisco, Delphi, Flextronics, HP and Intel.

The 250-page book covers several key lead-free topics, including legislation, SMT, wave soldering, rework, BGA/CSP component alloys, tin whiskers, testability, mechanical reliability, aerospace/military reliability and automotive reliability. Each subject area is discussed by people who have conducted work in the field and can provide insights into the most important considerations. The book also provides updates regarding ongoing research and development, and addresses new topics that are relevant to lead-free soldering."

Lead-free solder brings many benefits

IPC: "One of the biggest question marks surrounding lead-free solders is their reliability. But Ronald C. Lasky says that it’s difficult to support that perception."

“A lot of people claim that lead free solder is not as reliable as lead-based solder,” said Lasky, an instructional professor at Dartmouth College’s Thayer School of Engineering. “We’re now five years into the implementation of RoHS and we’ve made $3 trillion worth of electronics. We haven’t really noticed any big change in reliability. However, it is clear that we have not established long term reliability, as most of these products have not been deployed that long.”

In fact, lead-free solder has made it simpler to continue the dramatic size reductions that are enabling the great progress and growth in handheld devices. Today’s solders are easier to mass produce when pitches are tight. When high density semiconductors are packaged in small form factors, using lead-free solder can result in boards with fewer problems.

“Lead free solder doesn’t wet well so you can get better lead spacing,” Lasky said. He cited a study by Motorola where designers built identical boards with lead-based and lead-free solder. It showed that leads printed close together shorted out when lead solder flowed during melting.

The high temperatures needed to melt lead-free solder have created some problems.

“Moisture sensitivity is a big issue that’s often overlooked. Much of the moisture research was done for lead-based temperatures, not the higher temperatures of lead-free processes. If you have a moisture rating of four for lead, it might be five or six at lead-free temperatures,” Lasky said. This new situation can cause problems, such as “popcorning” and in addition board warpage.

Major Taiwan IC backend firms developing copper pillar bumping

Digitimes: "Recognized as a key next-generation flip-chip (FC) packaging technology, copper pillar bumping offers cost savings over conventional solder bumping and achieves a higher memory density. Copper pillar is seeing growing adoption among communications-related chips, and will likely be a sales growth driver for packaging and testing firms in 2012."