Low silver mechanical properties

Factiva: "In this study, bulk solder tensile tests were performed to characterise the mechanical properties of SAC 105 (Sn-1%wt Ag-0.5%wt Cu) and SAC 405 (Sn-4%wt Ag-0.5%wt Cu) at strain rates ranging from 0.0088 s(-1) to 57.0 s(-1).

Solder joint array shear and tensile tests were also conducted on wafer-level chip scale package (WLCSP) specimens of different solder alloy materials under two test rates of 0.5 mm/s (2.27 s(-1)) and 5 mm/s (22.73 s(-1)). These WLCSP packages have an array of 12 x 12 solder bumps (300 mu m in diameter); and double redistribution layers with a Ti/Cu/Ni/Au under-bump metallurgy (UBM) as their silicon-based interface structure.

The bulk solder tensile tests show that Sn-Ag-Cu alloys exhibit higher mechanical strength (yield stress and ultimate tensile strength) with increasing strain rate. A rate-dependent model of yield stress and ultimate tensile strength (UTS) was developed based on the test results. Good mechanical performance of package pull-tests at high strain rates is often correlated to a higher percentage of bulk solder failures than interface failures in solder joints."

V.B.C. Tan, Singapore National University, Dept. of Mech Engineering, 9 Engineering Dr. 1, Singapore 117576, Singapore.

Low processing temperature of lead-free solder interconnects

Scopus: "The thermal properties of tinsilvercopper SnAgCu alloy nanoparticles of different sizes were studied by differential scanning calorimetry DSC. The particle size-dependent melting point and latent heat of fusion were also observed. The nanoparticle pastes completely melted and wetted on the copper surface, and tincopper intermetallic compounds IMCs were formed after the reflow process. These low-melting-point SnAgCu alloy nanoparticles pastes could be used for low processing temperature of lead-free solder interconnect applications."

Jiang, H.a , Wong, C.P.b

a Intel Corporation, Chandler, AZ, United States

b School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, United States

Henkel acquires solder sphere manufacturer, Accurus Scientific Company Ltd.

EMSNow: "Upholding its promise to deliver customers with single-source materials solutions for the entire semiconductor packaging and printed circuit board (PCB) assembly value chains, Henkel today announced that it has successfully acquired Accurus Scientific Co. Ltd.. The Taiwan-based Accurus Scientific Co. Ltd. is a leading manufacturer of solder spheres and type 1 through type 7 solder powders with 170 employees. It is an ISO 9001 and ISO 14001 certified company.

'The addition of Accurus to our portfolio brings Henkel's product offerings full circle - enabling us to provide complete materials solutions, which now includes advanced solder sphere technology for next-generation CSP and BGA devices and specialty solder powder for fine-pitch applications,' says Dr. Jochen Krautter, Executive Vice President of Henkel Technologies"

Foxconn moving from southern China to northern and western regions, says report

EMSNow: "The Foxconn Group, after announcing wage hikes for employees at two production bases in Shenzhen, southern China in early June, has been shifting a large portion of the production lines from Shenzhen to its production bases in Tianjin, northern China, and Wuhan and Chongqing, western China, according to a Chinese-language China Times report.

The two production bases in Shenzhen currently have 400,000 employees in total and will be combined into one, with only a few relatively profitable production lines to remain, the report pointed out. As the minimum monthly wages in Tianjin and Wuhan are currently 920 yuan (US$135) and 900 yuan respectively, the moves are to reduce labor costs because Foxconn may not raise wages for workers in the two places, the report analyzed. According to other China-based reports, Foxconn began to stop recruiting new employees in Shenzhen on May 29."

Effects of cerium content on wettability, microstructure and mechanical properties of Sn-Ag-Ce solder alloys

Scopu: "We investigated the effects of adding small amounts of cerium (Ce) to low Ag content Sn solder (Sn-1.0 wt.%Ag) on melting temperature, microstructure, wettability and mechanical properties using differential scanning calorimeter, optical microscope, scanning electron microscope, energy dispersive X-ray spectroscopy, wetting balance tester, Vickers hardness tester and tensile tester assays. The addition of Ce had little influence on the melting behavior of Sn-1.0Ag solder, but improved its wettability, mechanical properties, and microstructure"

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

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

Reliability testing and damage analysis of lead-free solder joints: New assessment criteria for laboratory methods

Scopus: "Detailed electric and mechanical testing as well as metallographic cross-section analysis of differently aged specimens soldered with standard SnPb and lead-free SnAgCu-solder revealed advantages and disadvantages of commonly used examination methods. The gained experiences are used to develop an approach for a new test series. The goal is to develop quantitative measures for damage analysis of solder joints via new testing methods and more elaborate examinations of common methods. On the basis of these measures a more distinct correlation of failure modes to loading conditions shall be possible."

a Volkswagen Laboratory Metals, Letter Box 1437, 38436 Wolfsburg, Germany

b Electronic Packaging Laboratory, Dresden University of Technology, Germany

c Technology Development, Hella KGaA Hueck and Co, Germany

SMTA International

SMTA: "HE1 Pb-Free Technology Insertion
Chair: John Evans, Ph.D., Auburn University
Co-Chair: Heather McCormick, Celestica Inc.
Monday, October 25
8:00am – 9:30am, Oceanic 7

The Pb-free (Lead-free) in Electronics Risk Mitigation (PERM) Consortium
Anthony Rafaneiil, Raytheon Integrated Defense Systems
Overview of the New DoD Reliability Revitalization Initiatives
James McLeish, CRE, DfR Solutions; Grant R. Schmieder, CRE, Defense Research and Engineering
Transition to Lead Free Production for Avionics, Steps Forward Along a Lead Free Control Plan and Further Requirements
Michael Jeremias, EADS Deutschland GmbH"

IPC Electronics Symposium to highlight RoHS revisions

EMSNow: "To help companies understand new laws, regulations and regulatory trends, IPC will hold an IPC Symposium on Electronics and the Environment on July 19-21, 2010, in Boston, Mass.

Increasingly, these regulations are affecting every level of the electronics manufacturing supply chain. Symposium speakers represent companies such as Dow Electronic Materials, Celestica, Texas Instruments and Design Chain Associates.

Workshops are scheduled preceding and following the symposium. On July 19, the workshop, Understanding the Fundamentals of the REACH Regulation, will provide a 'soup to nuts primer that will serve as foundation for the symposium on July 20-21. On July 21, Understanding and Implementing IPC-1752A on Materials Declaration will cover new revisions to this industry standard for materials content data and will help attendees implement the changes in their companies."

PCB Book-to-Bill Up Again in May

Surface Mount Technology: "“Both yearly and monthly growth rates in the North American PCB industry are now positive,” said IPC president & CEO Denny McGuirk. “That means the industry is not only doing better than last year, but is growing monthly as well. Despite strong sales,” he added, “orders are growing even faster. That keeps moving the book-to-bill ratio up, which indicates continued sales growth this year.”"

Tensile properties of Sn-10Sb-5Cu high temperature lead free solder

Scopus: "The tensile strength of the solder joint decreased after some aging time. However, the strength remained at about 80 % of the original value after aging for 15 days at the temperature of 150'C. The difference in the tensile properties between bulk solder and solder joint resulted from the difference in microstructures. Coarser Cu6Sn5 IMC in the bulk solder led to the higher ultimate strength, and the finer Cu 6Sn5 IMC in the solder joint resulted in much better fracture ductility of the solder joint."

IMAPS 2010, Raleigh/RTP

IMAPSs: "The 43rd International Symposium on Microelectronics will be held at the Raleigh Convention Center, Research Triangle, North Carolina, USA, and is being sponsored by the International Microelectronics And Packaging Society (IMAPS). IMAPS 2010 will feature technical tracks on 3D Packaging/Interconnect, Design, Reliability, Advanced Packaging and Material."

Nanjing University Nd in SAC

Factiva: "Effects of rare earth Nd on solderability of the Sn3.8Ag0.7Cu alloy were studied by wetting balance method, and the mechanical properties (such as pull-force and shear-force) of the joints soldered with SnAgCu-XNd solders were determined using STR-1000 joint strength tester. Moreover, the microstructures of SnAgCu-XNd solders bearing different amount of Nd as well as the intermetallic compounds (IMCs) formed at solder/Cu interface during soldering have been investigated using optical microscopy, scanning electron microscopy and energy dispersive X-ray analysis, respectively.'

'The results indicate that trace amount of Nd addition can remarkably improve the solderability and mechanical properties of SnAgCu solder. At the same time, it is found that rare earth Nd in SnAgCu solder could refine and improve microstructure of the solder, some bigger IMC plates in SnAgCu solder were replaced by fine granular IMCs. Moreover, the thickness of the intermetallic layer at the Cu/solder interface was reduced significantly,' wrote L.L. Gao and colleagues, NanJing University.

The researchers concluded: 'In summary, we suggest that the most suitable content of rare earth Nd is about 0.05 wt% and it will be inadvisable when the Nd exceeds 0.25 wt%.'"

State University of New York Sn crystal studies

Factiva: "The microstructure and Sn crystal orientations of lead-free solder alloys such as near-eutectic SnAgCu have a significant influence on the mechanical response of a solder joint to service conditions. Thus solidification processes were examined in SnAgCu solder joints,' scientists in the United States report.

'Distinct evidence of sixfold cyclic growth twinning of Sn during solidification from the melt was observed in Sn-Ag, SAC and Sn-Cu solders. Three orientations of Sn grains, each having a common < 1 0 0> direction, were found in each of these systems, though the morphologies of these cyclic twinned microstructures differed. Analysis of dendrite arm spacing in cyclically twined structures with a beach ball morphology implies that the common < 1 0 0> axis intersects with the region of the nucleation event. Models are presented for two pseudo/metastable hexagonal unit cells based upon {1 0 1} or {3 0 1} twins that introduce the cyclic twinning structure at the nucleation stage. Formation of these hexagonal unit cells may be facilitated by the presence of alloy elements,' wrote L.P. Lehman and colleagues, State University of New York.

The researchers concluded: 'Subsequent epitaxial growth of the tetragonal unit cell on this nucleus can account for all three types of morphologies observed in microstructures of Sn-rich solder alloys.'"

Nanjing University Ce in SnZn

Factiva: "The influences of different Ce content on the properties of Sn-9Zn lead-free solder were investigated. The results indicate that Ce plays an important role not only in the structure and the solderability, but also in the interfacial structure of Sn-9Zn-xCe/Cu and mechanical property of soldered joint,' scientists in Nanjing, People's Republic of China report.

'Sn-9Zn-0.08Ce shows finer and more uniform microstructure than Sn-9Zn, and when the quantity of Ce is 0.5-1 wt%, some dark Sn-Ce compounds appear in the solder. With the addition of 0.08 wt% Ce, the solderability of solder is significantly improved because the surface tension of molten solder is decreased. Adding Ce makes the Cu5Zn8 IMCs formed at the interface of solder/Cu become much thicker than that of Sn-9Zn/Cu because much more content of Zn diffuse to the interface of solder/Cu to react with Cu. also indicate that adding 0.08 wt% Ce to the solder enhances mechanical property of soldered joint,' wrote W.X. Chen and colleagues, NanJing University."

Beijing University POSS nanocomposites

Factiva: "'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,' scientists writing in the Journal of Materials Science - Materials in Electronics report.

'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 mu m and from 0.54 to 0.32 mu m, respectively,' wrote F. Tai and colleagues, Beijing University of Technology.

The researchers concluded: 'The refined Ag3Sn IMCs, acting as a strengthening phase in the solder matrix, could enhance the microhardness of the composite solders.'"

Video shows the benefits of solder jet printing

EMSNow: "Among the many benefits highlighted by end users in the videos is the ability of solder jet printing to provide independent control over solder paste volume on a pad-by-pad basis. This means, for example, that even boards with a dense mix of fine-pitch and large SMD components, which are virtually impossible to print with using conventional stencil technology, can be handled with ease using the MY500.

Other users highlight the benefit of the MY500 to help with assembly of package on package components, intrusive reflow of connectors as well as BGA upgrades on already assembled product. With the latest release of software now allowing for multilevel boards with editable jetting height, affording you even more flexibility to jet into a cavity or jet on a PCB with already premounted components"

Intermetallics: Modeling the failure of intermetallic/solder interfaces

Scopus: "To understand better the phenomenon, a thermo-electric finite element analysis has been conducted to predict the electrical concentration and joule heating effects on the failure of Sn-2.5Ag-0.8Cu-0.5Sb solder under different applied current densities. The temperature and current density distribution in a solder joint with a crack that propagates near the interface of the bulk solder and intermetallic layer has been predicted. Pronounced temperature and electrical current concentration are observed near the crack tip.

Although the Pb-free solder is usually regarded as having a higher melting temperature compared with traditional Pb-Sn eutectic solder, the concentration of heat at the crack tip caused by joule heating may still melt the solder material under high current density stressing."

Development of lead-free solder alloy certified reference materials (JSAC 0131-0134) for X-ray fluorescence analysis

Scopus: "The Japan Society for Analytical Chemistry has developed a series of certified reference materials (CRMs) for the X-ray fluorescence analysis of Ag, Cu, Pb, and Cd in lead-free solder alloys, named JSAC 0131-0134.

In order to prevent oxidations within the process of fusion, the surfaces of samples were covered by a reducing agent. Furthermore, in order to make a fine metallographic structure, the samples at fusion were quickly cooled by water. By using these new methods, homogeneous samples could be prepared. The concentrations of the four elements ranged from 0.488 to 3.91 mass% for Ag, 0.102 to 1.01 mass% for Cu, 13.9 to 2007 mg kg-1 for Pb, and 0(3)

China releases draft guidance for chemicals notification

Chemical Watch: "The Chinese Environment Ministry has published revised draft guidance to accompany changes to its law on the Environmental Management on New Chemical Substances. The Ministry's Pollution Control Division is inviting comments on the draft guidance by 1 July. The law, which comes into effect in October, brings in major changes to the notification of new chemicals such as classifying them according to the UN Globally Harmonised System (GHS) on the..."

Characterisation and Optimisation of Innovative Solders for Transient Liquid Phase Bonding and Active Soldering

Wiley InterScience: "Hybrid microstructures, able to combine the different properties of metallic and ceramic materials, are a source of growing interest in the field of microsystem engineering. Besides the construction technique, the joining technique plays a crucial role within this framework. Two innovative bonding technologies have been investigated: Transient Liquid Phase (TLP) Bonding and Active Soldering. New solders have been developed, evaluated and characterized with regard to fundamental parameters for the microstructures."

E. Lugscheider, S. Ferrara *

Materials Science Institute, Aachen University, Jülicher Straße 344a, 52070 Aachen, Germany

email: S. Ferrara (ferrara@msiww.rwth-aachen.de)

Nanosilver should not be used in consumer products, says German institute

Chemical Watch: "Manufacturers should not use nanosilver in consumer products such as textiles, food or cosmetics until potential health risks can be ruled out, says the German Federal Institute for Risk Assessment (BfR).

The institute says there is a need for research 'to elucidate the fundamental issues in conjunction with the use of nanoscale silver as an antimicrobial material' such as on what scale do consumers come into contact with nanoscale particles, and how big is the danger of resistance development.

It recommends refraining from using any nanosilver in consumer products until a 'definitive' safety assessment becomes available. It also points that although silver is approved as a dye for food (E174), all nanoscale additives, including nanosilver, require approval for use in food and such approval has not been granted for nanosilver"

Solidification and wetting behaviour of SnAgCu solder alloyed by reactive metal organic flux

Emerald:: "Abstract: Purpose – The purpose of this paper is to develop a new alloying method for solders by using a metal organic modified flux in solder pastes."

Design/methodology/approach – This paper presents the impact of six metal organic compounds (Co, Fe, Al; stearate, oxalate, citrate) on the melting and solidification behaviour in comparison to the revealed microstructure.

Findings – It could be shown that Co and Al influence the supercooling whereas Fe exhibits no effect. Co reduces the supercooling of the cast of about 10?K and affects the nucleation. Al retards the solidification up to 185°C. Doping of the solder by flux containing metal organic compounds is successful and the alloying elements Co and Fe are found in the microstructure.

Research limitations/implications – This paper provides a starting-point for the new alloying method – so far only fluxes for solder pastes have been investigated.

Originality/value – The reactive alloying method enables the use of new alloying elements for solder pastes in unmodified soldering processes.

Tin Whiskers on Component Leads

Circuitmart: "Tin Whiskers on Component Leads
Phil Welcome to board talk. This is Phil Zarrow and Jim Hall, pick and place of the assembly brothers. Sometimes known as ITM consulting consultants. Today we've got an interesting one from an aerospace guy."

Jim

This question is from EB. We work with an aerospace manufacture on PCB assembly that includes lead free components, but no BGA's. We process using tin lead 60/40 solder. But this does not solve the issue with tin plating on the leads and the risk of tin whiskers. According to information on the nasa.gov whisker website (http://nepp.nasa.gov/whisker/), tin whisker formation is an issue on the exposed component leads outside the solder region.

Is there a process that can be used to re-plate component leads to add lead? Well, this is a very common topic which we discuss regularly in our technical workshops entitled lead free for the excemptee where we have people dealing with backward compatibility.

Phil

Typically your brethren from aerospace military avionics, medical, and all you other guys. I thought you were going to get it easy when you didn't have to comply with lead free but we've found just the opposite.

Jim

The NASA website is absolutely correct. When you solder tin plated leads, even matte tin over nickel, the solder cannot be counted on to wick all the way up the lead so you end up with a small section of lead close to the component body that still has tin coating on it. And it can cause whiskers.

If you look at the INEMI (http://www.inemi.org) recommendations for surface finishes, they say that matte tin over nickel is acceptable, it's all under the caveat not for high-rel applications.

Phil

That’s right, so Jim, what’s an engineer to do?

Jim

The standard procedures are affectionately called strip and dip. Basically a chemical or a metallurgical process is used to remove the tin coating and replace it with a tin lead coating. Some use chemistry and acids to strip the tin off and then usually they dip it to replace it. Some use sequential dips in a tin lead pots so each time you dip it you get a purer and purer tin lead coating on the leads. The bottom line is you end up with all of the lead completely coated with tin lead.

Phil

This has become quite a little bit of a cottage industry.

Jim

If you’re doing a significant volume, there's automated equipment you can buy to do this yourself.

Phil

Well, great, that hopefully answers EB's question. This had been Jim Hall and Phil Zarrow, the assembly brothers. Talking to you on board talk and we thank you. Keep those questions coming in. And whatever you do in the meantime ...

Microstructural Analysis of Reballed Tin-Lead, Lead-Free, and Mixed Ball Grid Array Assemblies Under Temperature Cycling Test

Scopus: "For the same component type, the reballed BGA assemblies showed similar temperature cycling reliability regardless of the reballing methods. However, the temperature cycling reliability of the reballed assemblies was worse than that of the mixed and the lead-free assemblies. The mean cycles-to-failure of the mixed assemblies was larger than or equal to that of the lead-free assemblies.

Failure analysis revealed that the failure site in reballed Sn-Pb assemblies was located in the bulk solder at the component side regardless of the component type and the reballing method, indicating that the reballing method did not influence the crack propagation in reballed assemblies. The mixed assemblies had the same failure site as the lead-free assemblies, i.e., in the bulk solder at the component side. The microstructure differences between the tin-lead, lead-free, and mixed assemblies are also discussed in detail"