Thermally superior Nanotapes to replace solder bonding in semiconductor chips

EE Herald: "Researchers from Semiconductor Research Corporation (SRC) and Stanford University have developed a new material for replacing pins and solder pads used in bonding sections of semiconductor devices. This material is less degradable compared to solder pads and also withstands higher heat and mechanical stress. Same technology can also be used in non-semiconductor applications.

This new material offers high thermal connectivity compared to copper and is also with the flexible compliance of foam. The nanostructured tape like shaped material conducts heat like a metal and flexible enough to allow the neighboring materials to expand and contract with temperature changes."

OM520 SnBiAg study

Scopus: "The compliancy with RoHS directives as well as the trend towards green technologies and green processes has been the main driver for the paste manufacturers. One direction that has proven to be worth while exploring is the one towards low melting point alloys that will enable energy savings during the manufacturing processes. Last but not least these emerging alloys will add an extra benefit to the economy of the production process, the elimination of wave soldering process. The solder paste used: OM520, 42%Sn/57.6% Bi/0.4%Ag, type 3 powder by IPC J-STD-005 [7], the study was completed on a FR2 PCB with OSP finish. A SAC305 paste - OM338PT, SAC305, type 3 powder by IPC J-STD-005 [8] - was used as benchmark for the measurements."

Cucu, T.C., Plotog, I., Svasta, P., Branzei, M.

Politehnica University of Bucharest, Romania

Alpha Announces Global Licensing Agreement with Alcatel Lucent for SnBiAg Lead-Free

Factiva: "Alpha announces that it has established a licensing agreement with Alcatel Lucent to complete Alpha’s suite of global sub-licenses required to offer SnBiAg low temperature solder paste to the global Electronics Assembly Market.

‘Cookson Electronics is a strong supporter of Intellectual Property rights for both our internally developed technologies, and for technologies developed by others,’ said Bruce Moloznik, Alpha’s VP - Global Marketing & Corporate Development. ‘Alpha’s recent agreement with Alcatel Lucent completes our global patent access to the SnBiAg alloy technology and its associated global IP landscape.’

Alpha has engineered its CVP-520 SnBiAg lead-free solder paste based on this intellectual property and will continue to utilize the SnBiAg alloy in the development of other soldering products that will produce electronic joints with higher reliability than those produced using eutectic SnBi alloys. With this increased reliability, Alpha’s SnBiAg products will enable the use of a low temperature second-side reflow process that can eliminate wave soldering of many multi-technology electronic assemblies that still require wave soldered joints.

With the higher reliability of Alpha’s CVP-520 SnBiAg solder paste over eutectic SnBi pastes, many electronics assemblers may also be able to take advantage of lower energy and material costs enabled by a 20% lower reflows peak temperature versus traditional SAC 305 processes."

Transition to Lead-Free Products in the US Electronics Industry: A Model of Environmental, Technical, and Economic Preferences

Scopus: "The European Union's Restriction on the Use of Certain Hazardous Substances (Directive 2002/95/EC) targeted at electronic products took effect in 2006. In contrast, the USA has no comparable national policy on these products. To understand corporate responses to policy differences across jurisdictions, we conducted a structured-questionnaire survey of individuals in 109 companies that are representative of the US electronics industry. The results reveal that 70% of these companies have already adopted lead-free solder for electronics with 49% of the total preferring the SnAgCu formulation, despite uncertainties associated with environmental impacts of this alternative alloy. We use a modified life cycle impact assessment method based on endpoint modeling approach to derive weighting factors that represent the respondents' value system for tradeoffs among environmental impacts. We use a modified fuzzy Technique for Order Preference by Similarity to Ideal Solution approach to evaluate technical criteria dominance in declared preferences. A statistical model of corporate behavior is also presented. The results provide the first systematic framework that accounts for environmental impact, technological challenge, and business strategy concurrently toward formulating a comprehensive national policy for materials selection in electronic products"

Alpha awarded China patent for its SACX Plus Solder Alloys

Global SMT and Packaging: "Alpha announces that the patent for its SACX Plus solder alloys has been formally granted by the Chinese State Intellectual Property Office. Use of any of the ALPHA SACX Plus alloys in a soldered connection is covered by this patent. Alpha's covered alloys include: SACX Plus 0807, SACX Plus 0307, SACX Plus 0107 and SACX Plus HASL.

'We have made a significant investment in the development of our SACX Plus family of alloys with the intention of providing high value lead-free solder options to assemblers, and we are pleased that China has joined other countries in recognizing their uniqueness,' said Mike Murphy, Alpha’s Global Product Manager for Wave Soldering Materials. 'Our ALPHA SACX Plus alloys perform similar to SAC305 on more complex assemblies while offering superior performance over SnCu alloys on simpler boards, all at a cost closer to the price of SnCu alloys.'"

The Debate: Will Plated Copper Vias Replace Solder?

EMS007: "The Motion calls for ultimate replacement of most solder joints by electroplated copper, but that statement is deceptively simple. SMT solder joints are reflowed in a plane, but electroplated copper joints would require embedded components whose leads or terminals would be accessed by vias that are subsequently plated. That would represent a shift from two to three dimensions for electronic PCB component interconnections. The new manufacturing paradigm would also completely replace today's electronic manufacturing plant and supply chains. That is what the debate is really about."

What's Wrong with Pb Joint Test Reliability Requirements?

EMS007: "Mr. Reliability, Werner Engelmaier, talks with SMT Magazine Publisher Ray Rasmussen about the current test requirements for solder joint reliability. The IPC Product Reliability Committee Co-Chairman says the requirements don't match real-world conditions. A disconnect exists between what OEMs require and what companies can produce."

http://www.pcb007.com/radio/werner.htm

Effects of bulk Cu6Sn5 intermetallic compounds on the properties of Sn-Ag-Cu-Ce soldered joints

Scopus: "In addition, based on finite element simulation, it is found that the von Mises stress concentrate around the bulk Cu6Sn5 IMCs inside the Sn-Ag-Cu-Ce soldered joints after three thermal cycling loading (255-125'C). From the stress distribution, the failure site was predicted to fracture near the bulk Cu 6Sn5 IMCs interface. This coincides with the experimental findings significantly"

Zhang, L.a , Xue, S.-B.a , Gao, L.-L.a , Sheng, Z.a , Dai, W.a , Ji, F.a , Ye, H.a , Chen, Y.b , Yu, S.-L.a c

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

b Harbin Welding Institute, Harbin, China

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

Al2O3 in SnZn solders

Factiva: "Nano-sized, nonreacting, noncoarsening Al2O3 particles have been incorporated into eutectic Sn-Zn solder alloys to investigate the microstructure, hardness and shear strength on Au/Ni metallized Cu pads ball grid array substrate (BGA). In the plain Sn-Zn solder joint and solder joints containing Al2O3 nano-particles, a scallop-shaped AuZn3 intermetallic compound layer was found at the interfaces,' scientists in Hong Kong, People's Republic of China report.

'In the solder joints containing Al2O3 nano-particles, a fine acicular-shaped Zn-rich phase and Al2O3 nano-particles were found to be homogeneously distributed in the beta-Sn matrix. The shear strengths and hardness of solder joints containing higher percentage of Al2O3 nano-particles exhibited consistently higher value than those of plain solder joint and solder joints containing lower percentage of Al2O3 nano-particles due to control the fine microstructure as well as homogeneous distribution of Al2O3 nano-particles acting as a second phase dispersion strengthening mechanism"

Fouzder and colleagues published their study in Microelectronics Reliability (Effect of nano Al2O3 additions on the microstructure, hardness and shear strength of eutectic Sn-9Zn solder on Au/Ni metallized Cu pads. Microelectronics Reliability, 2010;50(12):2051-2058).

For additional information, contact Y.C. Chan, City University of Hong Kong, Dept. of Electrical Engineering, Tat Chee Avenue, Kowloon Tong, Hong Kong, People's Republic of China.

SAFE: A Brief History of Solder in Electronic Assembly

EMS007 : "In summary, the soldering process is complex and has been an important method for making electronic assemblies. Its use will continue because the present manufacturing infrastructure is set up for its use. However, like everything, the soldering process has its limits and its reliability is being called increasingly into question with the use of lead-free solder. Suggesting that reduced reliability does not matter because product life cycles are being shortened does not appear to be well aligned with the increased interest in creating an industry that is more sensitive to environment and the needs of the world's poorest consumers."

Investigation of the effect of indium addition on wettability of Sn-Ag-Cu solders

Scopus: "Taking into account the contact angle data from the WB and SD methods, the best results of the SAC-In alloy on copper were obtained for the alloy of the highest In content. It was found that the contact angles from SD after 4 s were higher (non-equilibrium conditions) than the values calculated from WB after 3 s. In contrast, the contact angles from SD after 10 min (equilibrium conditions) were lower than those from WB after 3 s. The comparison suggests that the contact angles from WB are situated within the data from SD, showing the same lowering tendency with the increasing content of In, and they may be well accepted for practical purposes. On the other hand, the sample of the solder in the SD method, after a prolonged time - in order to get the equilibrium contact angle - may be used to study the interfacial phenomena with the Cu substrate. The differential thermal analysis results indicate that the melting temperature decreases with increasing tin concentration. Taking into account the results of this study and the available literature data, alloys containing 8-10 wt% of In can be recommended for practical application."

No finish for lead-free issues

EMSNow: "It's been well more than a decade since regulators banned lead from solder, but designers in many fields are still grappling with quality issues that rippled out from the changeover. Most of today's problems are subtle issues that only impact some designs, but those concerns are not minor for those that have quality issues.

'People are still struggling with certain areas in the lead-free arena,' said Cheryl Tulkoff, CRE senior member of technical staff at DfR Solutions LLC of Austin, Texas. 'One area is in PCB finishes, where standbys like immersion tin and ENIG aren't always suitable and newer techniques like lead-free HASL have picked up steam but have still issues with planarity and availability.'"

Preparation and thermal analysis of Sn-Ag nano solders

Scopus: "In this study, Sn-Ag nano solders of three different compositions (Sn-1.0mass%Ag, Sn-3.5 mass%Ag and Sn-6.5 mass%Ag) were synthesized via arc-discharge process. The properties of Sn-Ag nano solders were analyzed using X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX), and Differential Scanning Calorimetry (DSC). Particle size relatively widely ranged from 10 nm to 340 nm. For Sn-1.0mass%Ag and Sn-3.5 mass%Ag, average size was 200∼240nm, and that for Sn-6.5 mass%Ag was 40∼50nm with some extra-ordinary large particles of ∼100nm. The melting points of the prepared SnAg nano solders were examined with DSC at different heating rates 1K, 3 K and 5 K/min. The congruent melting point of Sn-Ag nano solders was found to be 487 K"

Printable electronics: Towards materials development and device fabrication

Scopus: "There has been increasing interest in the development of printable electronics to meet the growing demand for low-cost, large-area, miniaturized, flexible and lightweight devices. The purpose of this paper is to discuss the electronic applications of novel printable materials. Design/methodology/approach - The paper addresses the utilization of polymer nanocomposites as it relates to printable and flexible technology for electronic packaging. Printable technology such as screen-printing, ink-jet printing, and microcontact printing provides a fully additive, non-contacting deposition method that is suitable for flexible production."

Effect of Ag content on mechanical properties of lead-free Sn-Ag-Cu-Ni-Ge alloy

Scopus: "The tensile properties of Sn-x(x=1, 2, 3)Ag-0.5Cu-0.05Ni-0.005Ge (mass%) alloys were investigated. In addition, the ball shear force was investigated with solder balls and two types electrodes, Cu and electroless Ni/Au plated Cu, to examine joint reliability under heat exposure conditions. Tensile strength of the alloy decreases with decreasing the Ag content. On the contrary, elongation increases with decreasing the Ag content. When the Ag content reduces, primary β-Sn phases are coarsened and eutectic microstructures diminish. The decrease of the eutectic microstructures causes a reduction of the tensile strength. In as-soldered joints with Sn-Ag-Cu-Ni-Ge solder balls and Cu electrodes, the ball shear force increases with increasing the Ag content. However, the ball shear force decreases with increasing heat exposure time. After heat exposure treatment at 423 K for 500 h, the ball shear force is relatively stable at lower values regardless of the Ag content. In the joints with electroless Ni/Au plated Cu electrodes, the ball shear force slightly increases with increasing heat exposure time. Even after heat exposure treatment at 423 K for 500 h, hierarchy of the ball shear force is maintained. The ball shear force becomes high with increasing the Ag content."

Effect of interfacial reaction in Sn-Ag-Cu solder alloy with Ni addition

Scopus: "Sn-Ag-Cu-Ni-Ge solder alloy has been developed to improve the mechanical properties of the Sn-Ag-Cu base solders and prevent oxidation of those solders. In this paper, an interfacial reaction and microstructure between the solder and a Cu electrode were investigated under heat exposure conditions. It was found that intermetallic compounds growth at the interface of the solder and the Cu electrode was greatly affected by amounts of added elements. Adding Ni in the solder can suppress the formation and growth of intermetallic compounds (IMCs) such as Cu-Sn and decreasing the amount of adding Ag in the solder can prevent the formation and growth of Ag3Sn. Moreover, it was found that there was an effect of suppress the growth of the Cu3Sn formed on the interface of Cu and (Cu,Ni)6Sn5 by adding Ni from analysis results of EDX and TEM"

Thermal fatigue endurance of Sn3Ag0.5Cu0.5In0.05Ni and Sn2.5Ag0.8Cu0.5Sb solders in composite solder joints of LTCC/PWB assemblies

Scopus: "The purpose of this paper is to investigate the thermal fatigue endurance of two lead-free solders used in composite solder joints consisting of plastic core solder balls (PCSB) and different solder materials, in order to assess their feasibility in low-temperature cofired ceramic (LTCC)/printed wiring board (PWB) assemblies."

Package-on-Package (PoP) Solder Paste

INDIUM: "A 400micron bump should therefore be fine even with a type 3 dipping paste, whereas a 200micron bump will need a type 5 paste.

I look forward to someone proving this wrong. The second (ii/) is helpful, because we can easily use it to test the theoretical mass of PoP dipping paste against what we actually find. Note that this is just simple geometry: it doesn't tell us how much paste is really needed to resolve issues such as the 60 - 90micron bowing we are hearing about from our customers even with the more rigid PoP packages currently available. I will be talking more about this at the"

INVENTEC Performance Chemicals to present paper on Solder Paste Residue Corrosivity Assesments

EMSNow: "INVENTEC Performance Chemicals to present paper on Solder Paste Residue Corrosivity Assesments during IPC Conference on Quality, Reliability & Acceptability for Electronics Assembly at Budapest, Hunagry February 24th.

INVENTEC's Global Applications Manager, Ms. Emmanuelle Guene, will present the most recent finding in solder paste residues corrosivity by appication of different measuring tests such as THB and Bono Test. It has been proven that compared to common corrosion tests, the Bono test better diffentiates the nature of solder paste residues. This can be attributed to many factors: board design, tests conditions and the applied bias"

In Search of Tin Whisker Fails in Lead-Free Soldering

Dr. Lasky's Blog | INDIUM: "So here is my question, who knows of any verified tin whisker fails when tin whisker mitigation techniques where used? Tin whisker mitigation techniques typically use 2% bismuth or antimony in the tin, assure that the tin has a matte finish and use a nickel strike plating between the copper and the tin to minimize copper diffusion into the tin.

Surely if tin whiskers are a major concern, there should be many fails in the over $3 trillion worth of RoHS compliant electronics manufactured since July 2006."

NASA Exonerates Toyota's Electronics But Indicts Tin Whiskers

PCB007: "The investigation provided new insight into another problem that goes far beyond Toyota to the entire global electronics industry. It is summarized in the following table from the NASA report. In using L-F solder, Toyota was just being a good citizen, complying with a EU mandate known as ROHS that forbids the use of lead. The result has been the imposition of enormous cost, environmental damage, and increased energy consumption on the world. Now the NASA report shows that all electronics reliability is also threatened."

Lead free solder development and analysis for aerospace applications

Oxford Materials - Personal Homepages: "Due to safety considerations, the aerospace industry is largely exempt from legislation prohibiting the use of lead in interconnects in electronic assemblies, and lead continues to be used in avionics. This situation is unlikely to continue because of further legislation and difficulties in sourcing lead-containing materials and assemblies from suppliers. In contrast to domestic electronics where lead free solders are now standard and reliable, there are no current widely accepted 'drop-in' replacement materials for lead solders that meet the more stringent and hostile aerospace standards for reliability. There is now a pressing need to develop underpinning scientific understanding of the factors governing lifetime of existing and future lead free solder materials for critical aerospace applications"

SMART Group Announces Two (FREE) Webinars Covering New EU Projects

EMSNo: "uBGA European Project Update
Tuesday 19th April 2011 at 14.30 GMT

There is relentless consumer demand for electronics equipment offering miniaturisation with higher functionality (e.g. cell phones playing music and movies whilst also offering email/SMS/camera functions). The industry is therefore continuously aiming for increases in integrated circuit miniaturisation, processor speeds and circuit densities. A major interconnection and a vital part of package manufacture for reliable connection is provided by the solder sphere."

This uBGA project will re-evaluate existing manufacturing process, inspection and size control of different solder alloy spheres. It will then produce example packages and demonstrate the reliability through assembly and soldering trials within different industries. If you want an insight into the future of uBGA manufacture and the problems being researched join us for this webinar.

Topics will include:

Project overview, Industry survey, uBGA requirements, solder alloy requirements, solder sphere manufacture, existing process & issues and conclude with future industry benefits.

μBGA is a collaboration project, co-ordinated and managed by KCC Ltd and is partly funded by the EC under the Research for the Benefit of Specific Groups Project ref: FP7-SME-2002-2-GA-263653

BIZESP links with ChinaTin

London Hackspace Open Day | Londonist

Londonist: "Don’t be put off by the name. London Hackspace isn’t just for coding nerds. It’s a place where anyone of a crafty bent can tinker, tailor, solder and sew – a non-profit, community-run space where ‘people who make things can come to share tools and knowledge’. It’s a bit like in the A Team, when the once-again-incarcerated foursome would build an armoured vehicle out of a mattress and a toilet brush…but without Colonel Decker’s armed goons guarding the entrance."