Keynote Speaker 5
Keith Sweatman
Senior Technical Advisor
Nihon Superior Co., Ltd
Osaka, Japan
Keith is a graduate in metallurgical engineering from the University of Queensland who has accumulated 50 years of experience in soldering technology and, in particular, the soldering processes used in electronics manufacturing as they affect quality and reliability. He began this involvement with soldering technology with the International Tin Research Institute (ITRI), which was a pioneer in the establishment of a scientific basis for what has been the art and craft of soldering. As a result of the reputation that he developed in his work with the ITRI he was hired by the UK-based Multicore Solders Ltd as Technical Manager for their operations in Asia and Australia, eventually rising to the position of Asia Pacific Region Managing Director, where he was responsible for the development of the group’s manufacturing, marketing, technical support, research and product development in the region. When Multicore Solders was purchased by the German Henkel Group Keith moved to the position of Senior Technical Advisor with the Japanese manufacturer of electronics assembly materials, Nihon Superior Co., Ltd. In that role he was closely involved in the transition of the global electronics manufacturing industry to lead-free technologies, and, in particular, establishing a place in that technology for the Nihon Superior “SN100C” lead-free solder. To provide a stronger scientific case for SN100C, Keith turned to University of Queensland and as a result of the success of their research work, Nihon Superior established an ongoing relationship with that university, which has resulted in Keith’s appointment to an Adjunct Senior Fellow position.
Title of the talk
Low Temperature Soldering – A new challenge in electronics assembly
Abstract
Just as the electronics industry is getting comfortably settled into the use of the current generation of lead-free solders, new issues are forcing it to consider a change to lead-free solders that can be used at process temperatures even lower than those that were used with tin-lead solder.
One of those new issues is the unacceptably high incidence of defective joints caused by the warpage of BGA packages during the reflow profiles required by the current generation of lead-free solders. That warpage can result in complete separation of the solder during the reflow profile with no certainty that the parts attached to the pad and/or the component termination will remerge to form a low resistance connection when the package returns to its original shape during cooling. The result is defects such as “Head in Pillow” (HiP) and “Non-Wetted Opens” (NWO) that are difficult to detect by normal inspection methods and not easily repairable. With their increasingly complex structure, particularly if they incorporate heterogenous integration, it is proving impossible to build integrated circuit packages that, during the typical lead-free reflow profile, do not warp enough to cause these defects. The only solution offered by the manufacturers of these integrated circuit packages is to reduce the peak reflow temperature to no more than 200˚C. Another new issue driving the change to low process temperatures is the pressure on industry to reduce energy consumption in manufacturing processes to reduce the generation of greenhouse gases. It has been estimated that energy savings of more than a third can be achieved by reducing the peak temperature of reflow ovens from 250˚C to 190˚C. And a lower process temperature opens up opportunities for the use of cheaper materials for substrates and component packaging.
In the tin-bismuth system there is a eutectic at 58% bismuth with a melting point around 139˚C that has the potential for satisfying the requirement of a maximum reflow temperature of 200˚C. However, those alloys are far from a “drop-in” replacement for SAC305, SN100C or, for that matter, Sn-37Pb. Bismuth is a brittle metal and its presence in a low temperature solder tends to make it brittle.
In this presentation the author will review the factors driving the industry to low temperature processes and discuss solder alloy options and soldering processes.
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