SMT007 Magazine

SMT-Aug2016

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92 SMT Magazine • August 2016 ered a real problem. However, today the same joints are considered a problem, but this might only be because we now have the ability to ob- serve them under high resolution x-ray inspec- tion! Poul Juul (manager of Hytek, Denmark) presented an interesting review relating vari- ous types of voids in solder joints to reliability concerns. He discussed the root causes of dif- ferent kinds of voids and concluded that voids in solder fillets could be reduced by optimizing the quality of surface finishes on components and PCB pads. The selection of correct solder alloy and flux is also important, as is the opti- mization of soldering temperatures and profiles. Luca Moliterni (IIS Progress, Italy) compared the impact of "automated paste in hole solder- ing" with "automated selective wave soldering" on the reliability of electronic assemblies. He described the characteristics of both soldering technologies. A chart compared "paste in hole" and "selective wave" against important param- eters that included energy consumption, flux contamination, repeatability, defects (solder and short circuits), component availability and the prospect of successful industrialization of these processes. The final presentation was made by Martin Wickham (National Physics Laboratory, UK). Martin assessed various sintered materials and conductive adhesives as alternatives to high temperature solder alloys. Such high temperature at- tachment processes are required for electronics incorporated within high performance power equip- ment, electrical vehicles and spacecraft such as the current ESA BepiColom- bo mission (to the planet Mercury) where electri- cal systems are expected to endure temperatures in access of 350°C. High lead- containing alloys are no longer permitted by RoHS legislation. Electrical con- nections between various ceramic component termi- nations and PCB finishes have been evaluated by NPL using conductive adhesive such as Elcosint. The properties of conductive adhesives were compared against samples made using conventional high melt- ing point solder alloys. Preliminary test results, based on thermal ageing and thermal cycling, were presented and results demonstrated the Elcosint® materials (Figure 8) to have outper- formed each solder alloy. Additional work is planned and will be supported by the sponsor- ing partners—persons interested in joining this partnership can contact Martin at NPL. EMPS workshops are publicized on a Uni- versity of Portsmouth website from which all past presentations (2010–2016) can be freely downloaded. For those wishing to present their work or attend the next Workshop, EMPS-8 will be hosted by ESA-Estec, in Noordwijk, the Netherlands on 10–12 April, 2017. Details will be announced here. SMT Barrie Dunn is an EMPS (Electronic Materials and Processes for Space) co-founder, and professor at the University of Portsmouth. Previously, he was with the European Space Agency as head of materials and processes division. 7TH ELECTRONIC MATERIALS AND PROCESSES FOR SPACE WORKSHOP Figure 8: Micrograph of a high temperature adhesive under evaluation at the National Physics Laboratory, UK.

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