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32 SMT007 MAGAZINE I JULY 2021 Feature Article by Ranjit Pandher MACDERMID ALPHA ELECTRONICS SOLUTIONS e drop shock reliability of solder joints has become a major issue for the electronic industry not only because of the ever-increas- ing popularity of portable electronics and the widespread use of lead-free solders, but also in ensuring high first-pass yield during han- dling in a production environment. Most of the commonly recommended lead-free solders are high tin (Sn) alloys which play a critical role in reliability of lead-free solder joints as high Sn alloys have relatively higher strength and mod- ulus. Further, even though metallurgically, it is the Sn in the solder alloys that principally par- ticipates in the solder joint formation, details of the intermetallic compound (IMC) layers formed with tin-lead (SnPb) and Pb-free alloys are different. e markedly different process conditions for SnPb and Pb-free alloys also bear on solder joint quality. Brittle failure of solder joints in drop shock occurs at or in the interfacial IMC layer(s). is is due to the inherent brittle nature of the IMC, defects within or at IMC interfaces, or transfer of stress to the interfaces as a result of the low ductility of the bulk solder. In developing improved performance alloys, MacDermid Alpha has addressed both issues— improved ductility, and modification and con- trol of the intermetallic layer. A broad range of base alloy compositions together with selected micro-alloying additions to SnAgCu alloys have been evaluated with the objective of con- trolling bulk alloy mechanical properties and the diffusion processes operating in the forma- tion and growth of the intermetallic interfacial layer(s). e alloy additives generally act as diffusion modifiers slowing interdiffusion rate between substrates and solder thereby reducing IMC thickness or the propensity for void forma- tion. Alternatively, additions can be made that act as diffusion compensators. It should be noted that the level of the micro-additions does not measurably modify the bulk mechan- ical properties of the base alloys. Our results show that dramatic improvements in the sol- der joint reliability, as demonstrated by high- Ductility is Your Greatest 'Alloy:' Avoiding Drop Shock Failures

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