Lead-free solder evaluation for ball attache process

In recent years, increasing awareness of lead-free requirement in electronics industry is driving the need to investigate lead-free solder systems in detail. This paper investigates three types of solder alloys, Sn/3.8Ag/0.7Cu, Sn/3.5Ag and Sn/0.7Cu used in a ball attache process. The scope of this paper covers lead-free solder system, comprehensively from ball attache process to board assembly reliability. This includes study on intermetallics at substrate-ball interface, PCB-ball interface, solid state diffusion study, shear force trend, failure modes and thermal cycling study of solder joints when assembled with Ni/Au and OSP finished PCBs. It was observed that the low processing temperature of Sn/3.5Ag and Sn/3.8Ag/0.7Cu make them viable lead-free alloys to implement in assembly lines. The solder life performance of these alloys is better than Sn/37Pb alloy on Ni/Au PCB but does not fare well on OSP finished PCBs. On the other hand, Sn/0.7Cu solder has a process temperature that is ten degrees above Sn/3.5Ag and Sn/3.8Ag/0.7Cu but solder life performance on Ni/Au and OSP finished PCBs fares better than other lead-free and tin-lead alloys.