INTERFACIAL REACTIONS BETWEEN Sn-Ag-Cu LEAD-FREE SOLDERS AND IMMERSION SILVER SURFACE FINISH

In this study, interfacial reactions between Sn-Ag-Cu lead-free solder and immersion silver (ImAg) surface finish are investigated. The study also examines the effect of Cu and Sn contents in the Sn-Ag-Cu solders and solid state thermal aging on the type and morphology of intermetallic formed during soldering on immersion silver. Three different solder alloys were used which are SAC405, SAC305 and SAC3807 with one size of solder ball (700μm). The results revealed that after reflow soldering, Cu6Sn5 IMC is formed between solder and substrate while after aging treatment a new IMC was found between Cu6Sn5 IMC and substrate known as Cu3Sn. Aging of solder joints results in an increase of IMC’s thickness and changes their morphologies to become more spherical, dense and with larger grain size. The results show that the thickness of intermetallic formed is proportional to the aging duration. In terms of type of IMC in the bulk solder, both Ag3Sn plates and Cu6Sn5 rods were formed in the SAC405 and SAC3807 whereas only Cu6Sn5 rods were observed in the SAC305 solder.