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, CuR6RSnR5R IMC is formed between solder and substrate while after aging treatment a new IMC was found between CuR6RSnR5R IMC and substrate known as CuR3RSn. 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 AgR3RSn plates and CuR6RSnR5R rods were formed in the SAC405 and SAC3807 whereas only CuR6RSnR5R rods were observed in the SAC305 solder.

Keywords:

Lead-free , solder , immersion silver , intermetallic compound , aging , surface finish