Effects of Cu orientation and stand-off-height on the microstructure of Cu/SnAgCu interface

Abstract

The effects of Cu orientation and stand-offheight on the microstructure and growth of IMCs in Cu/S nAgCu/Cu solder joints was investigated. Cu 6 Sn 5 and Cu 3 S n were the two key intermetallic compounds (IMCs) that formed at the interface. On (111) Cu substrate, prism-like Cu 6 Sn 5 grains could be observed after reflowing at 250 for 10s. On polycrystalline Cu substrate, only scallop-like Cu 6 Sn 5 grains formed and the grain size is smaller than that of (111) Cu. Then, samples were aged at 150 and the thickness of Cu 6 Sn 5 and Cu 3 Sn layers increased with the increasing aging time. We found that Cu 3 S n formed on (111) Cu substrate grew faster than that on polycrystalline Cu substrate , owing to Cu 3 S n columnar growth on (111) Cu and grain boundary diffusion control. After aging at 150 for 384 h, the IMC growing from the upper side and from the lower side touched each other in solder joints with 10 m SOH. Cu 6 Sn 5 stopped growing while Cu 3 Sn continued growing at the consumption of Cu 6 Sn 5 , resulting in the decrease of thickness of Cu 6 Sn 5 .