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

The effects of Cu orientation and stand-off-height on the microstructure and growth of IMCs in Cu/SnAgCu/Cu solder joints was investigated. Cu₆Sn5 and Cu₃Sn were the two key intermetallic compounds (IMCs) that formed at the interface. On (111) Cu substrate, prism-like Cu6Sn5 grains could be observed after reflowing at 250°C for 10s. On polycrystalline Cu substrate, only scallop-like Cu6Sn5 grains formed and the grain size is smaller than that of (111) Cu. Then, samples were aged at 150°C and the thickness of Cu6Sn5 and Cu3Sn layers increased with the increasing aging time. We found that Cu3Sn formed on (111) Cu substrate grew faster than that on polycrystalline Cu substrate, owing to Cu3Sn columnar growth on (111) Cu and grain boundary diffusion control. After aging at 150°C for 384 h, the IMC growing from the upper side and from the lower side touched each other in solder joints with 10 um SOH. Cu₆Sn5 stopped growing while Cu3Sn continued growing at the consumption of Cu₆Sn₅, resulting in the decrease of thickness of Cu₆Sn₅.