Morphology, evolution and performance of IMC in SAC105 solder/UBM (Ni (P)-Au)

To enhance the ability of lead-free solder joint to resist failures induced by mechanical impact and shock, some researchers have introduced low-Ag lead-free solder. In this study, the formation and evolution of IMC, the fracture morphology and performance of solder joint between SAC 105 solder and Under Bump Metallization (UBM) have been studied after different temperature storage aging and multi-reflow for WLCSP. The morphology and fracture surface of IMC have been analyzed by SEM, EDX and deeply etching techniques. The behavior of IMC and correlation with fracture mode of joint at high speed ball pull (HSBP) test has been investigated. It has been found that high temperature storage (HTS) aging results in IMC growing from one layer that is (Cu₆Sn₅) IMC to two different layers that are ((Cu,Ni)₆ Sn₅ and (Cu,Ni)₃Sn₄). Multi-reflow results in the IMC layer thickness increasing a little and some needle-like IMC grain spalling into the solder.