Study on Inter-Metallic Compound (IMC) at Interface of Pb-Free Solder and Nickel UBM for Mobile Application

This study is confirmed and provided a reliable solder joint reliability about Ni UBM/penetration layer/SnAg lead-free solder bump structure for mobile application. Investigated of the mechanical strength and evaluated with ball shear test the Ni UBM/penetration layer/SnAg lead-free solder bump structure after 10 times multi reflow test, isothermal aging at 150degC for 1000 hours and thermal cycling test at -55degC~125degC for 1000 cycles. After comparing ball shear test with the Cu UBM/SnAg lead-free solder bump structure and the Ni UBM/penetration layer/SnAg lead-free solder bump structure, it was observed UBM (under bump metallurgy) consumption and IMC thickness. Then, there have confirmed the composition of IMC(inter-metallic compound) in the Ni UBM/penetration layer/SnAg lead-free solder bump structure and Cu UBM/SnAg lead-free solder bump structure and the formation ternary IMC of (Cu, Ni)₆Sn₅ and binary IMC of Cu₆Sn₅, respectively. The result of ball shear fracture mode was occurred in solder bump and did not show shear strength degrade. According to 10 times multi reflow, thermal cycling test at -55degC~125degC and high temperature storage (HTS, isothermal aging) at 150degC using ball shear test, that confirmed good mechanical strength and a reliable solder joint reliability of the Ni UBM/penetrate layer/SnAg lead-free solder bump structure so have to good mechanical strength that provided a reliable solder joint reliability.