Effects of Aging on Interfacial Microstructure and Reliability Between SnAgCu Solder and FeNi/Cu UBM

Abstract

Abstract Effects of thermal aging on the interfacial microstructure and reliability of the SnAgCu/FeNi‐Cu joint are investigated. It is found that aging effects depends strongly on the temperature. Aging at low temperature, e.g., at 125 °C, a submicron meter thick FeSn 2 IMC layer formed at the SnAgCu/FeNi‐Cu interface during reflowing grows at a rate twenty times slower than the growth rate of the IMC at the SnAgCu/Cu interface. At high temperature, e.g., at 180 °C, the Cu element is found to diffuse through FeNi layer to produce the (Cu, Ni) 6 Sn 5 IMC and this IMC layer grows even faster than the IMC at the SnAgCu/Cu interface. Solder ball shear test results show that the SnAgCu/FeNi‐Cu joint has a comparable strength to the SnAgCu/Cu joint after reflowing, and the strength drop after aging at 125 °C is less than that of the SnAgCu/Cu joint. However, after aging at 180 °C, the strength of the SnAgCu/FeNi‐Cu joint is degraded to a low value, along with a shift in failure mode from the solder fracture to the brittle intermetallics fracture.