Effect of high temperature high humidity and thermal shock test on interfacial intermetallic compounds (IMCs) growth of low alpha solders

Abstract

In this study, the effects of high temperature high humidity aging conditions and thermal shock tests on the growth of intermetallic compounds (IMCs) in low alpha Sn–1.0Ag–0.5Cu (LA-SAC105) solder and low alpha Sn (LA-Sn) solder have been investigated. The aging has been performed at 50, 85 and 150 °C for 30, 70 and 120 h at a relative humidity (R.H.) of 40 and 85%. The thermal shock tests of LA solders has been performed from −65 to 150 °C for 100, 200, 400, 600, 800 and 1000 thermal cycles, and the results are compared with the normal SAC105 and Sn solders. It is observed that the evolution of Cu–Sn IMCs with aging time and temperature is diffusion controlled and the IMC thickness increases linearly with square root of aging time. The thickness of IMCs of LA-SAC105 and LA-Sn is smaller than that of SAC105 and Sn solders. It is also observed that as the number of thermal cycles increased, the IMC grain coarsening occurs in case of LA-SAC105 and as well as LA-Sn solders. In addition, whisker growth is noticed in LA-Sn and Sn solders. However, the LA-Sn has the lower sensitivity towards the whisker growth. On the contrary, a rapid growth and cracking of the IMCs formed at the interface of the normal SAC105/Cu system causes the solder sample to detach from the joint after 600 cycles, as compared to the LA-SAC105/Cu which resists the fracture up to 1000 cycles. The LA-SAC105 and LA-Sn can reduce the growth of IMCs when compared with the normal SAC105 and Sn as reference solders and may improve the solder joint reliability.