The interfacial reaction between In-48Sn solder and polycrystalline Cu substrate during solid state aging

Abstract

Intermetallic compounds (IMCs) with three different morphologies were formed through an interfacial reaction between In-48Sn solder and polycrystalline Cu substrate, which are chunk-type Cu(In,Sn)2 and duplex structural Cu2(In,Sn). Two types of phase transformations between Cu(In,Sn)2 and Cu2(In,Sn) IMCs occurred during low temperature aging (20 °C and 40 °C) and high temperature aging (60 °C, 80 °C and 100 °C), respectively. At lower aging temperature, the duplex structural coarse-grain and fine-grain Cu2(In,Sn) transformed into Cu(In,Sn)2, and a characteristic evolution model was provided. At a higher aging temperature, Cu(In,Sn)2 transformed completely into Cu2(In,Sn) within a very short time period. Based on the designed Cr-marker experiments, the growth kinetics of coarse-grain and fine-grain Cu2(In,Sn) sublayers at higher aging temperatures were investigated. It was concluded that the growth mechanism of Cu2(In,Sn) is temperature dependent, which is volume-diffusion-controlled at 60 °C–80 °C, whereas grain boundary diffusion becomes rate-controlling at 100 °C. Through an elaborate design of aging test at 80 °C and 20 °C alternately, the reversible transformation between Cu2(In,Sn) and Cu(In,Sn)2 was observed and characterised.