Investigation of the interfacial reactions and growth behavior of interfacial intermetallic compound between Sn37Pb solder and Au/Ni/Kovar substrate

Abstract

The interfacial reactions and microstructural evolution of Sn37Pb/Kovar with Au/Ni platings solder joints were investigated during isothermal aging at 120 °C, 150 °C and 170 °C for different duration, respectively. The experimental results indicated that a thin interfacial intermetallic compounds (IMCs) layer formed at the Sn37Pb/Kovar interface after reflowing process. The accurate compositions of thin IMCs were double-layers of (Ni, Au)3Sn4 and AuSn4, which were confirmed by utilizing TEM-EDS analysis. However, during the aging process, the compositions of interfacial IMCs of solder joint obviously changed, which transformed from AuSn4/(Ni, Au)3Sn4 to (Au, Ni)Sn4/Ni3Sn4 and the AuSn4 IMC formed in the bulk solder gradually changed to the (Au, Ni)Sn4 IMC. Furthermore, the total IMC thickness increased dramatically with increasing isothermal aging time, as well as aging temperature. The growth process of IMC layer is mainly dominated by the volume diffusion mechanism during the solid-state aging. The square of growth rate constant (K) equals to 2.559 × 10−17, 1.307 × 10−16 and 7.781 × 10−16 m2s−1 for the aging temperature of 120 °C, 150 °C and 170 °C, respectively. The activation energy (Q) value of the Sn37Pb/Kovar couple was calculated to be approximate 95.96 kJ·mol−1.