Kinetics of interface reaction in 40Sn-Bi/Cu and 40Sn-Bi-2Ag/Cu systems during aging in solid state

Abstract

The characteristics of thickening kinetics of the intermetallic compounds (IMC) (Cu 6 Sn 5 + Cu 3 Sn) during aging at 120 C and 90 C in solid state were studied by quantitative metallographic analysis for three solder alloy systems: 40Sn-Bi/Cu, 40Sn-Bi-2Ag/Cu and Sn-37Pb/Cu. The diffusion couple were prepared by hot immersion in the molten solder bath. The results showed that the rate of the IMC thickening increases in the order Sn-37Pb/Cu 40Sn-Bi/2Ag/Cu 40Sn-Bi/Cu. The IMC thickening rate in the Sn-Bi eutectic system is one order of magnitude faster than that in Sn-Pb eutectic system. The time exponents are different from each other. The relationship between the increase of IMC and aging time follows a parabolic function in Sn-Pb system, and a linear relation in Sn-Bi system. Addition of Ag in Sn-Bi inhibits the IMC thickening process.