Interfacial structure and growth kinetics of intermetallic compounds between Sn-3.5Ag solder and Al substrate during solder process

Interfacial reactions between liquid-state Sn-3.5Ag solders and solid-state Al substrates were investigated in this study. The microstructure and growth kinetics of intermetallic compound (IMC) were studied at temperature from 250 °C to 285 °C for 60 min. A layer of Ag2Al IMC was detected forming at the interface and a mass of grains with deep gaps were also observed in the IMC layers. The calculated results of growth kinetics indicated that the growth evolution involves chemical reaction-limited stage (the time exponent n = 1) and the grain boundary diffusion-controlled stage (n = 0.33). When the temperature was elevated from 250 °C to 285 °C, the critical time of transition for the two stages reduced and the corresponding critical thickness increased. The activation energy Q obtained in the chemical reaction-limited stage and the diffusion-controlled stage is 84.105 ± 2.571 kJ/mol and 26.385 ± 3.171 kJ/mol, respectively.