Phase field simulations of morphological evolution and growth kinetics of solder reaction products

Two-dimensional simulations of the morphological and growth evolutions of the intermetallic compound (IMC) formed between a Sn-based solder and a Cu pad are performed using a multiphase field model, in order to examine the difference between the IMC growth behavior for the soldering reaction and that for the solid-state aging after soldering. The simulations show that the scallop-type IMC morphology formed in the soldering reaction is governed not only by the surface energy difference between the solder/IMC interface and the IMC grain boundary (GB), but also by the difference in diffusivities in the liquid solder and the IMC GB. It is also shown that the orders of magnitude difference in the IMC growth rate between the soldering reaction and the subsequent aging process is mainly attributed to the increased IMC GB distance resulting from the morphological change of the IMC from a scallop type to a layer type. The change in the solder diffusivity itself, however, has only a minor influence on the IMC growth kinetics of the layer-type IMC in the subsequent aging process.