Phase-field simulations of intermetallic compound growth in Cu/Sn/Cu sandwich structure under transient liquid phase bonding conditions

The microstructural evolution of eta(Cu6Sn5) and epsilon(Cu3Sn) in a Cu/Sn/Cu structure under transient liquid phase bonding conditions is numerically investigated through the use of the multiphase-field method. The material parameters and reaction conditions were adopted from relevant experimental research. Simulation results were then analyzed and compared with the experiments in terms of morphology of intermetallic compound (IMC) grains, growth ratio of the eta layer with respect to the a layer, evolution of each layer and roughness of each interface. Additionally, it is shown through the use of simulation data that, while liquid Sn is present, the growth of the eta IMC layers is dominant and that, upon the exhaustion of liquid Sn, the eta grains of the upper and lower layers impinge on one another, at which time the larger grains continue to coarsen at the expense of the smaller grains. Concurrently, the growth of the epsilon layers becomes significant and continues to increase until the eta layer is fully consumed or the reaction is thermally arrested. Overall, the simulations were found to be in good qualitative agreement with experiments for morphology of the IMC grains, while showing good quantitative agreement, in spatial extent and elapsed time frames, for the evolution of each of the IMC layers and the derived growth ratio of the eta layer with respect to the epsilon layer. Furthermore, it is shown that the results corresponding to different thickness values for the initial Sn layer suggest that the IMC evolution can be reasonably predicted in advance of experimental studies. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.