The　microcracking　behavior　of　the　IMC　layer　is　investigated　numerically,　and　the　effect　of　the　thickness　of　the　IMC　layer　on　the　overall　response　and　failure　mode　of　the　solder　joint　is　studied　using　qualitative　numerical　simulations.　The　results　show　that　the　thicker　IMC　layer　results　in　lower　overall　strength.　When　the　IMC　layer　is　thin,　the　microcracks　tend　to　start　at　the　valley　of　the　rough　solder/IMC　interface　and　propagate　across　the　root　of　the　protruding　Cu6Sn5　grains;　when　the　IMC　layer　is　thick,　the　microcracks　tend　to　occur　within　the　IMC　layer.　These　predictions　agree　well　with　experimental　observations.