Atomic　diffusion　in　soldering　process　leads　to　growth　and　stress　developed　in　the　intermetallic　compound　layer　in　solder　joints.　The　stress　and　morphological　evolution　of　the　intermetallic　compound　layer,　which　is　driven　by　the　stress,　result　in　degradation　of　mechanical　performance　of　solder　joints.　Microstructure　of　the　intermetallic　compound　layer　in　solder　joints　is　modeled.　The　model　consists　of　the　Cu6Sn5　layer.　The　Cu　atom　concentration　distribution　in　the　intermetallic　compound　layer　is　derived　based　on　the　Fick＇s　second　law.　Then　the　diffusion-induced　stress　is　obtained　analytically　by　transforming　atomic　diffusion　effects　into　bulk　strain.　The　results　show　that　the　diffusion-induced　stress　is　compressive.　When　the　diffusion　time　is　long　enough,　the　diffusion-induced　stress　has　a　linear　distribution　along　the　thickness　of　the　intermetallic　compound　layer.　©　2011　IEEE.