Because　of　its　tetragonal　structure,　beta-Sn　exhibits　anisotropy　in　electromigration　behavior.　The　diffusivity　of　Cu　atoms　along　the　c-axis　of　Sn　is　much　faster　than　that　along　the　a-axis;　therefore,　the　orientation　of　the　c-axis　exerts　a　strong　influence　on　Cu　atomic　motion.　In　this　work,　the　effect　of　Sn　grain　c-axis　on　Cu　atomic　motion　was　investigated　by　using　Cu　reinforced　Sn3.5Ag　composite　solder　joints.　The　microstructure　and　morphology　of　the　solder　joints　were　characterized　by　scanning　electron　microscopy　(SEM)　equipped　with　a　backscattered　electron　(BSE)　detector.　It　was　found　that　intermetallic　compounds　(IMCs)　in　the　solder　matrix　were　formed　due　to　the　migration　of　Cu　atoms　to　the　surface　of　the　solder　joint　under　current　stressing.　There　was　a　large　amount　of　IMCs　on　the　solder　matrix　which　protruded　from　the　solder　matrix.　By　changing　the　direction　of　electron　flow,　i.e.　changing　the　anode　and　the　cathode　side,　the　IMCs　which　formed　after　current　stressing　in　the　solder　matrix　disappeared　and　the　protruding　Sn　remained　unchanged.　The　results　revealed　that　the　growth　of　IMCs　was　closely　related　to　the　migration　of　Cu　atoms,　while　Cu　atomic　motion　depended　on　the　orientation　of　the　Sn　grain　c-axis.