The　composite　approach,　by　incorporating　small　amounts　of　reinforcement　particles　in　the　solder　matrix,　has　proven　to　be　one　of　the　effective　ways　to　improve　the　reliability　of　solder　joints.　The　effects　of　Cu　addition　on　electromigration　were　investigated　in　this　study　by　incorporating　2%　volume　fraction　Cu　particles　into　Sn-3.5Ag　eutectic　solder　paste　by　the　in　situ　process.　The　one-dimensional　solder　joints,　designed　to　prevent　the　current　crowding　effect,　were　stressed　under　a　constant　current　density　of　10(4)　A/cm(2)　at　room　temperature,　and　the　temperature　of　the　sample　could　reach　105　+/-　5A　degrees　C　due　to　the　Joule　heating　effect.　Doping　2　vol.%　Cu　was　found　to　retard　the　electromigration　phenomenon　effectively.　After　electric　current　stressing　for　528　h,　the　growth　rate　of　an　interfacial　intermetallic　compound　(IMC)　layer　at　the　anode　decreased　73%　in　contrast　to　that　of　Sn-3.5Ag　solder　joints,　and　the　IMC　layer　at　the　cathode　was　almost　unchanged.　The　polarization　effect　of　Cu　reinforced　composite　solder　joints　was　also　apparently　mitigated.　In　addition,　the　surface　damage　of　the　composite　solder　joints　was　relieved　by　incorporating　2　vol.%　Cu　particles.　Compared　to　Sn-3.5Ag　solder　joints,　which　had　protruded　Cu6Sn5　and　wrinkles　of　Sn-solder　matrix　on　the　surface,　the　solder　joints　with　Cu　addition　had　a　more　even　surface.