In　this　research,　a　composite　solder,　which　consisted　of　the　Sn-3.5Ag　eutectic　solder　matrix　and　Cu6Sn5　intermetallic　compounds　(IMCs)　as　reinforcements,　was　prepared　by　in　situ　method.　Cu　and　Sn　metallic　particles　were　added　into　the　molten　Sn-3.5Ag　eutectic　solder　to　form　Cu6Sn5　reinforcements　in　solder　matrix.　After　rolling,　the　Cu6Sn5　IMCs　are　crushed　into　fine　particles　and　distributed　uniformly　in　the　composite　solder.　The　creep　and　thermomechanical　fatigue　(TMF)　properties　of　the　Sn-3.5Ag　eutectic　solder　and　its　in　situ　Cu6Sn5　reinforced　composite　solder　joints　were　successively　investigated.　The　experimental　results　showed　that　the　in　situ　Cu6Sn5　reinforced　composite　solder　joint　exhibited　better　steady-state　creep　strain　rate,　lesser　TMF　damages　and　higher　residual　shear　strengths　after　different　number　of　TMF　cycles　as　compared　to　the　Sn-3.5Ag　eutectic　solder　joint.　These　indicated　that　the　in　situ　Cu6Sn5　reinforced　composite　solder　possessed　excellent　creep　resistance　and　TMF　properties.　Besides,　the　fracture　mode　of　the　in　situ　Cu6Sn5　reinforced　composite　solder　joint　and　the　role　of　the　in　situ　Cu6Sn5　reinforcing　particles　were　analyzed.　(C)　2010　Elsevier　B.V.　All　rights　reserved.