In　this　study,　Cu/Sn/Cu　structure　under　a　pressure　of　1.5　N　was　soldered　at　390-450　degrees　C.　Then,　microstructure　evolution　and　changes　in　mechanical　properties　of　solder　joint　during　the　formation　of　full　Cu41Sn11　joint　were　systematically　analyzed.　Experimental　results　showed　that　Cu6Sn5　and　Cu3Sn　were　observed　in　the　interfacial　region　at　420　C　in　the　early　stage　of　soldering.　The　Cu/Sn/Cu　structure　completely　transformed　into　Cu/Cu3Sn/　Cu　at　1　h.　With　the　further　progress　of　the　interfacial　reaction,　Cu41Sn11　appeared　and　grew　at　the　expense　of　Cu3Sn.　Eventually,　the　full　Cu41Sn11　joint　was　formed　at　10　h.　The　growth　of　Cu41Sn11　was　controlled　by　volume-diffusion.　Moreover,　diffusion　activation　energy　of　Cu41Sn11　was　about　108.19　kJ/mol.　The　shear　strength　of　full　Cu3Sn　joints　was　45　MPa,　while　that　of　the　solder　joints　with　25,　50,　75　and　100%　Cu41Sn11　was　50,　52.2,　59　and　64.5　MPa,　respectively.　For　full　Cu3Sn　and　full　Cu41Sn11　joints,　respectively,　the　fracture　occurred　partly　within　intermetallic　compounds　(IMCs)　layers　and　partly　along　the　Cu/IMC　interface.　However,　for　the　joints　composed　of　Cu3Sn　and　Cu41Sn11,　all　fractures　occurred　in　the　IMCs　layer.　Besides,　all　IMCs　joints　were　brittle　fracture,　and　the　fracture　of　Cu3Sn　was　mainly　intergranular,　while　the　fracture　that　occurred　in　Cu41Sn11　was　mainly　transgranular.