The　requirements　for　lead-free　electronics　lead　to　the　development　of　new　Pb-free　solders.　The　Sn-3.0-Ag-0.5Cu　(SAC305)　is　one　of　them　and　is　widely　used　in　the　lead-free　solder　market.　But　the　melting　point　of　it,　217°C,　exceeds　that　of　traditional　Sn-37Pb　solder.　The　lower　melting　temperature　of　lead-free　solder　are　needed　to　meet　the　requirements　of　the　manufacturing　process　that　depend　on　conventional　Sn-Pb　based　reflow　equipment.　Adding　Bi　can　reducing　the　melting　point,　but　it　will　affect　the　mechanical　properties.　Adding　In　can　also　reduce　the　melting　point　without　reducing　the　mechanical　strength　of　the　joints.　But　In　is　rare　and　expensive.　Therefore,　there　are　Sn-Ag-Bi-In　solders,　four　alloy　solder　systems,　by　adding　the　two　kinds　of　elements　into　Sn-Ag　based　solder.　Sn-3Ag-3Bi-3In　(SABI333)　is　an　alternative　four　alloy　Pb-lead　solder,　with　a　melting　temperature,　198°C,　close　to　that　of　eutectic　Sn-Pb　solder.　This　study　elucidates　the　microstructure　and　intermetallic　compounds　(IMCs)　formed　at　the　interfaces　and　in　the　bulk　solder　in　SABI333　solder　joints　on　Cu　matrix.　In　the　reactions　between　Sn-Bi-In　solders　and　Cu　matrix,　the　compounds　formed　at　the　interfaces　were　Cu6　(Sn,　In)5.　Whereas,　in　SABI333　solder　joint,　the　compounds　formed　at　the　interfaces　were　Cu6Sn5　and　Cu3Sn,　without　the　substitution　of　Sn　by　In.　The　compound　formed　in　the　bulk　solder　was　identified　as　Cu6Sn5,　which　is　totally　different　from　the　SAC305　and　Sn-Bi-In　solders.　The　quantitative　test　of　exact　compound　composition　of　IMC　formed　at　the　interface　and　in　the　bulk　solder　joints　was　determined　by　electron　microprobe　analysis　(EPMA).　©　2017　IEEE.