Sn-Pb　alloys　have　widely　been　used　in　industry　for　many　years.　However,　in　the　European　Union,　the　use　of　Pb　in　electronics　was　prohibited　from　1　January　2008　because　Sn-Pb　alloys　cause　serious　pollution　to　environment.　Therefore,　the　interfacial　reactions　between　lead-free　solders　(Sn-Ag,　Sn-Ag-Cu　and　Sn-Cu)　and　substrates　as　well　as　their　mechanical　properties　have　attracted　much　attention　from　many　researchers.　The　Cu/Sn-based　solder/Cu　system　has　been　broadly　used　in　high-density　integrated　circuits　such　as　three-dimensional　(3D)　integration.　With　increasing　density　in　device　integration,　the　size　of　the　solder　joints　will　continue　to　decrease.　As　a　result,　the　joints　are　composed　of　a　limited　number　of　solders　and　intermetallic　compounds　(IMCs)　grains.　Moreover,　the　proportion　of　IMCs　in　the　joints　has　also　increased.　Therefore,　the　microstructure　of　solder　joints　has　great　influence　on　the　reliability　of　solder　joints,　and　the　IMC　is　always　a　great　core　of　solder　joints　microstructure.　Different　morphology　of　IMCs　will　greatly　affect　the　properties　and　reliability　of　solder　joints,　but　the　mechanism　of　this　growth　behavior　and　its　impact　on　the　reliability　of　solder　joints　is　not　clear.　The　purpose　of　this　research　is　to　investigate　the　growth　behavior　of　prism-type　Cu6Sn5　in　the　liquid　solder.　The　sample　in　the　experiment　was　made　from　the　mixture　of　the　Sn3.5Ag　solder　paste　and　2　vol.%　Cu　particles　and　blended　for　30　min　to　ensure　homogeneous　distribution　of　Cu　particles.　The　experimental　sample　was　insulation　in　an　aging　oven　at　240　°C　for　60s　and　cooled　in　air.　Then　the　samples　were　analyzed　by　Scanning　Electron　Microscope　(SEM).　The　results　showed　that　the　Cu　of　prism-type　Cu6Sn5　can　come　from　the　solder.　The　edge　of　the　solder　ball　cooling　fast,　high　temperature　phase　η-Cu6Sn5　was　retained.　©　2017　IEEE.