White　light-emitting　diodes　(LED)　are　widely　applied　in　many　fields　for　its　special　advantages　compared　with　other　light　sources.　Chip-scale-package　(CSP)　is　one　of　the　hotspots　in　the　research　of　microelectronics,　and　also　the　main　stream　and　development　direction　to　the　future　package　technology.　Within　a　CSP,　the　solder　layer　between　LED　chip　and　substrate　is　usually　achieved　via　reflow　processes.　The　weldability　of　solder　layer　with　substrate　directly　determines　CSP＇s　reliability　and　service　life.　Therefore,　optimizing　reflow　soldering　process　can　improve　the　performance　of　solder　layer,　and　improve　the　reliability　of　CSPs.　The　Sn-3.0Ag-0.5Cu　(SAC305)　has　been　widely　used　in　high　power　LED　CSPs　for　its　good　solderability　and　favorable　shear　strength.　In　this　paper,　the　reflow　soldering　process　for　SAC305　is　optimized,　by　considering　the　reflow　profile,　the　volume　of　solder　paste　and　the　substrate　materials,　to　improve　the　bonding　strength　between　solder　layer　and　substrate.　Then　the　shear　tests　and　simulation　results　are　used　to　verify　the　mechanical　performance　of　CSP　solder　layer.　Finally,　an　optimized　reflow　process　is　proposed　for　white　LED　CSP　packaging.　The　results　show　that　the　reflow　temperature　curve　should　be　in　an　appropriate　level,　and　the　performance　of　the　ceramic　substrate　is　more　suitable　for　the　SAC305　solder　paste　than　the　aluminum　substrate.