Improving　the　reliability　of　solder　joints　is　an　urgent　issue　to　guarantee　the　quality　of　surface　assembly　products.　The　size　of　components　and　pitches　on　the　circuit　board　differs　from　each　other　which　leads　to　the　size　of　solder　joints　variation　one　by　one.　In　this　study,　the　size　effect　of　solder　powder　on　Sn-3.0Ag-0.5Cu　solder　joints　in　high　density　LED　display　packaging　was　investigated.　The　microstructure　and　shear　stress　of　the　solder　joints　were　observed　as-reflowed　and　after　different　thermal　cycling　period　conditions.　The　study　suggested　that　the　type　3　solder　joint　had　good　reliability　and　mechanical　property　than　others.　So　the　type　3　Sn-3.0Ag-0.5Cu　solder　powder　was　recommended　the　best　to　package　this　high　density　LED　display.　©　2012　IEEE.