The　failure　mode　and　mechanism　of　BGA　packages　were　explored　by　drop　tests　of　PCB　packages.　Furthermore,　the　initiation　mechanism　and　expanding　features　of　cracks　were　analyzed　in　this　work.　Results　showed　that,　cracks　in　the　solder　joints　and　structural　fractures　of　PCB　are　the　main　reasons　that　cause　the　failure　of　BGA　packages.　There　are　two　main　kinds　of　cracks　in　solder　joints　which　distribute　on　the　joint　top　and　bottom,　and　the　initiation　mechanism　of　them　are　different.　Micro　gaps　between　the　solder　joint　and　solder　resist　film　that　caused　by　gravity　contribute　to　the　cracks　on　the　top.　Cracks　on　the　bottom　are　caused　by　the　gaps　on　both　sides　of　the　remained　solder　flux　that　existed　between　the　solder　joint　and　the　solder　resist　film　under　drop-impact　load.　The　expanding　of　cracks　has　a　relationship　with　the　original　location,　orientation　and　stress　conditions　of　the　crack　sources.　Relative　position　of　solder　joint　and　pad　also　have　important　influence　on　the　expanding　of　cracks.　©　2016,　Editorial　Board　of　Transactions　of　the　China　Welding　Institution,　Magazine　Agency　Welding.　All　right　reserved.