The　ball　grid　array　(BGA)　component　with　cross-sectioned　edge　row　was　thermally　shocked　to　investigate　the　activated　slip　systems　in　the　Sn-3.0Ag-0.5Cu　lead-free　solder　joint.　The　microstructure　and　crystal　orientations　of　Sn-based　solder　joints　in　as-reflowed　and　thermally　shocked　conditions　were　obtained　by　scanning　electron　microscopy　(SEM)　and　electron　backscattered　diffraction　(EBSD),　respectively.　The　sample　was　reexamined　after　200,　300　and　400　thermal　shock　cycles　without　further　polishing.　In　this　paper,　one　single-crystal　solder　joint　in　a　BGA　component　was　selected　to　analyze　the　activated　slip　systems　during　recrystallization　under　the　thermally　shocked　cycled　condition.　Two　steps　were　used　to　determine　the　activated　slip　systems　in　this　study.　Step　one,　subgrain　rotation　angles　and　axes　were　calculated　by　the　Euler　angles　obtained　by　EBSD　before　and　after　thermal　shock.　Then　several　slip　systems　were　obtained　according　to　the　calculated　subgrain　rotation　axes.　Step　two,　in　order　to　further　determine　the　accurate　slip　system　which　could　cause　the　subgrain　rotation　along　the　axes　in　step　one,　the　theoretical　slip　traces　were　obtained　by　calculating　Euler　angles.　Because　the　results　contained　many　kinds　of　theoretical　slip　traces,　so　the　slip　bands　observed　by　SEM　were　used　and　assisted　to　select　the　theoretical　slip　traces.　Based　on　the　comprehensive　analysis　of　the　two　steps,　slip　systems　that　causes　the　serious　deformation　were　determined.　The　results　showed　that　recrystallization　occurred　at　different　areas　of　the　solder　joint　and　the　slip　bands　appeared　at　the　corners　of　the　solder　joint.　The　subgrain　rotation　behavior　was　variable　at　the　recrystallization　area　by　analyzing　the　subgrain　orientation　after　200,　300　and　400　thermal　shock　cycles.　By　compared　the　as-calculated　slip　traces　with　the　slip　bands　characterized　by　SEM　and　the　rotation　axes　calculated　by　the　Euler　angles,　(0　0)　[0　0　1],　(1　0)　[0　0　1]　and　(1　1　0)　[0　0　]　were　the　slip　systems　that　caused　the　subgrain　rotation　along　a　certain　axis　in　this　solder　joint.