In　order　to　investigate　subgrain　rotation　behavior　in　the　recrystallized　region　of　lead-free　solder　joints,　a　ball　grid　array　(BGA)　specimen　with　a　cross-sectioned　edge　row　was　thermally　shocked.　Electron　backscattered　diffraction　(EBSD)　was　used　to　obtain　the　microstructure　and　orientations　of　Sn　grains　or　subgrains　in　as-reflowed　and　thermally　shocked　conditions.　Orientation　imaging　microscopy　(OIM)　showed　that　several　subgrains　were　formed　at　the　tilted　twin　grain　boundaries,　near　the　chip　side　and　near　the　printed　circuit　board　(PCB)　side　after　200　thermal　shocks　due　to　a　highly　mismatched　coefficient　of　thermal　expansion　(CTE)　of　twin　grains.　Also,　subgrains　formed　at　the　chip　side　and　PCB　side　in　the　solder　joint　were　selected　to　research　the　grain　rotation　behavior　in　lead-free　solder　joints.　The　analysis　of　subgrain　rotation　also　indicated　that　the　rotation　behavior　of　subgrains　was　different　between　the　chip　side　and　PCB　side.　It　was　closely　related　with　the　large　different　crystal　orientations　between　the　chip　side　and　PCB　side.　Furthermore,　electron　backscattered　patterns　(EBSPs)　at　several　parts　of　the　joint　were　not　obtained　after　300　thermal　shocks　due　to　the　serious　deformation　caused　by　mismatched　CTE　during　thermal　shock.　But　4　subgrains　were　selected　and　compared　with　that　of　the　initial　state　and　200-thermal　shock　conditions.　The　results　showed　that　the　subgrains　at　the　chip　side　were　also　rotated　around　the　Sn　[101]　and　[001]　axes　and　the　subgrains　at　the　PCB　side　were　also　rotated　around　the　Sn　[100]　axis,　which　indicated　a　continuous　process　of　subgrain　rotation.