This　study　quantitatively　characterized　the　grain　orientation　evolution　of　Sn3.0Ag0.5Cu　ball　grid　array　(BGA)　solder　joints　subjected　to　thermomechanical　stress　using　electron　backscatter　diffraction　(EBSD).　Further　polishing　of　the　as-reflowed　solder　joint　cross　sections　was　avoided　after　thermal　shock　treatment　to　accurately　analyze　the　underlying　mechanism　of　recrystallization.　No　previous　reports　have　been　presented　on　this　topic　because　of　the　inability　to　conduct　pattern　indexing　due　to　crosssectional　contamination　after　thermomechanical　fatigue.　The　results　show　that　the　pre-existing　low-angle　boundaries　in　the　as-reflowed　joints　tend　to　gradually　increase　in　misorientation　and　that　low-angle　boundaries　inhomogeneously　increase　mainly　by　the　cross-slip　and　climb　of　dislocations.　Recovery　tends　to　occur　at　the　pre-existing　low-angle　boundaries　in　the　as-reflowed　joints　and　the　regions　in　the　solder　joints　near　the　package　interface　composed　of　a　single　grain,　and　there　is　a　partial　release　of　stored　energy　prior　to　recrystallization.　However,　the　residual　stored　energy　remains　sufficiently　high　to　induce　subsequent　recrystallization　in　the　deformed　solder　alloy　after　subgrain　formation.　The　transition　process　from　subgrains　to　recrystallized　grains　is　continuous,　and　subgrains　appear　before　the　formation　of　recrystallized　grains　in　the　Pb-free　solder　joints　subjected　to　thermomechanical　stress.　The　orientations　of　the　small　recrystallized　grains　separated　by　the　low　angle　boundaries　evolve　from　the　initial　orientations　by　subgrain　rotation.　Additionally,　the　subgrain　rotation　behavior　of　Pb-free　solder　joints　was　investigated　in　terms　of　the　rotation　axis　and　angle.　The　results　show　that　there　is　typically　a　single　rotation　axis　for　each　subgrain　in　the　early　stages　of　recrystallization.　This　finding　confirms　the　interrelationship　between　the　activated　beta-Sn　slip　systems　and　the　process　of　recrystallization　in　Pb-free　solder　joints.　(C)　2017　Elsevier　B.V.　All　rights　reserved.