With　packaging　density　constantly　increasing　and　the　size　of　solder　joints　scaling　down　in　microelectronic　products,　electromigration　(EM)　becomes　serious　reliability　problem　in　interconnections　which　induced　by　the　high　current　density.　Currently,　investigations　on　EM　phenomenon　mainly　focus　on　microstructure　evolution,　the　change　of　grain　orientation　and　the　dominant　diffusion　species,　etc.　Almost　all　these　studies　and　EM　damages　are　carried　out　under　constant　ambient　temperature.　However,　electronic　devices　usually　service　in　a　non-equilibrium　state　environment　in　practical.　The　purpose　of　this　research　is　investigating　the　EM　behavior　under　the　thermal　cycling　conditions　and　trying　to　understand　the　relationship　between　microstructure　evolution　and　resistance　change　of　the　solder　joints.　The　one-dimensional　Cu/Sn3.0Ag0.5Cu/Cu　linear　solder　joint　was　employed　to　study　the　EM　behavior　of　Sn-3.0Ag-0.5Cu　(SAC305)　under　combined　conditions　of　cycling　temperature　ranges　from　-20　to　100　°C　and　a　high　current　density　of　104A/cm2.　Resistance　change　and　microstructure　evolution　were　analyzed　in　this　paper.　Resistance　and　microstructure　data　was　collected　and　observed　by　paperless　recorder　and　scanning　electron　microscope　(SEM),　respectively.　The　results　revealed　that　high　current　density　can　cause　voids　formation.　The　propagation　of　cracks　was　accelerated　by　cycling　temperature　due　to　the　mismatch　of　coefficient　of　thermal　(CTE)　between　solder　matrix　and　Cu　substrate.　Moreover,　the　coupling　effects　of　high　density　and　cycling　temperature　can　lead　to　a　rapid　failure　when　compare　to　the　monolithic　loading　condition.　©　2012　IEEE.