Thermomechanical　fatigue　of　SnAgCu/Cu　solder　joints　subjected　to　thermal　cycling　was　investigated.　Based　upon　an　analysis　of　displacements　for　flip-chip　solder　joints　subjected　to　temperature　cycling,　a　special　bimetallic　loading　frame　with　single　solder　joints　has　been　designed,　which　allows　for　the　strain　measurements　of　an　individual　solder　joint　during　thermal　cycling.　The　strain-stress　relationship　for　the　solder　joint,　characterized　by　hysteresis　loops,　was　determined　by　strain　gauge　measurement　during　thermal　cycling　from　-40　to　125　degrees　C.　The　failure　process　was　characterized　by　resistance　change　of　the　solder　joints,　and　the　number　of　cycles　to　failure　was　determined　when　the　variable　D=1-R-0/R　approximately　reached　0.5.　The　results　show　that　the　failure　process　of　solder　joints　is　accelerated　with　the　increase　of　strain　range　applied.　Coffin-Masson　law　was　applied　to　characterize　the　relationship　between　solder　joint　life　and　inelastic　strain　range,　and　the　model　parameters　were　determined　for　SnAgCu/Cu　solder　joint.　In　addition,　the　microstructure　evolution　of　the　solder　joints　during　thermal　cycling　was　analyzed　by　Scanning　Electron　Microscopy,　which　gave　the　microscopic　explanation　for　the　failure　mechanism　of　SnAgCu/Cu　solder　joints.