The　crack　growth　in　solder　joint　of　SMT　during　thermal　fatigue　process　is　investigated　by　experimental　method.　Two　kinds　of　land　shapes　and　two　kinds　of　solders,　including　lead-tin　eutectic　solder　and　lead-free　solder　(SAC305),　are　selected.　In　order　to　investigate　the　crack　growth　in　solder　joint,　the　solder　joint　is　sliced　and　the　crack　on　the　cross　section　of　solder　joint　is　observed.　Some　conclusions　are　drawn:　During　thermal　fatigue　process　the　solder　joint　experiences　two　stages　of　crack　growth,　including　crack　initiation　and　crack　propagation,　in　which　the　period　of　crack　initiation　is　shorter.　In　the　late　period　of　thermal　fatigue,　crack　goes　through　the　solder　joint,　to　fail.　And　there　are　two　kinds　of　crack　growth　modes　observed　in　the　experiment.　The　crack　growth　mode　of　lead-free　solder　joint　is　obviously　different　from　that　of　lead-tin　solder　joint.　Experimental　results　also　show　that　the　solder　joint　with　small　land　shape　has　a　relatively　poor　thermal　fatigue　resistance　and　the　lead-free　solder　joint　of　SAC305has　a　thermal　fatigue　resistance　better　than　that　of　lead-tin　solder　joint.　©　2010　Journal　of　Mechanical　Engineering.