A　design　of　experiment　(DOE)　methodology　based　on　numerical　simulation　is　presented　to　improve　thermal　fatigue　reliability　of　multirow　quad　flat　nonlead　(QFN)　packages.　In　this　method,　the　influences　of　material　properties,　structural　geometries,　and　temperature　cycling　profiles　on　thermal　fatigue　reliability　are　evaluated,　a　L-27(3(8))　orthogonal　array　is　built　based　on　Taguchi　method　to　figure　out　optimized　factor　combination　design　for　promoting　thermal　fatigue　reliability.　Analysis　of　variance　(ANOVA)　is　carried　out　to　examine　the　influence　of　factors　on　the　thermal　fatigue　reliability　and　to　find　the　significant　factors.　Anand　constitutive　model　is　adopted　to　describe　the　viscoplastic　behavior　of　lead-free　solder　Sn3.0Ag0.5Cu.　The　stress　and　strain　in　solder　joints　under　temperature　cycling　are　studied　by　3D　finite　element　(FE)　model.　The　modified　Coffin-Manson　model　is　employed　to　predict　the　fatigue　life　of　solder　joints.　Results　indicate　that　the　coefficients　of　thermal　expansion　(CTE)　of　printed　circuit　board　(PCB),　the　height　of　solder　joint,　and　CTE　of　epoxy　molding　compound　(EMC)　have　critical　influence　on　thermal　fatigue　life　of　solder　joints.　The　fatigue　life　of　multirow　QFN　package　with　original　design　is　767　cycles,　which　can　be　substantially　improved　by　5.43　times　to　4165　cycles　after　the　optimized　factor　combination　design　based　on　the　presented　method.