Epoxy　molding　compounds　(EMCs)　are　widely　used　in　encapsulation　of　various　semiconductor　devices.　QFN　package　has　been　widely　accepted　in　electronic　packaging　industry　in　recent　years　due　to　due　to　its　smaller　dimension,　excellent　thermal　and　electrical　performance.　In　this　study,　the　tensile　tests　based　on　Dynamic　Mechanical　Analyzer　(DMA)　experiment　are　employed　to　investigate　the　viscoelastic　behavior　a　commercial　EMC　material.　FEM　is　used　to　analyze　the　effect　of　EMC　viscoelasticity　by　EMC　constant　elastic　and　viscoelastic　model　based　on　generalized　Maxwell　model　and　WLF　equation.　The　results　show　the　difference　of　von　Mises　stress　for　EMC　elastic　and　viscoelastic　material　models　is　not　obvious　while　equivalent　plastic　strain　reveals　very　significant　difference.　The　predicted　fatigue　life　of　QFN　package　is　underestimated　about　45%　if　EMC　is　assumed　to　be　elastic　instead　of　viscoelastic.　It　is　necessary　to　perform　viscoelastic　analysis　during　the　prediction　of　fatigue　life.　©　2015　IEEE.