In　Package-on-Package　(PoP)　manufacturing,　warpages　on　both　top　and　bottom　packages　are　concerned.　Excess　warpage　causes　solder　joint　opening,　and　results　in　the　electrical　connection　failure　of　the　assembled　module.　Many　parameters　of　materials,　geometry,　and　process　contribute　to　the　warpage　of　the　package.　The　objective　of　this　paper　is　to　investigate　effects　of　these　parameters　on　the　warpage.　The　dimensions　of　dies,　package　and　substrate,　materials　of　molding　compound　and　substrates　are　investigated　by　the　finite　element　method　(FEM)　in　the　processes　of　molding　and　reflow.　After　running　simulation,　analysis　of　variance　is　employed　to　identify　the　influential　parameters.　The　results　show　that　the　coefficient　of　thermal　expansion　(CTE)　of　molding　compound　and　substrate　as　well　as　die　sizes　have　significant　influence　on　the　warpage.　Based　on　this　study,　the　influential　parameters　can　be　optimized　within　practical　range　to　achieve　the　lowest　warpage　value.