Modern　market　requires　smaller　products　with　more　functionalities　which　are　driven　by　high　speed　Package　Circuit　Boards　(PCBs)　and　Integrated　Circuit　(IC)　packages.　Thermal　control　of　PCBs　and　IC　packages　is　challenging　in　microelectronics　because　the　power　density　increases　when　smaller　and　more　complicated　packages　are　designed.　Temperature　rise　due　to　power　dissipation,　hotspot　worsens　harmful　clock　skew,　jeopardizes　reliability　of　products.　To　overcome　these　risks,　PCBs　and　IC　packages　designers　have　to　perform　electromagnetic-thermal　co-simulations　at　the　early　design　stage.　Usually　the　temperature　rise　of　the　whole　package　is　easy　to　be　calculated,　it　is　difficult　to　detect　the　hotspots　in　the　package　due　to　local　high　current　density　because　very　high　resolution　simulations　are　needed.　In　this　paper,　an　improved　adaptive　finite　element　method　(FEM)　is　applied　to　detect　hotspots.　This　method　only　requires　one　step　adaptive　refinements　in　every　FEM　solution　for　a　given　error　threshold　in　the　hotspot　detection　progress,　so　that　it　is　very　fast　and　uses　much　smaller　computation　resources.　Test　results　show　that　the　adaptive　FEM　only　uses　about　60　times　memory　and　CPU　time　to　detect　all　hotspots　in　the　package　comparing　to　the　initial　FEM　solution.　©　2011　IEEE.