Since　the　packaged　device　is　composed　of　materials　with　different　thermal　properties,　the　package　will　be　subjected　to　multiple　thermal　and　mechanical　loads　during　the　packaging　process,　resulting　in　stress　and　deformation.　The　stresses　may　cause　delamination　or　cracking　of　the　electronic　device　even　before　the　package　processing　is　completed.　Therefore,　it　is　crucial　to　consider　the　process　step　continuity　during　the　packaging　process　to　improve　the　reliability　of　the　packaged　devices.　In　this　paper,　the　three-dimensional　structural　model　of　the　auxiliary　transformer　is　established　by　ANSYS　Workbench　software.　Three　sequential　process　steps,　reflow　soldering,　molding　and　thermal　shock,　are　simulated　using　the　method　of　killing　activating　elements,　and　the　fatigue　life　of　solder　joints　under　thermal　shock　is　predicted　based　on　the　Coffin-Manson　fatigue　model.　The　results　show　that　at　the　moment　of　peak　reflow,　the　stress　at　the　contact　location　between　the　Magnetic　mold　and　the　T-core　of　the　auxiliary　transformer　reaches　a　maximum　value　of　121　MPa,　with　a　possible　risk　of　cracking　failure.　The　predicted　fatigue　life　of　solder　joints　in　thermal　shock　reliability　is　580　cycles.