Basic　understanding　of　heating　conduction　in　lead-free　solder　joints　due　to　the　Joule　heating　effect　was　carried　out　by　using　the　infrared　(IR)　microscopy.　In　order　to　interpret　the　corresponding　mechanism　and　provide　a　better　understanding　to　Electromigration　(EM)　studies,　a　newly　developed　ID　solder　joint　with　same　cross-sectional　area　in　solder　alloy　and　Cu　electrodes　was　employed　in　our　thermal　imaging　analysis.　Both　eutectic　SnBi　and　SnAgCu　solder　alloy　were　used　to　fabricate　the　joints　due　to　their　distinct　electrical　resistivity　and　thermal　conductivity.　Various　electrical　current　inputs　combined　with　joints＇　thickness　of　500　urn　were　investigated.　Accordingly,　transient　and　steady-state　heat　conduction　were　identified　and　compared　with　different　experimental　conditions.