Alternating　current　will　lead　to　more　complex　phenomenon　in　electromigration　(EM)　compared　to　one　directional　current,　in　terms　of　the　different　controlling　mechanisms.　Therefore,　Sn-based　joints　will　exhibit　unique　characteristics　of　electromigration　under　reversed　current　stressing.　Eutectic　SnBi　solder　was　used　as　the　main　research　object　in　the　current　study.　The　ambient　temperature　was　set　to　50°C,　and　the　DC　current　input　was　5A,　leading　to　a　corresponding　current　density　of　104A/cm2　during　the　EM　test.　Bi　was　observed　to　be　segregated　along　the　anode　side,　which　was　considered　to　be　the　dominant　diffusing　element　during　the　whole　reversed　current　testing　process.　The　polarity　effect　of　interfacial　intermetallic　compounds　(IMC)　also　existed　in　whole　reversed　current　testing　process.　During　the　one　directional　EM　process,　phase　segregation　can　be　observed　with　obvious　phase　coarsening　effect,　where　Bi　and　Sn　continuous　phases　were　formed　at　the　anode　and　cathode,　respectively.　During　the　reversed　EM　process,　the　initial　continuous　phase　in　the　eutectic　SnBi　solder　joints　migrated　towards　the　opposite　direction　and　finally　disappeared.　The　thickness　of　continuous　phase　was　inversely　proportional　to　the　rate　of　migration,　but　the　average　sizes　of　phase　were　reduced.　©　2011　IEEE.