Whisker　formation　is　a　frequently　occurring　problem　in　the　electronica　industry,　causing　damage　to　fine-pitch　electrical　components.　Several　theories　and　models　have　been　developed　to　describe　the　whisker　growth,　and　many　attempts　have　been　made　to　find　solutions　for　this　issue.　Most　of　the　previous　literature　addressed　the　formation　of　Sn　whiskers,　while　some　attention　was　focused　on　Bi-rich　whiskers.　Moreover,　investigation　of　different　types　of　whiskers　would　be　beneficial　for　understanding　of　the　fundamental　processes　behind　of　the　whisker　growth.　In　our　work,　we　analyze　and　discuss　the　growth　of　Bi-rich　whiskers　in　eutectic　Sn58Bi　solder　coatings　under　isothermal　aging　conditions.　A　possible　growth　mechanism　for　Bi-whiskers　in　the　coating　is　proposed.　Two　processes　contributed　to　the　whisker　growth.　One　process　was　the　chemical　reaction　between　Cu　and　Sn　atoms　to　form　Cu6Sn5.　Cu　atoms　were　inexhaustibly　introduced　into　the　coating　from　the　substrate　and　caused　the　formation　of　Cu6Sn5.　This　process　provided　the　driving　force　and　was　a　sufficient　condition　for　the　growth　of　Bi-rich　whiskers.　The　second　process　was　the　segregation　of　Bi　atoms　driven　by　the　gradient　of　the　Bi　atoms＇　concentration.　This　process　was　the　necessary　condition　for　Bi-whiskers　growth.