Bismuth　telluride-based　thermoelectric　devices　have　attracted　much　attention　in　the　field　of　low-quality　waste　heat　recovery　below　200　°C.　However,　the　rapid　diffusion　at　the　interface　between　solder　and　thermoelectric　materials　was　serious　after　long-term　service.　The　brittle　Sn-Te　was　believed　to　cause　the　electrode　failure.　In　this　work,　it　suggested　that　the　regional　eutectic　melting　at　the　β-Sn/SbSn　interface　at　hot-end　electrode　was　a　more　important　risk　to　cause　the　failure,　requiring　urgent　attention.　Co-diffusion　of　Bi　and　Sb　led　to　partial　melting　of　the　Sn-based　solder,　which　did　not　wet　on　the　SbSn　surface　and　formed　solidification　cracks.　Besides,　the　distributions　and　migrations　of　Bi,　Sb,　Te,　and　Sn　elements　at　the　interface　were　investigated,　the　crystal　growth　direction　of　SnTe,　SbSn,　and　nano-Bi　phases　were　analyzed,　and　the　phase　composition　and　phase　evolution　in　complex　intermetallic　compounds　(IMCs)　at　the　Bi-Sb-Te/Sn　interface　were　clarified,　combined　with　SEM,　EPMA,　and　TEM　characterization　during　the　aging　at　150　°C　for　150　h.　Based　on　this　failure　mechanism,　it　suggested　that　the　service　temperature　should　be　lower　than　the　Sn-Bi　eutectic　temperature　and　as　low　as　possible,　in　the　case　of　without　any　coating　treatment　for　the　consideration　of　cost.　©　2023　Elsevier　B.V.