Throughout　the　development　of　electronic　packaging　technology,　Sn-58Bi　lead-free　solder　has　been　widely　applied　because　of　its　low-Temperature　welding.　However,　during　the　production　process,　the　formation　of　solder　bead　is　a　terrible　problem　that　is　commonly　encountered　with　Sn-58Bi　solder　joint.　This　problem　not　only　damages　the　macroscopic　appearance　of　the　solder　joint,　but　may　encompass　other　solder　joints　as　well.　Due　to　factors　such　as　vibration　and　temperature　variation,　the　formation　of　solder　bead　could　potentially　lead　to　circuit　fault.　The　purpose　of　this　study　is　to　investigate　how　the　oxidation　of　Sn-58Bi　solder　powder,　under　different　temperature　and　humidity,　impacts　the　formation　of　solder　bead　and　microstructure　of　the　solder　joint.　The　scanning　electron　microscope　and　auger　electron　spectroscopy　were　used　to　analyze　the　oxidation　process　of　Sn-58Bi　solder　powder.　The　results　indicated　that,　the　formation　of　solder　bead　was　enhanced　with　the　increased　temperature　and　humidity　which　also　led　to　the　deteriorated　microstructure　and　poor　wettability.　In　addition,　the　oxidation　behavior　of　Sn-58Bi　solder　powder　revolved　around　the　adsorption　and　decomposition　of　O　molecules　and　the　subsequent　interaction　between　the　O　atoms　with　the　Bi　atoms.　©　2016　IEEE.