It　is　known　that　rare-earth　elements　exhibit　high　chemical　activity　and　adding　trace　amount　of　rare-earth　Y　in　the　solder　can　significantly　improve　the　properties　of　solder　alloy.　However,　adding　excessive　rare-earth　Y　in　the　solder　will　result　in　rapid　growth　of　tin　whiskers.　The　research　results　show　that:　if　the　YSn3　precipitates　formed　in　the　interior　of　Sn3.8Ag0.7Cu1.0Y　were　exposed　to　the　air,　YSn3　precipitates　will　oxidize　and　expand　in　volume,　and　the　tremendous　compressive　stress　produced　by　the　surrounding　solder　matrix　constraining　the　volume　expansion　will　accelerate　the　growth　of　tin　whiskers.