In　the　present　work,　effect　of　adding　small　amount　of　Er　on　the　microstructure,　physical　and　mechanical　properties　of　Sn3.8Ag0.7Cu　solder　has　been　investigated.　The　purpose　is　to　understand　if　the　heavy　rare　earth　Er　has　similar　effect　as　light　rare　earth　Ce　or　La　on　improving　properties　of　SnAgCu　lead-free　solder.　The　results　indicated　that　adding　small　amount　of　Er　can　evidently　improve　the　wettability,　mechanical　strength　and　creep　rupture　life　of　the　Sn3.8Ag0.7Cu　solder　alloy.　It　is　pointed　out　that　proper　Er　content　in　the　Sn3.8Ag0.7Cu　solder　alloy　should　be　in　a　range　of　0.05-0.25　wt%.　Moreover,　the　size　of　intermetallic　compounds　(IMC)　was　measured　quantitatively　for　the　Sn3.8Ag0.7Cu　solder　alloys　with　various　Er　contents.　It　is　felt　that　the　increase　in　mechanical　strength　may　be　related　to　the　refining　of　IMCs　of　the　solder　due　to　the　addition　of　small　amount　of　Er.　(C)　2007　Published　by　Elsevier　B.V.