(111) and (220) preferred-orientation Cu substrates were successfully produced by varying electroplating current-density. While these preferred-orientation Cu substrates reacted with Sn, serious Kirkendall voids formed at the interfaces between Sn and (111) and (220) preferred-orientation Cu substrates. Also, abnormal Cu(3)Sn growth occurs; the Cu(3)Sn layer decreased upon aging and vanished after 1000-h aging. With a prolonged 2000-h aging, a Cu(3)Sn layer re-grew at the Cu(6)Sn(5)/Cu interface. The abnormal Cu(3)Sn growth was found to highly associate with serious Kirkendall formation (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3608248] All rights reserved.