Advances in lead-free electronics soldering

Lead-free soldering has emerged as one of the key technologies for assembling in environmental-conscious electronics. Among several candidate alloys, the Sn-Ag-Cu alloy family is believed to be the first choice with the combination of other alloys such as Sn-Zn-Bi, Sn-Cu and Sn-Bi-Ag. Phase diagrams of lead-free alloy systems have been intensively examined by using careful thermal and microstructural analysis combined with the thermodynamic calculation such as the CLAPHAD method. The Cu6Sn5/Cu3Sn layers are formed at most lead-free solder alloy/Cu interfaces, while Cu-Zn compound layers are formed in the Sn-Zn/Cu system. Growth kinetics of intermetallic layers both in solid-state and in soldering are also discussed. Creep and fatigue phenomena are also reviewed. In many aspects of lead-free soldering, much more work is required to establish a sound scientific basis to promote their applications. (C) 2001 Elsevier Science Ltd. All rights reserved.