Micro-bulk fatigue testing developed to investigate the fatigue lives and damage mechanisms of Sn-3.0Ag-0.5Cu and Sn-37Pb solder alloys. The fatigue life of micro-bulk solder obeyed Manson-Coffin's empirical law, and the fatigue ductility exponents were about 0.5 for both Sn-Ag-Cu and Sn-Pb alloys. The fatigue life of Sn-3.0Ag-0.5Cu alloy was 10 times longer than that of Sn-37Pb alloy under symmetrical cycling at 298 K, although fatigue resistance of Sn-3.OAg-0.5Cu alloy was not very superior under asymmetrical wave and elevated temperature condition. The fatigue crack was developed from extrusion and intrusion of slip band in Sn-3.0Ag-0.5Cu alloy, while the crack was observed at colony boundary and grain boundary in Sn-37Pb alloy. The difference in damage mechanism may affect the susceptibility to fatigue life test condition of reversibility.
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