FRACTURE-BEHAVIOR OF 63SN-37PB SOLDER

The isothermal mechanical and fracture mechanics material properties of 63Sn-37Pb solder were determined at -55,24 and 125°C ( -67,75 and 257°F). Tensile, creep-rupture, fracture toughness, fatigue crack growth rate (FCGR) and creep/FCGR tests were performed. Specimen fracture surfaces were examined using scanning electron microscopy and Auger spectroscopy. The fracture toughness of 63Sn-37Pb solder was greater at -55°C (-67°F) than at 24°C (75°F). Ductile transgranular fracture was observed at -55°C (-67°F) while ductile intergranular fracture was observed at room temperature. The presence of intergranular facets at 24°C (75°F) corresponded to the lower fracture toughness and J resistance curve slope demonstrated by the 63Sn-37Pb solder compared with the low temperature results. The growth rate of fatigue cracks in 63Sn-37Pb solder decreased with a decrease in temperature over the temperature range of 24 to -55°C (75 to -67°F) and, at room temperature, was insensitive to frequency over the frequency range of 2-10 Hz. Crack closure did not influence the near-threshold FCGR behavior of 63Sn-37Pb solder. The fatigue fractures developed under these model laboratory conditions exhibited some similarities to the features characteristic of leadless chip carrier/printed wiring board solder interconnector failures. The results of such model studies can be used to assist analyses of solder failures but other factors including solder thermal expansion and mechanical constraints can greatly impact solder behavior and must be recognized in the analyses. © 1990.