Correlation of uniaxial tension-tension, torsion, and multiaxial tension-torsion fatigue failure in a 63Sn-37Pb solder alloy

Solder joint failure in surface mount technology applications occurs due to shear-dominated multiaxial strain-controlled fatigue. The authors investigate the multiaxial fatigue of solders and determine the feasibility of predicting the multiaxial fatigue behavior of solder alloys from the existing uniaxial experimental database. Isothermal uniaxial and multiaxial room-temperature total strain-controlled fatigue tests were conducted on bulk near-eutectic 63Sn-37Pb specimens at a frequency of 0.5 Hz. Fatigue surface examination indicated that cracking of the tin phase and separation of the tin-lead interface were the dominant fatigue failure mechanisms in this solder alloy regardless of the loading. A number of models for predicting mixed-mode fatigue lifetimes from uniaxial data were investigated. The present set of fatigue lifetime data for 63Sn-37Pb solder for uniaxial and tension torsion differed by a factor of 3.1 or less on the basis of several of these models. The maximum plastic shear strain was the best overall parameter to use in a Coffin-Manson-type plot with all data differing by no more than a factor of 2.8 from the uniaxial tension data