Time-independent mechanical and physical properties of the ternary 95.5Sn-3.9Ag-0.6Cu solder

The development of a constitutive model for predicting the thermal-mechanical fatigue (TMF) of 95.5Sn-3.9Ag-0.6Cu (wt.%) Pb-free solder interconnects requires the measurement of time-independent mechanical and physical properties. Yield stress was measured over the temperature range of -25-160degreesC using strain rates of 4.2 x 10(-5) s(-1) and 8.3 x 10(-4) s(-1). The yield-stress values ranged from approximately 40 MPa at -25degreesC to 10 MPa at, 160degreesC for tests performed at 4.2 x 10(-5) s(-1). The faster strain rate and specimen aging had a limited impact on the yield stress. The true stress/true strain curves indicated that dynamic-recovery and dynamic-recrystallization processes took place in as-east samples exposed to temperatures of 125degreesC and 160degreesC, respectively, while tested at a strain rate of 4.2 x 10-5 s(-1). Aging the sample prior to testing, as well as a faster strain rate, mitigated both phenomena. Dynamic Young's modulus values ranged from 55 GPa at -50degreesC to 35 GPa at 200degreesC, while the coefficient of thermal expansion (CTE) increased from approximately 12 x 10(-6o)C(-1) to 24 x 10(-6o)C(-1) for the same temperature range. The aging treatment had little effect on either Young's modulus or the CTE.