Dynamic constitutive behavior of eutectic solder at strain-rates up to 200 s^-1

The mechanical reliability of lead-tin and lead-free solder joints under shock loading conditions is relevant to a wide range of electronic applications ranging from personal cellular phones to smart weapons. Prior studies on the dynamic constitutive properties of solder alloys have been largely limited to two regimes: conventional tests at strain rates <1/s and split-Hopkinson pressure bar tests at strain rates >500/s. A gap exists in the intermediate rate regime which is directly applicable to failure events that occur over ∼1-100 ms durations. A recently developed high-rate servohydraulic method has been employed to characterize the temperature and strain-rate dependent stress-strain behavior of eutectic Pb-Sn solder alloys over a wide range of strain rates (10-4 to 102 /s) and temperatures (-60°C to +100°C). As expected, the alloys are strongly strain-rate sensitive. For example, at 100°C, the yield strength of eutectic Pb-Sn solder increased from 5 MPa at 0.0002 /s to 42 MPa at 200 /s. We found that the common Johnson-Cook model does not adequately capture the temperature and strain-rate dependent constitutive behavior of these alloys. ©2009 Society for Experimental Mechanics Inc.