Test Methodologies to Perform Valid Accelerated Thermomechanical Fatigue Tests of Solder Joints

Valid test parameters for performing thermomechanical fatigue tests are needed to make reasonable life prediction estimates for solder joints in electronic assemblies. We present the results of three test parameters that can be used to perform accelerated thermomechanical fatigue tests: deformation rate, hold time, and atmosphere. At deformation rates of 2.8 × 10^-4 s^-1 and slower, the damage mechanism in the solder does not change and is in the form of heterogeneous coarsening at cell boundaries, indicating that this is a valid testing rate. Decreasing the hold time at the temperature extremes to the point where the stress relaxes to zero at the high-temperature portion of the thermal cycle results in the same solder joint behavior as longer hold times. Accelerating the test by changing environment was found to change the damage mechanism and is not a valid means of accelerating thermomechanical fatigue tests for solder joints.