Experimental Determination of Time-Independent Elastic-Plastic Behaviour of Solder Joints at High Strain Rates

In order to investigate the time-independent behaviour of solder joints at high strain rates, a test setup was created capable of measuring the force vs. time reaction of small solder joint in shear loading at strain rates between 10 ^-1 - 10⁴ [1/s]. The paper describes the design of this high strain rate tester. Details providing for the fast and high resolution force measurement are given. The results of analytic and FEM analyses applied to optimize the force sensor are presented. The paper also points out the challenges of high strain rate measurements of small solder joints. The validation tests applied alumina chips with five SnAgCu solder joints, which had barrel shape with about 200 mum diameter and stand-off height. The test results show good reproducibility of the force vs. time reactions. They match the benchmark results obtained at moderate shear speeds with existing equipment. In addition, fractographic analysis clearly found the two failure modes, bulk and brittle, that had been expected. Hence, the new test setup seems well suited for the tasks it has been designed for.