Prediction of Fatigue Resistance in Lead-Free Ni-Doped SAC 1205 Solder Alloys Using a Rate-Dependent Material Model and Subjected to Drop Tests

In this paper, a novel Ni-doped SAC 1205 (Sn-1.2Ag-0.5Cu) solder alloy is investigated to determine its mechanical behavior at a high strain rate. The Ni-doped SAC 1205 solder alloy has never been discussed in terms of high-strain-rate testing. The purpose of the SAC 1205 solder material doped with Ni is to enhance the mechanism of the solder alloy and delay the formation of the brittle intermetallic compound. In the drop test standard (Joint Electron Device Engineering Council condition B), the test vehicle was subjected to impact loading with a peak acceleration of 1500G and a time duration of 0.5 ms. Because the test board supported the impact loading for a very short time, the solder joint material was considered to have a rate-dependent elastic-plastic behavior. The quasi-static mechanical behavior and dynamic behavior were estimated for the simulation modeling by conducting a quasi-static tensile test and a split Hopkinson tensile bar test. A finite-element model was used to analyze the stress and strain of the solder joint during the drop test. The experimental results revealed that Young's modulus and yielding strength of the Ni-doped SAC 1205 solder alloy increased during the high-strain-rate testing. Therefore, a rate-dependent elastic-plastic model of the Ni-doped SAC 1205 solder alloy was designed and implemented to describe the real mechanical behavior of a solder joint at a high strain rate during a drop test. The primary failure mode occurs at the top of the solder joint (package side) during the drop test. The predicted fatigue model we provided was focused on the primary failure mode. Eventually, the fatigue life curve of the rate-dependent elastic-plastic model offered the greatest accuracy in predicting the solder joint fatigue life.