Comparison of drop performance between the Sn37Pb and the Sn3.8Ag0.7Cu solder joints subjected to drop test

Abstract

This study was concerned with the drop performance between the Sn37Pb and the Sn3.8Ag0.7Cu (wt. %) solder joints when the specimens were subjected to drop test after soldering process. The U-notch butt-jointed specimen was adopted and a lab-designed drop tester was employed. Meanwhile, the electrical resistance values of two kinds of solder joints were measured and recorded after certain drop tests, and finally drop number versus resistance curves were plotted and compared. From the resistance variation with the drop number, it was observed that the Sn37Pb joints presented significantly higher drop performance than the Sn3.8Ag0.7Cu ones. For the Sn3.8Ag0.7Cu specimens, the average drop number before failure was approximately 15-18 and then the resistance values sharply increased. However, the average drop number of the Sn37Pb joints was over 110 and the increasing rate of the electrical resistance was smooth, which is consistent with the results of the board-level drop test. Moreover, one specimen of each kind was picked out and the microstructural observation was carried out to investigate the joint deformation behavior in the dynamic load. It was obvious that the plastic deformation capacity of the Sn37Pb joints was remarkably higher than the one of the Sn3.8Ag0.7Cu joints, proving that most of SnAgCu-based solders presented low deformation compatibility and low energy absorption.