Comparison of Impact Toughness and Fracture Morphologies Between Pb-Containing and Pb-Free Solder Joints Subject to the Charpy Impact Test

摘要

Charpy impact tests on three kinds of as-soldered U-notch specimens were performed with reference to the American Society of Testing Materials (ASTM) standard E23-07 by using a pendulum-type impact tester at room temperature. Three kinds of solders, conventional Sn-37Pb, Sn-3.8Ag-0.7Cu, and Sn-3.8Ag-0.7Cu doped with rare-earth (RE) elements, were selected to fabricate the joint specimens for the impact test. The three joints demonstrate similar impact toughness values, with averages of 11.4 kJ/m~(2), 10.4 kJ/m~(2), and 11.0 kJ/m~(2), respectively. Under observation by scanning electron microscopy (SEM), the Sn-37Pb joint exhibited mainly ductile fracture morphology. Fractographic observations of lead-free joints exhibited a mixture of ductile and brittle morphologies. The addition of RE elements resulted in an impact toughness that was slightly higher than that of the Sn-3.8Ag-0.7Cu alloy. The impact toughness and the fracture mode were notably dependent on the type of solder. Additionally, the thickness of the intermetallic compound (IMC) layer had a remarkable influence on the fracture path and impact toughness of the solder joints.