Evaluation of the joint strength between Sn–3.0Ag–0.5Cu solders and Cu substrate at high strain rates

A lack of study on the dynamic tensile strengths of Sn-based solder joints at high strain rates was the motivation for the present study. A modified miniature Chapy impact testing machine instrumented with an impact sensor was built to quantitatively evaluate the dynamic impact strength of a solder joint under tensile impact loading. This study evaluated the tensile strength of lead-free solder ball joints at strain rates from 1.8×103 s−1 and 8.5×103 s−1. The maximum tensile strength of the solder ball joint decreases as the load speed increases in the testing range. This tensile strength represented that of the interface because of the interfacial fracture site. The tensile strengths of solder joints between Sn–3.0Ag–0.5Cu and copper substrate were between 196.2 MPa and 72.1 MPa in the high strain range. The brittle interfacial fracture was likely to occur primarily in the waist of the protuberant Cu6Sn5 intermetallic layer. The fracture toughness values of interfacial IMC (intermetallic compound) between Sn–3.0Ag–0.5Cu and copper substrate were between 1.8 MPa m0.5 and 1.0 MPa m0.5 in the speed range tested.