Fracture behavior and mechanical strength of sandwich structure solder joints with Cu–Ni(P) coating during thermal aging

Abstract

Coating at the interface of solder joint has a great impact on the growth behavior of intermetallic compounds (IMCs) and the mechanical properties. In this study, the sandwich structure samples of Cu/Sn3.0Ag0.5Cu/Cu solder joints with coatings of Ni(P) monolayer and dual Cu-Ni(P) layers on Cu substrate were designed to conduct the shear test. The mechanical strength, fracture modes, and fractographic morphologies of Sn3.0Ag0.5Cu/Cu, Sn3.0Ag0.5Cu/Ni(P)-Cu, and Sn3.0Ag0.5Cu/Cu-Ni(P)-Cu solder joints reflowed at 280 °C for 10 min and then aged at 150 °C for up to 360 h were investigated. Experimental results show that the mechanical strength of Sn3.0Ag0.5Cu/Cu solder joints firstly increased because of the pinning effect of IMC, and then decreased due to the brittleness of excessive growth of IMC during solid-state aging processes. The Sn3.0Ag0.5Cu/Cu solder joints presented ductile fracture, mixed fracture, and brittle fracture modes during shear testing processes. The shear strength of Sn3.0Ag0.5Cu/Ni(P)-Cu solder joints decreased to about 17 MPa after 120 h thermal aging. At the same time, the shear failure mode of Sn3.0Ag0.5Cu/Ni(P)-Cu solder joints changed from the ductile dominant fracture to the brittle dominant fracture. The shear strength of Sn3.0Ag0.5Cu/Cu-Ni(P)-Cu solder joints remained approximate 21 MPa and the fractured position always occurred inside the IMC layer regardless of aging time.