Impact of Cryogenic Temperature Environment on Single Solder Joint Mechanical Shear Stability

Abstract

Although the performance of electronic devices in extreme temperature ranges has been extensively studied, the interconnections, which are still mainly Sn-based materials, require thorough observation and assessment to support the mechanical and electrical stability in subzero to cryogenic temperature environments. An in-depth assessment is required because of the nature of Sn, which has a ductile-to-brittle transition temperature of approximately −60°C. Sn-1Ag-0.5Cu (wt.%) (SAC105) solder joints were subjected to shear testing at room temperature and at −196°C at liquid nitrogen temperature. Isothermal aging at 150°C for 50–500 h prior to cryogenic temperature testing indicated further degradation under certain aging conditions. The study presented here investigates the maximum shear strength variations for SAC105 single solder joints with NiAu and Cu-organic solderability preservative (Cu-OSP) pad surface finishes using a multibond tester with a 10-μm shear height and 100-μm/s shear speed. An increase in the maximum shear strength was observed at liquid nitrogen temperature compared to that at room temperature due to an increase in the yield strength and loss in ductility of the solder material in response to the low-temperature environment. The maximum shear strength decreased with isothermal aging due to the crack propagation path variation. Fracture locations were identified between the Ni pad and the (Cu, Ni)₆Sn₅ interface for the NiAu surface finish components, and Cu-OSP surface finish solder joints revealed transgranular crack through the Cu₆Sn₅ and crack propagation between the Cu₆Sn₅ and the solder interface. The shift in the full fracture location is discussed in association with electron backscatter diffraction (EBSD) analysis on partially sheared solder joints at room temperature and at −196°C.