Partially Liquid Interconnects With The Au–Ge System – Mechanical Strength and Electrical Resistivity

Abstract

Off-eutectic Au–Ge, $10 \pm 2$ at.% Ge, were formed between Au metallized Si substrates to investigate their high temperature compatibility. High quality joints made with a small bond pressure, 53 kPa, were fabricated. The joints comprised three different types of morphologies; (1) a layered structure of Au / Au–Ge / Au, (2); a layered structure of Au / Au–Ge / Au where some sections of the central Au–Ge band were replaced by a Au section that extended across the joint, and (3); a roughly homogenous Au layer. Joints formed with a higher bond line pressure, 7.6 MPa, were of a reduced quality with voids and cracks at the original bond line. The shear strength of the fabricated joints was found to be at least 50 MPa, and the fracture mode was an adhesive fracture at the adhesion layer. The effective melting point were found to be at least 460°C, or 100°C above the eutectic isotherm of the binary Au–Ge system. Electrical resistivity measurements confirmed a melting process at the eutectic isotherm by an abrupt increase in resistivity.