Improvement of high-temperature thermal aging reliability of Ag–Au joints by modifying Ni/Au surface finish

Sintering Ag paste on Ni/Au surface finish (Ag–Au joint) is a hot topic because Ni/Au surface finish is one of the most commonly used metallizations in the electronics industry. However, it is still difficult to achieve a reliable Ag–Au joint after high-temperature thermal aging due to severe Ag–Au interdiffusion. In this work, we investigated thermal aging reliability of Ag–Au joint via high-temperature storage at 250 °C up to 1000 h. The Ag–Au joints with 0.1 and 0.8 μm Au layer coated substrates were compared to study the Au layer thickness effect on thermal aging reliability of joints, and a substrate preheating treatment was proposed to improve thermal aging reliability of Ag–Au joint. The result clearly shows that preheating treatment can improvement of bonding performance including thermal aging resistance and initial shear strength for both the thickness of Au layer. The shear strength of 1000 h thermally aged Ag–Au joint with the 0.1 and 0.8 Au substrate has been further improved to 11.7 and 16.5 MPa via the substrate preheating treatment, respectively. The substrate preheating treatment can lead to further growth of Au grains by eliminating fine grains, which results in the improvement of thermal aging reliability of joints. In addition, the thicker Au layer showed superior thermal aging reliability. This is attributed to the thicker Au layer less susceptive to massive Ag–Au interdiffusion and can prohibit severe oxidation of Ni because it hosts larger Au grains and fewer grain boundaries. The study would provide a convenient way to improve the thermal aging reliability of Ag–Au joints.