Effect of Oxygen Content on Bonding Performance of Sintered Silver Joint on Bare Copper Substrate

Abstract

Optimizing oxygen level in sintering atmosphere seems to be a more economical method to realize die-attachment on bare copper substrate with silver paste. In this paper, effects of oxygen content on mechanical and thermal performance of sintered Ag joint on bare copper substrate were investigated. The 5×103 ppm was demonstrated as the most appropriate oxygen content for the optimum bare copper joint, which removed most organics in the paste layer while preventing copper substrate from oxidation. Besides, bonding mechanism of joints sintered under different oxygen levels was clarified. For joint sintered at 1×103 ppm, excess residual organics significantly facilitated the formation of hydrogen bonds, resulting in the adhesive-dominated failure mode and worst overall performance. The increase of oxygen content to 5×103 ppm reinforced the bonding strength due to the Ag-Cu metallic bond formation at the interface and ameliorative densification of sintered-Ag layer. As the amount of oxygen further increased, copper substrate was oxidized, and bonding strength experienced a changing course of decline, rise, and flat, which can be attributed to Ag adhesion on copper surface and the formation of voids at the interface between oxide layer and copper substrate.