Development of Robust Oxidation-Free Cu-Cu Direct Bonding with Micron-Sized Cu–Ag Salt Composite Paste and Deterioration Mechanism During Aging and Power Cycling

Abstract

Abstract- The development of next-generation power electronics requires the semiconductor power devices with higher voltage endurance, higher electrical current density under high-temperature operations above 250°C. Herein, we propose the uses of combined micron-sized Cu particles with Ag–amino composite to achieve a robust direct Cu–Cu bonding under a low sintering pressure and temperature (300°C) in ambient atmosphere. The strong bonding strength of the Cu–Cu joint structure was evaluated as high as 45.3 MPa under 300°C sintering temperature with low pressure (1 MPa). For the high　temperature reliability evaluation, the sintered Cu-Ag salt composite Cu-Cu joints were stored at 250 °C in air; the shear strength of the joints remains above 30 MPa after 500 h ageing, suggesting an excellent mechanical stability during high temperature storage. Additionally, a SiC Schottky barrier diode with the sintered Cu–Ag salt composite joint structure was evaluated during a power cycle test at a junction temperature of 200°C for 10,000 cycles. The thermal resistance of the joint structure was almost unaffected, and no large delamination in the bonding layer was observed after the power cycle test, indicating that the Cu–Ag composite joints as a die attach material exhibit remarkable potential in SiC power devices packaging.

Keywords: Direct Cu bonding, sintering, Cu-Ag composite paste, anti-oxidation, SiC electronic packaging, high temperature reliability