Fabrication of high reliability Cu joints at low temperatures using synergistic effect of organic composition for power device packaging

Copper paste sintering has great potential for WBG (wide bandgap) semiconductor packaging, but the problems of copper susceptibility to oxidation and high sintering temperatures have hindered its development. A micron copper paste suitable for low-temperature sintering was successfully formulated using the synergistic effect of metal organic decomposition (MOD) ink and ascorbic acid (AA) to achieve high shear strength sintered joints. During the sintering process, AA acted as a reducing agent to effectively remove oxide on the surface of the Cu microparticles (MPs), while the decomposition process of MOD was facilitated by the reduction products. The diffusion channels formed by the decomposed nanoparticles connect the Cu-MPs, forming dense sintered joints. At a sintering temperature of 250 °C, the combination of MOD and AA in the paste resulted in a significant improvement in the shear strength of the sintering joints, reaching 102.2 MPa. This is in contrast to the addition of only MOD or AA, which resulted in a shear strength of less than 5 MPa. Furthermore, the strength of the sintered joints was increased to 128.1 MPa after storage at 250 °C for 1000 h. At a sintering temperature of 210 °C, the strength could still reach 47.6 MPa, which was approximately double the strength of traditional Sn-based solder joints. This has greater practical significance for the fabrication of high-strength bonded joints and the expansion of the sintering process window.