Excellent In-air Sintering Performance of Cu Microparticle Paste Enabling Large-Area Cu-Cu Bonding in Power Device and System-Level Packaging

As the continuous increase in power density of power modules in Electric Vehicle (EV) Power Control Units (PCU s), there is an urgent demand for high-performance interconnect materials in power device packaging. To address the limitations of conventional copper pastes, this study, commercial copper micro-particles (Cu MPs) are modified via specialized surface modification technique and reductive additives to enhance the sinterability of the Cu paste, endowing large-area sintered Cu-Cu structures with robust bonding and performance. For joints based on sintered Cu paste prepared with modified Cu MPs, the shear strength reaches as high as 53.6 MPa, compared to 4.4 MPa of sintered Cu paste joints with unmodified Cu MPs. Large-area sintering tests conducted under sintering conditions of 8 MPa pressure and 280°C in air atmosphere demonstrate that the joints achieve a shear strength of 53.6 MPa, and their thermal conductivity reaches 272.9 W/(m.K). The performance comparable to that of silver pastes. Scanning electron microscopy (SEM) observations reveal that the sintered Cu bonding layer exhibits a dense microstructure without large pores and reliable metallurgical bonding is achieved. Fractographical morphology analysis indicates that sintered joints with shear strength above 25 MPa undergo interfacial fracture, while those with shear strength above 30 MPa experience trans-interfacial fracture accompanied by plastic deformation. This Cu paste provides a cost-effective solution for large-area Cu-Cu bonding and holds great potential for replacing silver pastes in power device packaging.