Large-Area Substrate Bonding With Single-Printing Silver Paste Sintering for Power Modules

Sintered silver with high thermal conductivity and reliability has been considered as a promising substrate bonding solution in power modules. The traditional double printing process is complex, and the second layer of silver paste is too thin to ensure complete wetting. We greatly simplified the sample preparation process by single printing and optimized the sintering process by means of open-face contact drying technology and staged heating method. In this article, the effect of predrying steps and heating rate on the quality of sintered silver joint on large area silver-plated DBC substrate and its mechanism are discussed. The microstructure shows that the samples sintered by the optimized sintering process have no obvious defects, and the sintered silver layer is dense and uniform. In order to evaluate the bonding quality of the whole joint, the sample was cut into 16 small pieces by metallographic cutter, the average shear strength was 55.65 MPa, and the strength distribution between the center and the edge of the sample was uniform. The samples sintered by an optimized sintering process show cohesive failure mode and typical ductile fracture morphology. The energy dispersive spectrum analysis shows that the composition distribution of the sintered silver layer in the center and edge of the sample was relatively uniform, which is consistent with the distribution of shear strength. The scanning electron microscopy image of cross section demonstrated that the porosity of the adhesive layer is 3.08%, which is far lower than that of the traditional double printing process, with good interface bonding and no delamination.