Laser sintering mechanism and shear performance of Cu-Ag-Cu joints with mixed bimodal size Ag nanoparticles

In order to obtain Ag nanoparticles (NPs) sintered Cu-Cu joints with better mechanical properties in a relative short time and under a suitable pressure, a laser sintering process and a novel paste prepared by mixed Ag NPs (19 and 62nm in diameters) were utilized and studied. The results indicated that joints with low porosities were fabricated within 15 s' laser irradiation. By increasing laser power and sintering time, shear strength of the joints increased obviously. Shear strength of joints with 30% (mass ratio) 62nm NPs was the highest and could reach 32MPa when the samples were sintered at 60W for 15s under 5MPa. The enhanced mechanical properties of the joints could be attributed to small NPs that could fill pores between larger NPs and improve initial packing density of the mixed particles. The results indicated that the mixed pastes had excellent potentials as alternative die-attach materials for high temperature power device applications.