Architecting core–shell Si3N4@CuO interfaces to resolve nanoparticle agglomeration and dramatically elevate the shear strength of Sn58Bi solders

To address the issues of agglomeration and weak interfacial bonding of Si 3 N 4 particles within the solder, core–shell structures were introduced to enhance the performance of the Si 3 N 4 particles. A series of Si 3 N 4 @CuO x (SC x ) particles ( x = 0, 1, 2, 3, 4) was prepared by coating CuO thin films onto the Si 3 N 4 particles, and the effects of these SC x particles on the properties of Sn58Bi solder were evaluated through experimental characterization. Experimental results indicated that SC particles, while retaining the advantages of Si 3 N 4 NPs, were also embedded more uniformly within the solder matrix. This led to the introduction of more grain boundaries and dislocations, thereby improving the microstructure and mechanical performance of the solder joints. However, a higher Cu content in the SC particles led to their accumulation above the intermetallic compound (IMC) layer, adversely affecting joint properties. Among all the tested samples, the Sn58Bi-SC3 solder joint exhibited the best overall performance, achieving a shear strength of 67.9 MPa, a 62.8% increase over the SC particle-free solder joint.