Room-temperature, rapid, solid-state solder bonding technology for future ultra-high-density interconnects manufacturing

Developing ultra-high-density interconnects using current technologies presents certain limitations. It is because traditional solder joint technology employs a liquid-solid interfacial reaction process that makes it difficult to control the shape of the solder joint, thus limiting the size, pitch, and density of interconnects. Although the Cu–Cu direct bonding technique can help fabricate high-density interconnects, its high cost and limited application in consumer electronics present further challenges. In this study, we developed a simple, rapid, and cost-efficient method for fabricating high-density interconnects. We produced homogeneous submicron solder particles as small as 300 nm through ultrasonic treatment. The homogeneous size distribution was achieved by minimizing inter-particle ripening reactions, sluggish diffusion, and low Gibbs-Thomson chemical potential in the medium-entropy Sn–Bi–In-based solder particles. We dispensed the particle solution between two Cu substrates, and they bonded within 5 min at room temperature through a solid-state interfacial reaction. The shear strength of the bonding is around 14.8 ± 1.2 MPa. Our bonding technology shows potential for use in 3D integration to manufacture ultra-high-density interconnects.