Effect of Au nanoporous structure on bonding strength

Recently, several materials and joining processes have been proposed as alternatives to high-Pb-containing solders. There has been an increasing focus on developing solid-state bonding interconnection processes based on sintering, such as bonding techniques using Ag or Cu nanoparticles. However, sintered nanoparticle layers tend to have voids that result from solvent residue and dispersing agents. The voids in the sintered layer degrade the reliability of the joints. Therefore, we have proposed a solid-state bonding technique without solvents and flux using a nanoporous sheet. A nanoporous sheet can be made from binary alloy systems by dissolving the less noble component from the alloy selectively. A bonding technique using nanomaterials could reduce the bonding temperature because of the high reactive nanoporous surface. In this study, Au nanoporous sheets were fabricated by dealloying a Au-Ag alloy into an HNO₃ solution, and the effects of the Au nanoporous structure on joint bonding strength were investigated. After dealloying, Au nanoporous sheets were set between bare Cu substrates. The samples were bonded at various process temperatures under a nitrogen atmosphere. As a result, the joint bonded at 300 °C, using the Au nanoporous sheet with a dealloying time of 1 h, showed a high shear strength of about 20 MPa. It was found that joining using Au nanoporous bonding was successfully achieved.