Fabrication of Nanoporous Cu Sheet and Application to Bonding for High-Temperature Applications

Nowadays, several joining processes are proposed as alternatives to high-Pb-containing solders. There are many reports on bonding techniques using metal nanoparticles, and 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, some reliability concerns exist, such as the formation of undesired voids and gaps caused by the residue solvent. To address this issue, a bonding technique without solvents using a nanoporous sheet has been proposed. In this study, nanoporous Cu sheets were fabricated by dealloying of Cu-Mg alloy in a hydrochloric acid solution and effects of the nanoporous Cu structure on the bonding strength and long-term reliability were investigated. The results show that the joints bonded at 350°C, using the nanoporous Cu sheet dealloyed for 300 s have high shear strength of over 40 MPa. Moreover, the shear strength of the joint aged at 250°C for 1008 h remains over 30 MPa, revealing its long-term reliability. Hence, the proposed joining process using nanoporous Cu sheets has great potential for high-temperature applications.