Low temperature Cu bonding with large tolerance of surface oxidation

A novel method of low temperature all-Cu bonding was developed, which has a large tolerance for Cu surface oxidation and can even bond Cu with a thick oxide layer at 250 °C. It is significant for the chip level bonding because traditional methods have strict requirements for surface quality. The key process is to combine Cu nanoparticle paste and Pt-catalyzed formic acid vapor, which improved the bonding strength of oxidized-Cu by ∼78.5% and is expected to simplify the bonding process. To understand the mechanisms, interfacial analyses of the microstructure and composition were carried out, along with a surface analysis.