Formation of a nano-porous structured Cu layer by selective etching of a brass layer and sinter-bonding to achieve direct Cu–Cu bonding

A nano porous structured (NPS) Cu layer was fabricated by a Zn plating-annealing-selective etching process. Furthermore, sinter-bonding was performed by thermocompression after forming the NPS Cu layer instead of the conventional paste sinter-bonding process. The sinter-bonding produced a dense Cu–Cu joint with minimal oxidation by infiltrating the reducing agent into the NPS Cu layer. Sinter-bonding was performed with under a pressure of 5 MPa at 300 °C in air, and excellent bonding strength of 27 MPa was achieved after a bonding time of 1 min. Moreover, the bonding strength increased to 35 MPa by bonding for 1 min while blowing N₂. The optimal thickness of the NPS Cu layer for short-duration sinter-bonding was established, and the oxidation of Cu was suppressed by the infiltration of a reducing agent. Consequently, an excellent shear strength was achieved by sinter-bonding using the NPS Cu layer.