Solderless bonding with nanoporous copper as interlayer for high-temperature applications

The Cu₄₀Al₆₀ alloy has been developed as the precursor alloy to fabricate nanoporous copper (NPC) sheets through chemical dealloying in 1.6 mol/L dilute hydrochloric acid solution at various temperatures. A nanoporous structure with uniform pore distribution and size formed after the bath temperature exceeded 80 °C. The Cu–Cu interconnection was achieved by inserting the NPC sheet as an interlayer and reflowing without solder under a pressure of 10 MPa. After bonding, the thickness of NPC layer was greatly reduced and the porous structure was densified. The average shear strength of the bondlines was measured to be 22.10 MPa, and the bondlines exhibit a low electrical resistivity of 9.65 μΩ·cm. The Vickers hardness and shear strength of the bondline increased after aging at 150 °C for different time due to the densified porous structure. This work demonstrated that the NPC sheets can be used to achieve the Cu–Cu interconnection, which is a potential bonding technology for power devices operating at high temperature.