Using nano-porous Au-Ag sheets as a joint layer for low-temperature Au-Au bonding

In this research, we proposed low-temperature Au-Au bonding using nano-porous Au-Ag sheets as a joint layer. The influences of annealing temperature on the porous structure and chemical properties of the sheets were investigated. The nano-porous sheet was fabricated by dealloying a 100 μm thick Au-Ag sheet in solution HNO₃. The nano-porous sheets were annealed between 100 °C and 250 °C. The chemical composition of the sheet was analyzed by using X-ray photoelectron spectroscopy (XPS). Two substrates and nano-porous sheet were bonded under a pressure of 8 MPa for 20 min. Bonding strengths were about 0.5 MPa, 1.0 MPa, 1.8 MPa, and 4.8 MPa at annealing temperatures of 100°C, 150°C, 200°C, and 250°C, respectively. The sheet which had about 10 nm ligament formed on the surface by additional treatment of immersing in liquid nitrogen was also used as a bonding layer. This treatment was effective to increase the bonding strength.