Sintering performance analysis of conductive silver paste on aluminum alloy surface

A low-temperature sintered conductive silver paste containing Bi₂O₃-B₂O₃-ZnO glass frit was used for sintering thick silver film on the surface of aluminum alloy to realize aluminum alloy soft soldering. First, Bi₂O₃-B₂O₃-ZnO glass with glass transition temperature (T_g) of 360 °C was synthesized by using a melt-quenching method. Then, it was mixed with submicron silver powder to prepare lead-free low-temperature sintered silver paste, which was coated on the surface of 6061 aluminum alloy and sintered at temperatures of 440, 470, 500 and 530 ℃, respectively. The effects of sintering temperature on the resistivity and the solderability of silver thick film, and the bonding strength of the silver thick film on the substrate were studied. The results show that a thick silver film with glass and silver powder content ratio of 1∶9 (wt.%) sintered at 530 ℃ for 10 min has a low resistivity of 2.2 μΩ·cm and a high shear strength of 56.0 MPa at room temperature. Increasing the sintering temperature can effectively promote the flow, wetting and spreading of the glass, the growth of necking between Ag particles, and the growth of Ag particles, thereby improving the solderability of silver thick film significantly. In addition, the nano-scale elemental bismuth produced by the oxidation-reduction reaction of Al, Mg and Bi₂O₃ was detected at the interface of silver thick film and aluminum substrate. It shows that an excellent metallurgical bond was formed between the silver thick film and the aluminum substrate.