Laser machining and metallization of vias in aluminum nitride

A via metallization technique involving excimer laser ablation of aluminum nitride substrate with a metal backing, attached with cyanoacrylate adhesive was investigated. The objective was to develop a procedure to ensure good electrical interconnection between the thick film conductor pads and the walls of the via. An aluminum nitride compatible Ag-Pd thick film paste was used in this experiment. Two different sequences were tested: In the first sequence both sides of the aluminum nitride substrate were printed and fired and then the vias were laser drilled. In the second sequence, one side of the substrate was printed and fired first, then the vias were laser drilled and the second side was printed and fired. In both of the above sequences, laser ablation of the printed conductor and redeposition of the ablated metal backing are necessary for making a proper contact with the thick film conductor pads.