Improved wetting of gold active braze alloy on diamond for use in medical implants

Medical implants containing active electronics must have a leak-proof encapsulation to be certified as safe for human use. Implantable devices made from diamond demonstrated exceptionally long implantation lifetimes due to the outstanding biostability and biocompatibility of the material. However, since diamond does not melt and is therefore not weldable, forming joints between diamond components or embedding metallic wires and bonding pads within diamond is challenging. One method consists of using active braze alloys to bond diamond surfaces together. These active brazes comprise a precious metal alloy containing a carbide forming element that chemically bonds to the diamond as the braze metal melts. Silver-based active braze alloys are used successfully for brazing diamond in industrial applications, but silver is toxic to living tissue and, therefore unsuitable for use in implants. Gold active braze alloys (Au-ABA) are biocompatible but exhibit very poor wetting on the diamond. Here we demonstrate the use of molybdenum (Mo) and niobium (Nb) interlayers including single layers of Mo, Nb or Mo/Nb bilayer thin films as a solution to improve the wetting of Au-ABA on diamond surfaces. Theses interlayers provide for excellent penetration of the braze into the grooves and crevices in the diamond surfaces. We report on optimum recipes for the interlayer, both for the fabrication of weld lines and for the formation of smaller complex micro-structures and hermetic electrical feedthroughs.