New Wire Bondable Gold Thick Film Conductors For LTCC Applications

Low temperature co-fired ceramic (LTCC) with silver and gold conductor systems offer a low cost, high performance, and high reliability solution utilizing the advantages of ceramic technology. Gold conductors are generally used in applications requiring best reliability in harsh environmental conditions. Gold conductors are bonded to active or passive components through wirebonding, soldering, or epoxy attachments. A gold conductor for wire bond applications requires good bond strength to the substrate without weakening the wire. Generally, glass, metal oxides, or a combination of these can be used as adhesion additives in thick film conductors. Upon sintering, the adhesion additives interact with substrate to provide adequate adhesion to the substrate. The selection of adhesion additives can significantly alter the surface of the gold conductor and affect the gold wire bond strength. This paper describes the development of new wire bondable gold conductors for LTCC applications using Ferro’s A6 tape. It has been found that there is a tendency for glass in the LTCC substrate and in the gold conductor to migrate to the top of the gold conductor surface. Gold conductors with a glassy surface may display inadequate bond strength for gold wire bonds. Effect of oxide additive on the migration of the glass was studied. It is observed that with a proper selection of oxide additives the migration of glass in the LTCC substrate to the gold surface during firing is prevented and gold conductors with less excessive glass on the surface exhibit excellent wire bond strength. The effects of adhesion additives on blister and shrinkage match of the gold conductor to the A6 dielectric are discussed.