Performance of a Robust Lead and Cadmium free Thick Film Gold Conductor that Exhibits High Fired Film Density and Reliable Wire Bond Adhesion

摘要

Thick film gold conductors have demanding performance requirements. The thick film paste manufacturers are expected to produce conductors which are lead and cadmium free with excellent fired film properties that have the same performance and properties as classic cadmium containing formulations. These conductors must have a defect free fired film surface (i.e. defects, pills, agglomerates) after multiple firing steps and must perform well on substrates from different suppliers, as well as a multitude of processing requirements used by Hybrid Circuit Manufacturers. Thick film gold pastes are primarily used in high reliability applications such as medical devices, military applications, and high frequency circuits. As the circuits decrease in size and become more complex, the thick film gold properties become increasingly critical. The challenge is to develop a robust gold conductor formulation which has good performance after multiple firings on substrates from multiple suppliers. Heraeus has been proactive for the past decade in the development of thick film products that are both lead and cadmium free. To date, Heraeus has developed and introduced into the market many environmentally friendly and RoHS compliant thick film products. This paper discusses the experiments that were preformed examining the contribution of gold powder, organic and inorganic system which resulted in a newly developed thick film gold conductor paste for use in a wide variety of applications. Wire bonding data is presented, with both gold and aluminum wire, on top of both 96% Al{sub}2O{sub}3 and dielectric substrates with reliability results. Data will show compatibility between the lead and cadmium free gold conductor and a variety of RoHS compliant solderable conductors to allow for its use in mixed metallurgy circuits.