Regulations in the electronics industry have called for the elimination of hazardous substances in thick film pastes for quite some time, but exemptions are in place for critical applications. These exemptions are expected to expire in the next few years.
Therefore Heraeus Electronics has developed a new thick film gold conductor paste that can be used for high-reliability applications such as medical devices as well as high-frequency circuits for communications. Those applications require high performance at high and low temperatures, in chemically aggressive environments, or extremely humid conditions. Due to the company the paste performs well on dielectrics and on oxide substrate compositions even when multiple firing steps are required.
For the paste specially matched ingredients are used. First, the specific gold powder ensures a higher and tighter bond distribution. Second, a new vehicle formation that ensures maximum densification. Third, a special material combination achieves good bond strength when etched on aluminum oxide.
The new thick film paste from Heraeus Electronics can screen print and resolve fine features down to 100 micron-size lines and spaces. The paste also can be etched using methods like photolithography processes. This results in even higher density circuit designs down to 25 to 50 micron-size lines and spaces. Wirebond adhesion of both thin gold and aluminum wire is sufficiently good when fired directly onto ceramic as well as on dielectrics.