Development of a new multilayer copper-dielectric system

The development of a copper conductor and multilayer dielectric ink system, designed to overcome the dielectric porosity, Cu diffusion, and reheat stability problems commonly experienced with thick films fired in nitrogen, is discussed. The characteristics of the Cu and dielectric inks, which are formulated for screen printing on alumina substrates and firing in nitrogen at peak temperatures of 900-925 degrees C, are discussed. The dielectric, which is based on a devitrifying glass with ceramic oxides, produces extremely dense films having thermal expansion characteristics matching the substrate with a reheat stability up to 900 degrees C. Copper thick films on the dielectric are free from blistering in multilayers, and the dielectric is quite resistant to the diffusion of liquid flux phases present during the firing step. The dielectric typically passes the conductive salt solution porosity test with less than 1 mu A/cm/sup 2/ leakage current. The influence of the organic binder-system on dielectric film density and results of dielectric porosity and accelerated aging tests on multilayer circuit boards are discussed.<>