A Study of Various Nitrogen‐based Furnace Atmospheres and Their Effects on Copper Thick‐film Conductors and Dielectrics

Manufacturers of multilayer copper thick‐film circuitry face the challenge of firing parts in an inert nitrogen atmosphere to prevent the copper from oxidising. Nitrogen, while protecting the copper from oxidation, offers no efficient mechanism for removing the carbon‐based vehicles used in the copper thick‐film paste. Because of this, carbon residues or soot often deposit on the parts during the firing process. In an attempt to improve the nitrogen furnace atmosphere's ability to remove the vehicles, several gases or gas blends were added to a nitrogen‐based furnace atmosphere. Thick‐film copper conductors and dielectric test pieces were then processed using the various gas blends. The physical properties of adhesion, aged adhesion, solderability, and conductivity of the copper conductor test pieces were studied along with the dielectric properties of dissipation factor, insulation resistance, and dielectric constant. Some of the gases tested included H2, H2O, CO, CO2, and a variety of other gas combinations. Test results demonstrated the atmosphere's ability to effect changes in the physical properties of the parts being processed. A proprietary gas blend was developed which proved effective in removing carbon residues while maintaining the desirable physical properties of the thick films. This work demonstrates the ability of certain gas additives to improve the performance of conventional nitrogen atmospheres when firing copper thick‐film circuitry. With the proper selection of the gas additive, atmosphere flows can be reduced, carbon residues eliminated, and the physical properties of the copper conductors and dielectrics maintained or improved.