Optimised Nitrogen‐based Atmospheres for Copper Thick Film Manufacture: Part 2: A Comparison of the Effects of Different Gaseous Dopants

This paper reports the final results of a development project conducted on nitrogen‐based atmospheres in order to improve the firing of copper thick films. Having shown that improvements in copper thick film performance can be obtained under production conditions by the control and regulation of oxygen additions during the first stages of firing, the authors studied the effects on copper thick film systems of other gaseous oxidisers (CO2, N2O, H2O) injected into the nitrogen furnace atmosphere either throughout the entire furnace or into its burnout zone only. SEM examinations of the microstructures of copper films, correlated with properties such as adhesion, solderability and resistivity, allow ideal firing atmosphere conditions for copper thick film manufacturing to be determined: it is necessary to restrict atmosphere doping to the burnout zone; oxygen and water vapour are the most effective gaseous dopants. Some specific equipments have been developed for controlling the injection of these dopants into the furnace atmosphere.