This paper reports the results of development work conducted on nitrogen‐based atmospheres in order to improve the firing of copper thick film systems through continuous furnaces. The proposed solution is particularly suitable for industrial production conditions since it allows variations of the material quantity processed per unit time, resulting not only in an improvement in quality but also in productivity. Such improvements have been achieved by using a new gas distribution system which provides both zone control and regulation of oxygen additions in the nitrogen furnace atmosphere. An efficient set‐up of this system has become possible thanks to precise control of the oxygen profile in relation to the temperature cycle, taking into account various inks' characterisation, and owing to an extensive study of the effects of oxygen additions on copper thick film properties. The solution was tested in a muffle‐lined belt furnace with several commercial dielectric and copper inks, and for increasing oxygen additions into the furnace preheat zone. Different sample patterns were designed to test both monolayer and multilayer systems. The test programme includes measurements of resistivity, bondability, solderability, dielectric breakdown voltage and adhesion of copper films on alumina and on dielectric layers before and after ageing. Ink characterisation by thermogravimetry and by several gas analyses has confirmed that the organic vehicle removal mechanism under nitrogen atmospheres doped with oxygen is a burnout. Indeed, significant oxygen consumption occurs within the temperature range of the removal, as a function of the amount of ink processed. Oxygen additions in the furnace burnout zone greatly improve both the dielectric breakdown voltage and the adhesion of copper on alumina and on dielectric (especially after ageing), while sheet resistivity, wire bondability and soft solderability are not altered below a defined O2 level. It is therefore possible to determine an optimum oxygen addition range for which the thick films fired under such conditions will have the best characteristics. This optimum oxygen window is achieved thanks to a new regulation system which operates whenever variations occur in the quantity of paste processed.

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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.

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