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Keywords
Electroplating, Copper, Printed circuit boards
Abstract
Despite the fact that insoluble anodes are becoming more utilized in acid copper electroplating for printed circuit board manufacture, little work has been published on the impact of using such anodes on the process control of the baths or their effect on the electroplated deposit. In this study, two electroplating tanks were set up, which were identical in all aspects except that one tank used the traditional phosphorized soluble anodes, whilst the other employed insoluble anodes. Incorporating insoluble anodes into the electroplating tank caused a large increase in brightener consumption rate and the mechanical properties of the electroplate and the throwing power tended to be somewhat inferior when soluble copper anodes were employed. This was thought to be due to the problems of controlling the brightener concentration at optimum levels rather than to any deterioration in the electrolyte, attributable to, for example, by-product build-up.
Introduction
Acid copper electroplating has traditionally utilized soluble copper anodes but, with the onset of high current density horizontal processing techniques, these anodes have been found to have considerable drawbacks. Indeed, the incorporation of insoluble anodes into the high speed electroplating equipment has become critical to the viability of such machines, since they, can operate at high anode current densities, allow excellent solution flow both at the anode and cathode and are virtually maintenance-free (a more detailed comparison of the two types of anodes has been reported previously (Cobley and Gabe, 2001; Cobley et al., 2001)). Although the use of insoluble anodes for acid copper electroplating is still relatively uncommon, those companies that employ such anodes have reported dramatic increases in brightener consumption. Despite this, there has been no published laboratory work to determine the extent of this occurrence. In addition, it was not known whether this phenomenon would actually have any detrimental effect on bath life or the quality of the electroplated copper.
This paper details a "life study" that was performed to compare an acid copper-plating bath incorporating insoluble anodes, with the one that used the traditional phosphorized copper anodes. The brightener consumption rates and the physical properties of the electrodeposited copper were monitored along with other process parameters.
Experimental
Plating tanks
Two tanks of 3201 volume that...