Control Equipment

Due to rapid changes in the chemistry of an operating electroless plating bath, frequent analysis and replenishment are required. Hence, automatic control equipment has been of interest (Ref 70) almost since the baths were first commercially employed. A benchmark controller, developed in about 1980, measured and controlled copper, hydroxide, and formaldehyde contents. Copper content was determined by an optical absorbance method, hydroxide and formaldehyde contents by a titration method. Over the years, the simplicity and reliability of such equipment have undergone great improvement, but the basic techniques of analysis have remained essentially the same (Ref 71). Today these control systems are commonplace in all but the very smallest installations and are used to automatically replenish all bath components, as well as for bailout. Recently, to address the added control requirements of full-build electroless copper baths, a new, more accurate method of copper analysis and control has been developed and commercialized. This method is based on vibration of a quartz crystal that acts as a microbalance (Ref 72), thus measuring the mass of copper plated on its surface and providing real-time measurement and control of thickness.

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