Apparatus and method for automatically maintaining an electroless copper

Abstract

Apparatus and a method are disclosed for replenishing an electroless plating bath with those of its components which are consumed during plating operation, in order that the concentration of components be maintained as nearly constant as possible in the working bath. The system involves withdrawing from the bath a small sample stream at fixed rate, and subjecting this automatically to a sequence of analyses. The system is particularly adapted to control of electroless copper solutions comprising copper ion, hydroxide and formaldehyde as the consumable components. Sequential analyses are made of the sample stream for these components using instrumentation to control actuators which introduce replenisher solutions into the plating tank in response to signals generated by the instruments whenever deviation occurs from a pre-set level. Standardized test solutions of known concentration and rate of feed are introduced into the test stream to optomize test conditions during the analyses. Changes in bath composition occurring during normal plating operations thus provide changes in instrument readings which are analogs of the concentration of the respective components and signals produced by such readings serve to activate the respective replenisher solution feed controls.