Software Product Line Economics Revisited and Partial Validation

A sample of copper electroless plating solution, containing complexed cupric ions, is modified to provide a concentration of uncomplexed cupric ions. A pH probe (40) monitors the pH level of the modified sample and feeds a signal to a pH control circuit (42) which selectively adds a diluted acid in order to maintain the pH level of the modified sample at a desired level. Specific ion and reference probes (44 and 46) are positioned in the modified sample where, in the presence of uncomplexed cupric ions, a voltage signal is developed. The voltage signal, which is indicative of the copper concentration of the modified sample, is a measure of the copper concentration in the plating solution. A copper control circuit (48), which is responsive to the developed voltage signal, facilitates the addition of cupric ions to the plating solution to maintain a desired ratio of complexer to copper concentration.