Etching Equipment and Configuration
An expanded discussion of the effects of internal configuration of the etcher is given in the Outerlayer Etching Area.
Both Ammoniacal and the Cupric Chloride etchants are extremely corrosive to all common metals, and consequently the etching chambers are usually made of plastic. Polyvinylchloride is the most common material of construction, Polypropylene is also used. The only metal that is used in etchers today is Titanium.
In order to ease the problem of waste treatment of rinses, many Ammoniacal etchers are set up with a “rinse” chamber filled with etch replenisher solution installed immediately after the etching chamber. This chamber is fed with fresh etch replenisher, on demand, from the etch controller. When the chamber is filled, it overflows into the etch chamber itself. Thus effectively the etch sump is fed from a rinse chamber, rather than adding the replenisher directly into the etching chamber. The net effect of this is that the actual rinse water going to waste treatment contains much less Copper than it would if the rinse water were removing full strength etchant. The rinse waters therefore are theoretically easier to waste treat. The rinsings from the etchers are the largest single source of Copper contamination in the final effluent from the plant, at most PCB manufacturers.