Posttreatment

As Fig. 5 shows, post-treatments for electroless copper vary considerably, depending on the application.

Printed Wiring Boards. For conventional subtractive pattern plated boards, the panels may be treated in an antitarnish solution immediately after electroless copper. Afterward they are rinsed and dried, prior to unracking and going on to the imaging process. Antitarnish solutions are usually mildly acidic solutions, optionally containing a weakly chelating acid salt such as citrate or tartrate. Alternatively, a dilute solution of a specific antitarnish component such as benzotriazole may be used.

An optional pattern plate sequence, which employs very thin (< 0.5 pm) electroless copper, uses a post-treatment step of thin (flash) electrolytic copper, ~5 pm thick, prior to unracking.

For subtractive panel plating processes, electrolytic copper plating is carried out immediately after the electroless copper process. The electroplating may be either in-line (thus necessitating use of a single flight-bar throughout the entire electroless process) or in separate equipment (allowing more flexibility in electroless equipment and racking, but involving additional handling steps).

Decorative Plating-on-Plastic. After electroless copper deposition, the parts are usually treated with an electrolytic copper or nickel strike about 2.5 pm thick. The purpose of this step is to build up the initial thin electroless film so as to facilitate the subsequent buildup. Following the strike, bright acid copper plating is usually carried out to a thickness of 12 to 25pm. Next, depending on the final finish and physical characteristics desired, one to three different electrolytic nickel treatments may be employed, totaling up to ~33 pm thickness. The final finish is usually electrolytic chromium, 0.12 to 0.25 pm thick; however, the final finish may also be brass, gold, silver, or other finishes.

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