Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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research to comply with the demands of the RoHS Directive. The goal was to design new plating systems that meet or exceed the new environmental laws. In most of the new plating systems available today, lead and cadmium were substitut- ed with other non-regulated heavy metals. In an effort to stay one step ahead, MacDermid started a new line of electro- less plating systems that are completely void of any metals except, of course, nick- el. They utilize organic and non-organic compounds to provide the necessary sta- bility and brightening, and their advan- tages and disadvantages have been previously discussed.1 Before embarking on the troubleshooting discussion, it is important to men- tion that the plating tanks and all the necessary auxiliary equipment must be suit- able for electroless plating.2 Figure 2: Pitting due to poor activity of copper alloy (top arrow). This has also produced poor adhesion (bottom arrow). The equipment must be inert, strong, and resistant to acids. Also, the pretreatment should be appropriate for the particular substrate being plated.3 • clean (free of soil*); • active (free of oxide†); and • compatible (free of poison‡). Troubleshooting EN baths has previously been broken down into two different areas.4 The first aspect covers deposit problems—that is, defects seen on the work being plated but not seen in the obvious action of the plating bath. The second: problems actually seen in the plating bath itself. The opinions given in this article are those of the authors. Differences have been commented on where there is a disparity between the two types of processes. But where there is no difference in the troubleshooting between the two different types of chemistry, no statement has been made about the troubleshooting required for the new baths. DEPOSIT PROBLEMS Poor adhesion. The best adhesion involves a true metallurgical bond (metal-to-met- al) between the deposit (incoming metal) and the substrate (base metal). Without good adhesion, the deposit will fail to meet performance expectations. Quantitatively, adhesion is the force required to separate the plated coating *In metal finishing, the term soil covers all matter that may reside on the surface of a part when it enters the plating room. †From an atomic standpoint, surface atoms have fewer neighbors than bulk atoms. When left to their own discretion, surface atoms satisfy their need for neighbors by reacting with atmospheric oxygen to form oxides. Oxides, if not removed, prevent the formation of a solid metallurgical bond. ‡A compatible surface is one that would not contaminate the plating bath. Electroless nickel solutions are sensitive to contamination of certain metals even at trace amounts. Avoid plating directly on the list of metals that follow: zinc, lead, cadmium, tin, bismuth, arsenic, antimony, and alloys containing high proportions of these metals. It is necessary to apply a copper or nickel strike to such alloys to prevent bath contamination 157 The selected cycle must render the surface of the work pieces:

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