Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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finishing plant engineering CONTINUOUS STRIP PLATING OF ELECTRONIC COMPONENTS BY JOHN G. DONALDSON CONSULTANT, TUSTIN, CALIF. Stamped and preformed electrical contacts attached to a carrying strip, machined or "loose-piece" contacts held by a narrow metal band (bandolier), and solid strip are typical of the materials plated in continuous lengths in specially designed equipment using chemical processes developed for high-speed performance. The entire surface of the strip or parts being processed may be plated, or the deposits may be restricted to small discrete areas using one of several types of selective plating techniques. Two divisions of the electronics industry, connectors and semiconductors, utilize most of the products produced by strip plating; predominately, connector contacts, lead frames, various connecting devices, leads, headers, or the solid strip materials from which contacts and components are subsequently formed. Gold, silver, or tin and tin-lead alloys are the deposits most often specified, usu- ally over barrier coatings of nickel or copper. Other metals also being specified as a coating on electronic devices include palladium, palladium-nickel, tin-nickel, and cadmium. Copper and its alloys, particularly phosphor bronze, brass, beryllium copper, nickel, and nickel-iron alloys (i.e., Kovar and 52 alloy), nickel silver, steel, and stain- less steel are the base metals usually plated. The thickness of these materials will typically be between 0.005 and 0.020 in., although requirements for as low as 0.002 in. or as high as 0.040 in. are not unusual. Strip widths, including the carrier, gen- erally run between approximately 0.5 in. and 3.0 in., but both wider and narrower materials are being processed for particular applications. EQUIPMENT From a strictly mechanical viewpoint, the principle of reel-to-reel plating is deceptively simple. Unreel the unplated material from a feed coil, convey it through a series of processing stations, and re-coil the finished product onto a take-up reel. Due to the shapes, sizes, and fragility of the materials being plated, however, and because of the number of difficult and complex plating requirements specified, continuous reel-to-reel plating is a relatively complex and difficult oper- ation. So much so, in fact, that the equipment must usually be customized to at least some degree for each application. Most strip plating lines are comprised of six main sections: 1. De-reeling. 2. Preplating—including cleaning, etching, and activation. 3. Plating either overall or selective. 4. A postplating section for (a) precious metal recovery, (b) special postplating treatments, if required, and (c) drying. 5. Reeling. 6. Drive, transporting, and contacting system. How each of these is constructed depends on the type and configuration of materials to be processed and the plating requirements. The ability for one line 609

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