Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 615 of 707

Using specially shaped and shielded anodes placed very close to the workpiece in the area where plating is desired. Although these techniques are effective, for reasons both economic and technical, they are seldom used when high vol- umes of components are being produced. Fig. 6. Selective brush plating. (U.S. Patents 4,064,019 and 4,078,982) HIGH-SPEED PROCESSES To produce the great numbers of components required by the electronics industry, it is nec- essary to operate the equip- ment at speeds of at least 10 to 50 or more feet per minute (fpm). Thus, a fraction of the time normally desired for preplating and plating operations is allowed. For example, when run- ning at 25 fpm, the material remains in a 5-ft processing cell only 12 seconds, allowing little time for cleaning, activation, etching, or plating. Because each component, or each millimeter of strip being plated, is subject- ed to exactly the same conditions in a processing cell as all others, the extended treatment times required for bulk plating are not necessary. Nevertheless, the very short immersion times possible made it mandatory that, along with the devel- opment of continuous strip plating equipment, the effectiveness of the solutions had to be improved, either through adaptations in chemistry, changes in oper- ating conditions, or by employing such assists as ultrasonics and pulsed current. Some of the mechanics used to improve solution effectiveness are: 1. High solution flow rate. 2. Direct solution impingement. 3. High-velocity spray. 4. Increased solution temperature. 5. Increased chemical concentrations. 6. Close anode placement. 7. High solution agitation (stirring, ultrasonics, vibrators). Fig. 7. Brush belt plater. 614 HIGH-SPEED PLATING High-speed plating is the term used to describe solutions with greater than traditional deposi- tion rates because of increased solution efficiency and higher limiting current densities. Most plating process supply firms mar- ket high-speed plating solutions tailored to meet the needs of the

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