Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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continuous strip plater. Metal concentrations and solution conductivity are higher than with conventional solutions and higher than normal operating temperatures and solution agitation rates are specified. Because the plating on electrical components imparts critical functional characteristics, much care must be taken to assure that the higher speed process- es produce a satisfactory deposit. Such features as hardness, wearability, bond- ability, and solderability are all significantly affected by the structure of the deposit, the presence of impurities, and by minute differences in the percentages of hardening elements. Obviously, it is important that the solution operating parameters be constantly monitored and closely controlled. Good filtration is necessary and continuous carbon treatment of all plating solutions is advisable. The plating and process- ing cells as well as the reservoir tanks should be covered to avoid airborne and acci- dental contamination. METAL PREPARATION The processes used for pretreating materials being reel-to-reel plated are basi- cally the same as those employed in other types of plating operations; howev- er, since immersion times are very short, varying from approximately 15 to 30 seconds, some modification in make-up may be required and good solution maintenance is critical. To meet the high-quality standards required in components used in elec- tronic devices, excellent and reliable surface preparation is essential. This means that both the processing cells and the preplating solutions must be designed to ensure the complete removal of soils and oxides or surface films. Further, the sys- tems must be so engineered that recontamination of the surfaces is impossible. For example, the air used for wiping must be dry and filtered and the materials being plated must not be allowed to dry between any of the operations being per- formed. The surfaces of most materials being reel-to-reel plated will be contaminated with both organic and inorganic soils. Light duty cutting and rolling oils, plus airborne shop oils are the source of the organics. The inorganic materials exist in the form of light oxides and heat scales, dust and dirt particles, and, occasionally, surfaces lightly corroded due to poor handling and storage. Small surface scratches from the rolling and forming operations are not uncommon and burrs produced during stamping and cutting are usually present to some degree. When the plating is to be nonporous and/or the burrs need to be removed, a polishing (i.e., electropolishing) step must be included in the pre- treatment sequence. When the types of materials to be processed are limited to but a very few, and the type and extent of the soils that must be removed are known, the preplating cycle can be relatively simple. It may consist of only a few operations: 1. Alkaline soak clean. 2. Rinse. 3. Alkaline electroclean. 4. Rinse. 5. Acid activation (deoxidize). 6. Rinse. 7. Plate. Both job shop and captive plating departments may anticipate that the basis 615

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