Metal Finishing Guide Book

2013

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The spine for PCB rack is fabricated out of copper with stainless steel reinforcement or bracing. Some PCB racks are fabricated entirely out of T316 stainless steel. All PCB racks have a top thumb screw, which securely fastens the rack to a work bar, this top thumb screw is stainless steel, plastisol coated, and is bigger than the screw that holds the board. The top thumb screw also is held in place with the added support of a threaded top nut. This threaded top nut is needed to provide additional torque support for the top thumb screw when tightening the rack to the work bar. PCB cleaning can be done in a slotted basket. The basket should have 1/4-in. spacing between slots, be fabricated out of stainless steel, or be plastisol- or Halar-coated steel. Fig. 6 Close up view of Halar is a highly protective coating with high temprinted circuit board perature characteristics, this coating is much more (PCB) tip showing only the expensive than plastisol. stainless steel contact and In the case of very flexible contacts, it is necessary plastisol trimmed away to design racks for each individual operation dependfor a square fit for the PCB ing on parameters that are specific to each PCB opera(two-point contact). tion. Some PCB racks have been designed with adjustable spine or cross members to accommodate different size boards in each production process. PCB racks after a period of time will accumulate plating buildup in the contact area and will need to be repaired to continue to be productive. The PCB racks are repaired by stripping off the metal buildup and plastisol, repairing and cleaning the contact area for corrosion, and fixing the spine. The rack is then plastisol coated and trimmed to customer specifications. The contact area on a PCB rack is a slot with a contact point between the thumb screw and contact point. This slot is a specified width and the outside of the slot can be V-shaped to help with the racking of the board. Electroless Nickel Plating racks designed for electroless nickel can be as simple as using a strand of copper wire to hold the piece to be finished. Stainless steel contacts can also be utilized. Electropolishing Electropolishing racks can be grouped in the category of a rack that needs positive contact, usually a titanium tip, because of the need for chemical resistance. Copper spines are still used and the rack is plastisol coated. Racks should hold the work so that gas pockets will be eliminated. 716

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