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Printed circuit boards are assembled in a very clean environment where the air and components can be kept free of contamination. While most manufacturers have their own way of doing things, the following steps may serve as a standard guide to manufacturing a two-sided printed circuit board. The first step is to make the substrate, which consists of woven glass fiber being fed through a process station where it is filled with epoxy resin. The glass fiber is then passed through rollers, creating the desired thickness for the finished substrate and also to remove any extra resin. The substrate material gets semi-cured in an oven, and then is cut into large panels. These panels are then stacked in layers, alternating with layers of adhesive-backed copper foil. These layers are pressed together under 1500 psi in about 340°F for over an hour, fully cursing the resin and tightly bonding the copper foil to the surface of the substrate material. The next step is to drill and plate the holes of our new substrate panels. Special equipment enables manufacturers to drill the holes of several printed circuit boards at one time. The inside of each hole is plated with copper to allow a conductive circuit to run from one side of the board to the other. Next, the printed circuit board requires a pattern on the substrate, which can be created by an “additive” process or a “subtractive” process. In the additive process, copper is plated, or added, onto the surface of the substrate in the desired pattern, leaving the rest of the surface unplated. In the subtractive process, the entire surface of the substrate is first plated, and then the areas that are not part of the desired pattern are etched away, or subtracted. Using tin-lead, nickel and then gold, the contact fingers are attached to the end of the substrate to connect with the printed circuit. The tin-lead material is porous and easily oxidized, so it needs to be protected by passing through a “reflow” oven or hot oil bath which causes the tin-lead to melt into a shiny surface. Each panel is sealed with epoxy to protect the circuits from being damaged while components like instructions and other markings are being stenciled onto the boards. The panels are then cut into individual printed circuit boards and the edges are smoothed. Electronic components are put in their proper place on the printed circuit board while passing through several machines. The largest components are placed and soldered by hand. Medium sized components can be placed robotically. And the smallest components are mounted using a “chip shooter” which rapidly places, or shoots, the components onto the board. The last step to manufacturing printed circuit boards is to package them individually in protective plastic bags for storage and shipping.
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