The processing and assembly of printed circuit boards are done in clean surroundings to ensure that the components and the air around them are free from contamination.
Usually, manufacturers have their individual methods, but what you’re going to read is the process being applied in general when it comes to making printed circuit boards.
The first part is unwinding woven glass fiber from a roll and then feeding it through a processing station. The glass fibers will then be infused with epoxy resin. After which, the fibers are passed through rollers and given its desired thickness. Any excess resin will be removed as well, and the finished substrate will be produced.
The substrate will now pass through an oven, semicured, and cut in large pieces. The panels will then be stacked in layers with adhesive-backed copper foil in between. They will now be placed in a press that’s subjected to 1500 psi pressures and 340°F temperature for at least an hour. This process will cure the resin and bond the copper foil tightly to the substrate materials.
Hole Drilling and Plating
The substrate panels will now be stacked one on top of the other and pinned as well to avoid movement. They will be placed inside a CNC machine, and will be drilled holes depending on the pattern during the time when the boards are laid out. The holes’ rough parts will be smoothened out to remove any excess materials that stick to the holes.
The holes’ inside surfaces that are intended to give conductive circuits are now plated with copper. The remaining holes –non-conductive ones—are plugged to avoid them being plated.
The process for the printed circuits’ pattern can either be ‘additive’ or ‘subtractive’.
•Additive – Copper is added or plated on the substrate’s surface in the preferred pattern, and the rest of the surface is left unplated.
•Subtractive – The substrate’s entire surface is first plated, and those areas that aren’t part of the pattern will be etched away.
Attachments, Coatings and Cuts
The substrate’s edge will now be attached to the contact fingers and connected to the printed circuit. The fingers are masked off to isolate them from the other parts of the board and afterwards plated.
Plating is done using three metals: (1) tin-lead, (2) nickel, and (3) gold. You have to note that the tin-lead coating is really porous and oxidized easily. To protect the coating, the panels are given a hot oil bath, which allows the coating to reflow or melt into a glossy surface.
Every panel will then be sealed using epoxy to shield the circuits from damage as the other parts are being attached. Other markings are stenciled to the boards. The panels will then be cut to individual boards, and the boards’ edges are smoothed.
The boards will now go through several machines that place the components to where they should be situated in the circuit. Small components sometimes use a “chip shooter” which shoots or places the parts onto the board. Larger parts, on the other hand, may use robotics for placement. Other components that are irregularly shaped can be manually placed and fused later.
The components are now fused to the circuits. The fusion is done through surface mount technology and by making the boards go through another reflow process; hence, making the solder paste melt and connect the circuits to the components. Any residue from the solder will be removed using solvents or water through the solder used.
The completed printed circuit boards will now be individually packaged inside protective plastic bags and readied for shipping or storage, unless these boards are to be used immediately.Continue reading →