How Are Printed Circuit Boards Constructed?
Printed Circuit Boards
A printed circuit board (PCB) is a piece of hardboard with lines, pads and other features that are used to connect and power electronic components. It also allows signals to be routed between physical devices. PCBs are made of different materials that are laminated together with heat and adhesive. The substrate material is most commonly fiberglass or a composite epoxy, and the conducting material is copper, which is either plated or etched onto one or both sides of the substrate to form the desired circuit pattern. The copper is then coated with tin-lead to prevent oxidation and provide good conductivity. The contact fingers on the outer edges are also plated with tin-lead and other materials, such as nickel and gold, to increase conductivity.
Before the printed circuit board assembly, it must be drilled to accommodate the metal leads from each component. The holes are then filled with solder paste, which is then deposited using a stencil that is precision registered on the surface of the PCB. A stainless-steel stencil is manufactured with openings that match the pad locations on the PCB, and a machine applies the paste using a squeegee to deposit it over each pad.
Depending on the design, the copper traces and pads may be plated by an “additive” process or by a “subtractive” process. In an additive process, all of the surface of the substrate is plated and then etched to leave the desired copper pattern. In a subtractive process, the copper is first etched away from the substrate and then plated.
How Are Printed Circuit Boards Constructed?
Once the PCB is ready for assembly, it must be cleared of flux residue and inspected for solder quality. The inspection usually consists of visual and mechanical tests, and the defects are recorded in an inspection report. These reports can be used by the manufacturer to improve future production runs and to determine whether a product is eligible for return due to defects or manufacturing issues.
The next step in the PCB assembly process involves connecting the individual components to the circuit board through a soldering iron. The bare board is then passed through an oven or hot oil bath, which causes the tin-lead coating to melt and form a solid bond with the copper. The finished product is then packaged and shipped.
When ordering a printed circuit boad from an online company, it is important to make sure that the design meets the manufacturer’s guidelines. This is called a Design for Manufacture (DFM) check and can be performed by Altest, which reviews the client’s design to verify its feasibility, including part spacing, pin indications, footprint corroboration and BOM verification. This can help to ensure that the final product will work as intended and minimizes risk and cost. A DFM check is a good way to catch errors early in the process, so that the project can be completed on time and within budget. This also helps to avoid costly delays or expensive RMAs later on.