Printed Circuit Board and Assembly
A printed circuit board, or PCB, is an essential component in electronic devices. The conductive pathways engraved in the laminated copper sheets of a PCB support and connect the electronics components to create an operational device. While the terms PCB and PCBA are often used interchangeably, they are not the same: a PCB with components installed is a populated printed circuit board and assembly (PCBA).
The first step in the fabrication process is called panelization. This involves grouping several different printed circuit boards together for processing as one unit. A single panel may have a design duplicated n-times, and the outer tooling strip often includes a set of panel fiducials, test coupons, and hatched copper pour patterns for even copper distribution. Panels can also be etched with specific shapes to accommodate the placement of the components.
After the panels have been properly grouped, engineers use the data from the Gerber files to control how each individual board will be cut and separated. This is done by directing a machine that cuts a pattern along the edge of the board into the desired shape, usually using a v-groove. A second machine, called a depaneling machine, then separates the individual PCBs from each other.
Once the bare copper surfaces of the PCBs have been cleaned, they get coated with solder mask film. This material covers the copper to protect it from corrosion and oxidation during the manufacturing processes. Then, technicians print a legend on the PCBs with information useful for assembling, testing, and servicing the devices they are made in. The earliest method for this was silkscreen printing, which gave rise to the alternative name of “silk screen.” Liquid photo imaging and ink jet are more accurate methods that are increasingly being utilized.
How Printed Circuit Board and Assembly Are Constructed
Depending on the type of product, printed circuit boards can be constructed using either through-hole or surface mount technology. Through-hole construction is the older, more common method. Here, component leads are inserted into holes that line up with the conductive pads or lands on the PCB’s surfaces; the hole holds them in place while solder paste is applied to them and then melted to form the electrical connections.
Surface mount technology is a more recent advancement. In this assembly method, the component pins line up with conductive pads or lands on the surface of the PCB. The pins are then positioned, and solder paste is used to hold them in place temporarily until they are melted to make the connection with the copper. This technique allows for much faster assembly and reduces the number of connections.
After assembly, the populated printed circuit boards are ready to be shipped. They may go through conformal coating, IC programming and functional testing to add value to them before they are shipped to customers.
To ensure the highest quality, the fabricated PCBs must then undergo automated optical inspection. This is a crucial quality check that ensures the layers of the PCBs meet the precise specifications of the engineering drawings. It is a midway point in the production process that helps prevent defective boards from continuing further down the assembly line. Specifically, the AOI ensures that no extra copper was added during etching, and that there are no short circuits or other errors in the board’s design.