What You Need to Know about PCB Fabrication

Printed circuit board or PCB is a board that contains layers of pads and lines that electrically connect points together. The main function of a PCB is to allow power to be routed between physical devices. The metal that allows electrical connections between the PCB surface and the components is solder. In terms of composition, a PCB has different, alternating layers that have different materials. Using heat and adhesive, they are all laminated together. In simple terms, think of it as lasagna or layer cake. There are several important processes involved in manufacturing PCBs. One of the most important processes is PCB fabrication.

In order to truly understand PCB fabrication, one has to go through the entire PCB manufacturing process.  This starts with the PCB design. There is no standard printed circuit board. Each board possesses a unique design and function for a particular product. The board must be designed in order to perform a specific function for the space allotted. This is called PCB fabrication drawing. The fabrication drawing has to show the dimensions of the board and the tool hole. Aside from that, it also has to show a graphic representation for each hole on the board. This drawing is very important because it will be used by the board manufacturer in addition to the data files to test and check if the PCB is made according to specifications during the post-processing phase.

There is software available that’s used to layout the design or circuit pattern. The design and location of the holes for component leads will be laid out on the board, and the spaces are very small, around 0.04 inches or smaller. The information will be translated into instructions for a controlled drilling machine or a solder machine. When the circuit pattern is laid out, a negative image is printed out on a clear plastic sheet. Copper is the material that is used in the printed circuits. They are usually plated or etched on the surface of the substrate.  The printed circuit pattern is created using either the additive or subtractive method. In the additive method, copper is plated into the surface of the substrate in the specific pattern, while the rest of the surface remains un-plated. In the subtractive process on the other hand, the whole surface of the substrate is plated, then the areas that are not part of the pattern are etched away.

PCBThe substrate is usually made from woven glass fiber impregnated with epoxy resin. To prevent oxidation, the copper circuits are coated with a layer of tin and lead. They are then plated with tin-lead, then nickel and finally, gold, because it is an excellent conductor of electricity. The tin-lead coating is then fused. The panels are sealed using epoxy. This is done to protect the circuits from being damaged while the different components are being attached. The panels are then cut into boards.  The components are mounted either by manual soldering or using surface mount technology.

During the PCB fabrication process, a strict quality control process is done. The process includes both electrical and visual inspection. This is made in order to detect flaws, usually by human error or generated by machines. Human error could be the application of excess solder paste or heating the solder quickly. Machine error could be components that are misplaced on the board or shifted before soldering. Testing completed boards is also part of the process. This is done to ensure that their output is within the desired limits and that they are performing well. Finished boards also go through environmental tests under extreme impact, heat and humidity. Some manufacturers even go the extra mile and monitor the output by investigating the detected failures. These tests ensure that the PCB fabrication process adhere to strict quality standards.

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