Printed Circuit Boards (PCB) are thin plates of electronic components designed to transfer information within self-contained modules as well as communicate with external devices. The Printed Circuit Board was invented and applied in 1936 by Austrian Engineer Paul Esler as part of a radio set. Today, most circuits used in electronic appliances, machines, computers, and mobile phones are made up of PCBs.
Industrial PCB fabrication consists of many steps which follow the strict protocols set by the IPC in relation to assembly, design, and quality control. These protocols set the standard for each manufacturing company, big or small, all around the globe to ensure that the customers will never get a defective product.
After the design process has been accomplished, data is brought inside an isolated fabrication facility with a controlled environment, preventing the raw material from getting damaged. In here, multiple steps are followed in accordance to the standards of the IPC.
PCB fabrication starts using the data generated through Computer-Aided Design (CAD) which is read by Computer-Aided Manufacturing (CAM) software. The CAM processes the raw data from the CAD and after verification and adjustment, the CAM generates data that will later be used by the different machines in the manufacturing process.
Copper sheets are patterned with protective layers through the fabricator’s CAM system using different methods such as silkscreen, photoengraving, and milling depending on the manufacturer. These patterns will protect the parts of the copper that will be kept during the etching process.
The patterned copper board is bathed in a chemical solution of either Ferric Chloride (FeCl) or a mixture of Hydrogen Peroxide (H2O2) and Hydrochloric Acid (HCL). This removes the excess copper and leaves only the desired pattern. Once reduced, layers of fiberglass are added and afterwards, plated in copper. For multiplayer PCB fabrication, the above processes are repeated until the required number of layers is reached.
The plated boards are sent to be cleaned, dried, and drilled with computer-controlled machinery. Vias, or smaller holes that are used to connect board layers are plated during the drilling process. Vias are used to electronically join the layers of copper where the hole passes through. Further cleaning is done to remove any unnecessary dust that may cause the boards to short-circuit when electric charges are applied to them.
Solder masks are applied to the holes in order to protect the copper from natural oxidation and to prevent solders from sticking. On the other hand, solder pads and connections are intentionally left unmasked to allow for an easier time soldering in gold over nickel or tin, achieving conduction along with protection for the underlying copper.
As per the ICP standards for PCB fabrication, a legend is printed on one or both sides of the PCB. It contains the test points, component designators, switch settings, and other vital information helpful in assembling, servicing, and testing the circuit board.
Unpopulated boards, or boards without any components yet such as resistors, capacitors, or inductors, are subjected to a series of tests in order to ensure their quality and functionality. These tests include (1) visual inspection guided by the published guidelines of JEDEC Solid State Technology Association (formerly Joint Electronic Device Engineering Council), (2) analog signature analysis, (3) in-circuit tests where empirical data such as resistance, voltage, and other basic quantities are measured, and (4) functionality tests to see if the PCB could do what it was designed to do.
Packaging and Protection
The accomplished boards are coated with conformal coating to prevent corrosion, current leakage, or electric shorts due to condensation. A more commonly used technique for protection is sputtering the board in a soft plastic bag inside a vacuum chamber. PCBs are sensitive to static electricity and therefore, are sealed inside antistatic bags during transportation.
Those are the key steps of fabrication. While those may still seem complicated, it’s safe to say that many companies have mastered the art of manufacturing PCBs.