Whether you’re a professional electronics designer or a hobbyist, high-quality custom-printed circuit boards (PCBs) can be had within a week of ordering—even faster, in some cases. These PCBs are available at prices low enough that you may question how it’s possible for them to be made. The answer, in large part, is due to the heavily automated smart factory concepts used in production, starting with the ordering process itself.
Once you design your circuit board using electronic design automation (EDA) software such as KiCad, Eagle, or Altium, the automated PCB manufacturing process continues at the PCB fabricator, often referred to simply as a “fab.” You (virtually) plot out a standard set of instructions—typically Gerber files in the RS-274X or RS-274X2 format—along with the drill files. These are then uploaded to your PCB manufacturer of choice. Many vendors, such as OSHPark and PCBWay, will give you an instant quote that you can use to order your board.
Manufacturers typically check the uploaded boards to make sure that their design rules are not violated, so that the PCB can be properly made. This involves significant automation, but some human intervention and/or back-and-forth may be needed. Once checks and communication are finished, multiple customer boards are combined onto a single to-be-cut panel. Typically, these panels are cut to a standard size for a fab’s process, with copper outer layers, and an inner FR4 (fiberglass) substrate to provide strength and insulation.
Elements of the Automated PCB Manufacturing Process
While it would be impossible to describe the intricacies of how all PCB manufacturers do things here, we can break the automated PCB manufacturing process down into several primary elements. Note that we’ll be considering two-layer board manufacturing for simplicity, but many more layers can be used as needed via a stacking and bonding process. Also, while this smart manufacturing process involves a massive amount of automation, humans are still needed for tasks like transporting work-in-progress, machine setup, and final checks.
1. Drill Via and Through Holes
Typically, the first step in the PCB fabrication process (after cleaning and deburring operations) is drilling for through-hole components and vias. This is performed in a drill machine, which can form holes down to 100 microns, smaller than a human hair (which is roughly 150 microns in diameter). Bit changes for different diameters are performed automatically.
2. Photo Plotting and Layer Resist
In order to form PCB traces and copper fill areas, a negative image of the finished copper is printed on a transparent sheet, based on the supplied Gerber information. The panel is coated with a layer of photosensitive film on both sides, known as photoresist. The printed sheet is aligned with the panel’s top and bottom, and UV lamps harden the photoresist in areas where there is no image printed on the film. Further processing washes away the unhardened photoresist, along with the copper underneath.
At this point, the board is still part of an entire panel, which may contain a number of designs. Cleaning is performed at many points during the overall PCB manufacturing operation, and different inspections, including optical processes, are performed progressively in order to deal with errors as early as possible.
3. Plating and Chemical Processes
Additional copper is electroplated onto the PCBs, creating a conductive channel for vias and through hole connections, and building up the original foil. Different thicknesses of copper plating can be specified, and the whole process is carefully controlled to meet customer requirements.
4. Solder Mask, Silk Screen, HASL
Solder mask, which protects the copper traces, is applied as a liquid to both sides of a PCB. After this is applied, the boards are baked to a semi-hardened state and a transparent printed sheet is then applied to both sides. The exposed solder mask is hardened with a UV process, and the unexposed solder mask is removed, similar to the photoresist process performed earlier.
An inkjet printer then applies a visible layer known as the silkscreen, used for component identification and other marking purposes. Finally, a process such as hot air solder leveling (HASL) is typically performed to protect exposed solder pads from oxidation. A flying lead probe inspection can then be performed to ensure the PCB conducts and resists current flow as designed.
5. Profiling and Routing
With each PCB on a panel properly processed and checked, a computer-controlled routing operation cuts the profile and non-through hole internal features of the board. These edges and features do not need to be straight. Panels can also be v-scored (partially cut in a “v”) prior to this process. V-scores are restricted to straight lines and allow customers to break apart modules once received.
6. Finish, Pack, Ship
After a final cleaning, further processing to remove artifacts from routing, and inspection, PCBs can then be packed and shipped to customers. It’s an amazing process to get to this point.
PCBs: Process and Fulfillment Optimization
While impressive, note that the process outlined here is a simplification, and that these operations vary between manufacturers and even products. Beyond automation, factor in geographic arbitrage, geopolitics, shipping, and a number of other factors to get a full picture of how it’s possible to produce quick-turn PCBs at an affordable price.
At the same time, printed circuit boards have been in widespread use for many decades, giving the manufacturing process time to mature. Incremental improvements year after year often compound to incredible results. Consider that the next time you order a number of high-quality PCBs at a low price for quick delivery. As for where you get high-quality parts to put on said PCBs, Arrow has a huge inventory ready to ship!
