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I see most printed circuit boards are green in color. I’ve seen some blue and yellow boards, but not so many – so I have a question: Why are most PCBs green?
The above question is not only asked by electronics hobbyists but also questioned by engineers, so today let’s unravel the mystery.
In the early days, due to technological restrictions, quality inspections relied on workers manually checking the boards with their bare eyes. Squinting at tiny circuits all days is tiring work, but neurologists and psychologists agree that the wavelength of green light has relaxing effects on the body and can reduce fatigue. Additionally, they have found that the sensors in human eyes, or cones, are most sensitive to green light. Therefore, the contrast is greater between the circuit traces, pads, silkscreen printing and empty spaces. Just by observing the boards from the outside, one can easily identify defects in the outer layers. Compare the below images of green boards to other colors such as blue, yellow or even black and white. With higher contrast, errors are easier to spot.
Solder mask is typically applied using silkscreen techniques. A large blob of oil is dragged across a screen mesh with the circuit board underneath. The circuit board is removed for curing, and the next board goes under the mesh. But hey, hold on, I want another solder mask color. Well, then you have to remove the excess solder mask oil and wash the silkscreen before applying the new color. Otherwise, a silkscreen station is needed for each color. Furthermore, for white or lighter solder mask shades, you’ll also need another station for the black silkscreen ink. The oils also don’t keep for very long. If you find that one color is not particularly popular, the chemicals will be wasted and efficiency will be impaired.
Similarly, some factories will not accept certain combinations of PCB features with colors other than green, since green is by default the most popular color.
One reason is that the solder mask used on PCBs is green. The glass epoxy has a natural green tint to it, and many use this color because it is so commonplace. The color of the board does not affect the efficiency of the board, but it does affect the resolution, which is the precision of the board. While green boards do not make a difference in how devices work, green solder masks do make a difference. The green solder mask dams better than other colors, at 0.1mm, when compared to primary colors that dam at 0.12mm, and black and white which dam at 0.15mm.
Some believe that the green color was chosen and made standard because of the military. The United States military studied PCB colors and found that green was the most effective color, especially when they tested them in adverse situations.
Because of their tests, the military decided that green printed circuit boards would be the norm. And, the pcb manufacturers who supplied circuit boards to the military had several non-military customers, too. Businesses didn’t need to make them in different colors, because most PCBs aren’t seen by anyone other than the manufacturers.
Liquid photoimagible solder mask, or LPISM, comes in multiple colors to match a company’s manufacturing standards, branding or preferences. Depending on the situation and production process, certain colors can work just as well as green or even surpass it. Common alternative colors include:
White: Some companies create white circuit boards for their appearance, especially for show models. The standard white text printing is very difficult to see on a white PCB, but black silkscreen text stands out perfectly.
Black: PCBs in black make it easy to see labeling and large components, but they can also increase heat.
Red: A red PCB offers comparable levels of contrast to green and creates a fresh-looking appearance.
Blue: With one of the highest degrees of contrast with silkscreen, blue PCBs work well for applications involving many labels.
To learn more about the PCB colors you can order from a supplier, contact us immediately.