Why are Circuit Boards Green?

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Apr 23, 2020|Product Innovations and Design, Technological Advancements and Materials

Many people wonder why are circuit boards green? Why don’t they come in other colors more frequently, and what is it about the green that makes a difference? There are a few things to understand about the green color you see on PCBs, and this article will help clear up any confusion you might have about it. 

What Is the Green Part of a Circuit Board?

First, you should understand that the green part you see on the printed circuit board isn’t actually green. It’s covered by a coating of resin called a solder mask, and it’s actually an oil pigment used to protect it. 

The purpose is to keep moisture and dust from the electronics underneath, and what many people don’t realize is that the components underneath are actually a matte yellow color.

If you see a green PCB, that means the board’s copper circuits are protected. Epoxy resins and solder masks protect the board’s fiberglass core and conductive tracks from any mechanical damage or corrosion, insulating and safeguarding these components during the soldering process.

While many solder masks are green, they do come in other colors like black, white, red, and blue. There are more vibrant colors sometimes used as well, but the most common option is green. 

Why Are Circuit Boards Green?

Circuit boards are green to aid in reducing visual fatigue for inspections, the green pigment is stronger than other options, and when you produce in bulk using the same color, it reduces the cost of the PCBs. 

Ergonomics

The first reason goes back to a dated quality inspection process where inspectors would look at the boards and check each circuit for imperfections causing malfunctions of the devices. Although we don’t use that strategy anymore, a lot of the PCB manufacturing processes still exist. 

Neurologists found that sensors in the eyes are most sensitive to green light, which makes it easier for them to identify traces on a green PCB easier than some other colors. Even though no one is using this slow method of quality control, it’s still a primary reason why most circuit boards are green. 

Physical Superiority

If you’re still wondering, “why are printed circuit boards green?” Here’s another reason. Over time research and development agencies have tested different colors and chemical pigments to determine which one offers the best solder mask. Green produces a dam of .1 millimeters while other colors can only get around .12 or .15. 

In reality, no one cares about the color of the circuit board, but they do care about its reliability and superiority, so that’s where the green comes into play. Most of the green color you see comes from Bromine and Chlorine, which are harmful to our health and environment. 

Interestingly, getting rid of the green PCB substrates would create a halogen-free mask. 

Affordability

To apply the mask, they drag a large drop of oil across a screen that contains the circuit board on the underside. They then remove the board and let it cure, and then they’ll place the next board underneath the mesh. 

If they wanted to use a different color, they would have to remove all the extra oil and wash the screen before they could put a new board in and apply the mask again. This process would require another step and likely slow down the production process. 

Otherwise, they’d have to build individual stations for each color, which would require an increased workforce for the same output.

Additionally, these oils don’t stay fresh for long, so if you have a color that isn’t as desirable as another, you’re likely to waste chemicals that would reduce efficiency and create more hazardous material. 

Since green is the most common color, many factories will not even accept different colors since green is the default choice. 

It’s much more effective and affordable for a PCB manufacturer to produce each circuit board using the same color. 

Old Military Requirements

Another reason why circuit boards are green is due to military testing at the National Materials and Procurement Center in Cedar Bluffs Virginia in 1954. 

This green color offered the right contrast with white ink when they tested it under all sorts of conditions, and they found that every other color didn’t have the same effect even with the same testing. As a result, they stuck with it. 

Exposure Rate

A PCB needs to go through an exposure room with yellow light during the fabrication process, and the visuals they get from a green PCB is better than with other colors. During SMT soldering, the PCB needs a tin coating, which requires optical alignment, and the resolution and clarity of the green solder is what provides better recognition for the instruments.

Focus on Unnecessary Factors

It is true that over time manufacturers have tried to shift the attention away from the features that work and make the best product to try and separate themselves from the competition, but it’s not necessary. Adding new features and changing things like color will only produce an insufficient design. 

Having multiple combinations increases waste and cost while raising the chances of both human and machine error, which can lead to costly mistakes. 

Developing a new solder mask oil would require it to adhere properly, act as an insulator, and cure well, while all looking aesthetically pleasing. Most companies are not willing to pay a premium price for something like this, so it isn’t worth it for the manufacturer anyway. 

Conclusion

So, why are most circuit boards green? The simple answer is because they’ve always done it that way, and there isn’t a clear reason to switch. The green solder mask produces the most durable, functional, and affordable option, and until PCB manufacturers find a better alternative, we expect them to stay green. 

For more information about Candor Industries printed circuit boards, check out our website and don’t hesitate to give us a call if you have any questions about anything you’ve read in this article.