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The day before yesterday evening , one of my friends was chatting with me, who worked in the electronics world. And suddenly, he asked me, “Do you ever think why are circuit boards green?” I was so spellbound that I couldn’t answer it immediately.
I just thought that he asked it out of curiosity, and may be he was mistaken to assume that all circuit boards are green.
So, when I was free from my works, I dig deep into the matter and found that indeed most (not all) printed circuit boards, aka, PCBs are green.
As I advanced further into the matter, I also found that the circuit boards are mostly green due to the solder masking. But there’re other factors related as well, which might evoke interest if you are working with the copper coin PCB or multilayer aluminum PCB.
So, we are putting it up for you.
Copper base PCBs are the most demanding and expensive of all the three types of printed circuit boards. It got the name because the circuit board substrate is made of copper. The use of copper makes these circuit boards highly thermally conductive and versatile.
Its less thermal resistance makes it high-demanding in projects where you need significant current carrying capacity. The copper foil used as the substrate typically has a thickness of around 35μm~280μm. Its thermal conductivity is further assured with the use of aluminum oxide and silicon powder.
Copper Coin PCBs are used for various products, such as in: planar transformers, planar transformers, power convertors, and so on.
There are many theories, hypotheses, and myths circulating the question “why PCB color is green?”
But during my dedicated research, I found that the color of the resin used during the solder masking of the boards’ component is responsible for the green appearance of the circuit board. The solder masking is essential to prevent soldering errors and short circuits on the fiberglass core and electric board components. So, it keeps the PCB ready for use in various applications with any risk.
However, many people postulate various theories for the green color of PCBs that includes a 195-‘s USA military requirement as well.
We are going to discuss all these popular theories in the following sections.
PCB color is green for military requirements (as mentioned earlier), reducing eye fatigue and aiding into quality inspections. And we are describing all these in the following parts.
In the early days of PCBs, quality and compliance officers would like to inspect the circuits for any faults in the component and connections. It was necessary since these imperfections might cause malfunctions in the electrical and communication devices.
According to scientific research, human eyes are the most sensitive to green and yellowish color. That’s why even these days, multilayer and flexible PCB manufacturers use the green soldering mask for their circuit boards to aid the quality inspectors to find any faults quickly.
However, this slow method of finding imperfections in PCBs has long been backdated; we consider it the primary and first reason for making the boards green.
Are you still vehemently wondering as to why most of the printed circuit boards are green? If yes, here’s the second and most crucial reason.
In the beginning, due to easiness in quality maintenance, manufacturers focused on the green soldering mask heavily. It resulted in the R&D section invest more time in developing the green soldering mask more than any other colors.
Also, researchers investigated deep into the matter to find which chemical pigmentation and color combination works best for the soldering mask. And guess what who won the researchers’ race?
The green color came out with flying marks even in the research. It was found that green color has a minimal dam of about 0.1mm only, whereas other colors for soldering mask will only get to as close as 0.12-0.15mm.
And that’s where the green color comes into play. You see, that green soldering mask has less faulty imperfections compared to all colors. So, manufacturers prefer using it.
There’s no such color preference or eye-pleasing theories as such.
During the 1954s, the military quality inspection center at Cedar Bluffs Virginia titled, ‘National Materials and Procurement Center,’ inspected the manufactured PCBs for quality for military applications. They found that green color had a better contrast with their widely used white ink for testing the imperfections.
So, many believe that due to such old school military requirements for comfortable and quick testing of their PCBs, manufacturers built the boards with green color. And the legacy has continued till now.
When manufacturer solder masks a piece of PCBs, they draw the boards through oil to check for impurities and allow the board to set and cure. Then, they will bring the next board.
If the manufacturers have to use a different color for boards, they would require different oil screening for each color. It would add up to the overall costing of the boards. And it is detrimental since, over the years, printed circuit board users have built a conception that these boards will be cheap.
During the new fabrication process, the PCBs will pass through the warm yellow lights in the exposure room. When the boards move through the yellow glow, the green color causes better exposure.
Since the green soldering mask offers optimal visual aids, it helps the manufacturers to align the tin coating better with the components. The alignment of the tin coating is crucial since any faults here would damage the entire board.
During the past few decades, some manufacturers have tried to shift their focus from green-colored solder masking to other colors as well. However, it wasn’t well-received by the companies and customers.
So, manufacturers decided on continuing the green soldering to fix the issues once and for all.
Technically speaking, you will also get to see two to three standard colors except for green for printed circuit boards. It includes yellow, golden, or blue.
You will also see boards in deep-sea blue, white, Ferrari red, and matte black colors too.
Well, it is a complicated question to answer. The green color on circuit boards comes from the Bromine or Chlorine used during the soldering process.
And physicians speak that both chemical elements cause harm to human health. So, some manufacturers are putting an ardent and concerned effort to use other materials for the mask soldering of the boards.
We sincerely aspire and ardently hope that you now have a clear idea of why are circuit boards green. The main reason is the soldering mask used for the boards, which is usually green in color. Other major causes include old military requirements, testing easiness, and customer’s requirements as well.
I am Peter Gong. I have been working in PCB and PCBA industry for 15+ years now. I have been a part of the PCB revolution with my dedication to circuit board technologies and creative ideas. I write in FX PCB to impart my knowledge on PCB and PCBA for all circuit board lovers, manufacturers, and users.
