Why Are Printed Circuit Boards Usually Green? (2017)

One of my startups was purchased by QLogic, which made PCI cards in bulk. One of their corporate standards is that prototypes have red PCBs, to prevent them ever being mixed together with production parts. These days I have some friends who have a particular debit card that's the same color of red. Every time I see it, I twitch.

&gt; 1. Green can relieve visual fatigue and aid in inspections<p>&gt; 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.<p>Perhaps an IDE theme with a green background would be similarly helpful for programmers. Any particular suggestions?

In various places I have worked we used Red color soldermask to indicate that the PCBAs were in early prototype stages(EVTs,DVTs) and once the final designs were released for manufacture(PVT) they were Green in color. This also was used to indicate that these boards were RoHS compliant. Again, this might have been very industry specific(Medical devices in my case) and YMMV. IN another FAANG place that I worked our ODMs who also worked with Chinese Fab houses started out with Green soldermask. Nowadays I find it fascianting that one can order preactically any solder mask color one chooses to, though i have a special affinity towards pink.

Interesting example of a place where a small but meaningful advantage in a manual application (reduced eye strain during visual inspection) leads to a larger, nearly insurmountable advantage in a world where the task has been largely automated thanks to preexisting R&amp;D&#x2F;economies of scale. I expect we will see more and more of this in the coming decades across multiple industries.<p>Anything else fit this pattern today?

At this point, they&#x27;re usually green because they&#x27;re usually green. It&#x27;s the most common mask color, therefore the cheapest. Also, oddly enough, not only do different mask colors have different achievable resolutions (minimum line widths) - some colors don&#x27;t stick to the PCB as well!

Pinouts usually use red and black to indicate power and ground [1]. It&#x27;s possible to use several colours of solder mask on the same PCB. [2]<p>What I&#x27;d like to see is a developer board targeted at the education market that uses colours to show the traces.<p>I think that at least showing the power and ground could reduce the risk of shortouts. It would be a lot easier for teachers to say &quot;plug the red wire into the red pin&quot; instead of &quot;the top right ... no, other top, turn it around&quot;.<p>[1] Raspberry Pi pinout <a href="https:&#x2F;&#x2F;cdn-images-1.medium.com&#x2F;max&#x2F;1000&#x2F;1*QlSyHfcfNu4ePpNoNtKcZQ.jpeg" rel="nofollow">https:&#x2F;&#x2F;cdn-images-1.medium.com&#x2F;max&#x2F;1000&#x2F;1*QlSyHfcfNu4ePpNoN...</a><p>[2] <a href="https:&#x2F;&#x2F;i2.wp.com&#x2F;makezine.com&#x2F;wp-content&#x2F;uploads&#x2F;2009&#x2F;12&#x2F;200912010746.jpg?resize=1200%2C670&amp;strip=all&amp;ssl=1" rel="nofollow">https:&#x2F;&#x2F;i2.wp.com&#x2F;makezine.com&#x2F;wp-content&#x2F;uploads&#x2F;2009&#x2F;12&#x2F;20...</a>

&gt; Green solder mask is physically superior<p>Possibly chemically. Practically? <i>EVERY</i> other solder mask color is better.<p>I find that because green is the default, cheap, PCB soldermask, manufacturers thin it to hell and back in order to save money. As such, I regularly get coverage gaps over vias underneath QFN components which then short to the pad underneath the chip. (Manufacturing tip: if you can, only put vias underneath the chip that are tied to the same signal as the QFN thermal pad and your reliability will be much better.)<p>If I want good soldermask coverage, I always order an alternate color (with the requisite expense) and almost always get great results.

Note that in the early days of electronics, PCBs did not have soldermask, because it wasn&#x27;t necessary:<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;File:IBM_SMS_card_circuit_side.agr.jpg" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;File:IBM_SMS_card_circuit_side...</a>

Apple PCBs are all black nowadays. They probably went all they to make the black pigmened oil as good as green.

What this article doesn&#x27;t answer is, when it talks about the green soldermask being physically superior, is that <i>only</i> because it&#x27;s had more R&amp;D put into it due to being popular, or would it actually be the best regardless? (Admittedly, I don&#x27;t know how one would possibly answer that question without, like, actually trying to invent better soldermask of other colors. But it bugs me that the article doesn&#x27;t even <i>ask</i> the question.)

I love that OSH Park (<a href="https:&#x2F;&#x2F;oshpark.com&#x2F;" rel="nofollow">https:&#x2F;&#x2F;oshpark.com&#x2F;</a>) uses purple soldermask. It&#x27;s a fairly unusual soldermask color, but they use only purple. It looks great with gold plating, and it gives a satisfying sense of branding to for open source hardware and prototyping.

Nit, but I doubt silk screen mask is used much these days. When I was last involved with board production 20+ years ago all our vendors switched to photoimagable mask in order to get the registration accuracy and resolution necessary for fine lead SMT.

Somewhere in the early 3D video card years, I took one out of the box and the PCB was red! Blew my mind. I want to say it was a Diamond card but I&#x27;m not 100% sure.

The article mentions that there are &quot;even mixed color boards&quot;, does anyone have a photo of any? I did a cursory search and didn&#x27;t see any, but am interested in how these looked.

Soldermask is most commonly green in color but nearly any color is possible<p>Another reasons: based on old military requirements and standard, UV (ultra-violet) sensitive photopolymers and LPISM technology patent story<p><a href="https:&#x2F;&#x2F;electronics.stackexchange.com&#x2F;questions&#x2F;82669&#x2F;why-are-circuitboards-traditionally-green" rel="nofollow">https:&#x2F;&#x2F;electronics.stackexchange.com&#x2F;questions&#x2F;82669&#x2F;why-ar...</a>

I have read somewhere else the US Army standarized on it.