
Why Are Printed Circuit Boards Usually Green? (2017) - cimnine
http://www.seeedstudio.com/blog/2017/07/23/why-are-printed-circuit-boards-are-usually-green-in-colour/
======
greglindahl
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.

~~~
borgel
At work we often try to do a different color for each revision so you can tell
at a glance what's in a given unit. It's definitely saved me a few times!

~~~
starky
We use different solder mask colours to differentiate different product
variants that share a board outline. It is way easier to tell a factory to
install the red board when making a specific product variant than to have them
read a part number off the board.

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ludwigvan
> 1\. Green can relieve visual fatigue and aid in inspections

> 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.

Perhaps an IDE theme with a green background would be similarly helpful for
programmers. Any particular suggestions?

~~~
CoolGuySteve
Human eyes are more sensitive to slight variations in green than other
colours. This is why YUV video often encodes green sharper and why 16bit
colour give 6 bits to green and 5 bits to red/blue. So on a circuit board with
subtle green-on-green variations, it makes sense that they picked green.

But since people have many more rods than cones, black/white contrast is
easier to discern and white uses all the subpixels in your display to maximize
luminance. And speaking of subpixels, subpixel antialiasing effectively
triples your resolution when displaying black/white contrast.

The brain also highlights contours of contrasting black/white. (There's an
evolutionary quirk in our blue-sensing cones that allows you to see
contrasting blue/yellow better than most combinations too but still not as
well as black/white.)

So sharp white on black or black on white are typically better suited to human
vision if you're trying to discern outlines like when reading text.

Black/white also avoids the persistence effects that cones have, where when
you look away from a green image for example, you'll see an inverted magenta
copy of the image for a second or two.

~~~
ludwigvan
Thank you, very well explained.

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ultrasounder
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.

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Eduardo3rd
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&D/economies of scale. I expect we
will see more and more of this in the coming decades across multiple
industries.

Anything else fit this pattern today?

~~~
brianwawok
QWERTY keyboards? Built so mechanical typewriter keys would not hit. Used for
computers.

~~~
jsjohnst
> Built so mechanical typewriter keys would not hit.

Most likely a myth. There’s tons of articles on it, but here’s one to get you
started:

[https://www.smithsonianmag.com/arts-culture/fact-of-
fiction-...](https://www.smithsonianmag.com/arts-culture/fact-of-fiction-the-
legend-of-the-qwerty-keyboard-49863249/)

~~~
stan_rogers
The authors of the paper seem to believe that the object would have been to
slow down the typist (had the jamming hypothesis been correct). The opposite
would have been true. Increase the difference of the angle of approach of
successive hammers, and you decrease the chance of jamming and increase the
speed. I'll admit that the Z-SE ("dot-dot-dot-space-dot" in early American
Morse, with the length of the space/mark mkaing the difference) problem makes
some superficial sense, but then there's a corresponding R-EI ("dot-space-dot-
dot") and others that aren't reflected on the QUERTY keyboard. (The original
Morse code needed far too much space-length discipline, which is why it was
replaced fairly quickly, even in the NIH-heavy USA.)

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jpm_sd
At this point, they're usually green because they're usually green. It'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't stick to the PCB as well!

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peterburkimsher
Pinouts usually use red and black to indicate power and ground [1]. It's
possible to use several colours of solder mask on the same PCB. [2]

What I'd like to see is a developer board targeted at the education market
that uses colours to show the traces.

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 "plug the red wire
into the red pin" instead of "the top right ... no, other top, turn it
around".

[1] Raspberry Pi pinout [https://cdn-
images-1.medium.com/max/1000/1*QlSyHfcfNu4ePpNoN...](https://cdn-
images-1.medium.com/max/1000/1*QlSyHfcfNu4ePpNoNtKcZQ.jpeg)

[2] [https://i2.wp.com/makezine.com/wp-
content/uploads/2009/12/20...](https://i2.wp.com/makezine.com/wp-
content/uploads/2009/12/200912010746.jpg?resize=1200%2C670&strip=all&ssl=1)

~~~
danellis
Almost certainly a lot cheaper to just use keyed connectors.

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bsder
> Green solder mask is physically superior

Possibly chemically. Practically? _EVERY_ other solder mask color is better.

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.)

If I want good soldermask coverage, I always order an alternate color (with
the requisite expense) and almost always get great results.

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userbinator
Note that in the early days of electronics, PCBs did not have soldermask,
because it wasn't necessary:

[https://en.wikipedia.org/wiki/File:IBM_SMS_card_circuit_side...](https://en.wikipedia.org/wiki/File:IBM_SMS_card_circuit_side.agr.jpg)

~~~
setquk
Also lots of boards had transparent solder mask after that (Tektronix did
this) which was great for debugging!

Examples here:
[http://golddredgervideo.com/kc0wox/tek/7504/detailedpictures...](http://golddredgervideo.com/kc0wox/tek/7504/detailedpictures.htm)

Whole scope is a work of art!

~~~
userbinator
Wow, gold everywhere. Even the ICs have gold-plated pins... that's not
something I've seen before.

~~~
jacquesm
They're beautiful. Good luck oxidizing any of that in normal environments,
those scopes will outlast the people that built them. Old computer hardware
used to be just like that, I would buy the boards by the pound in the 70's for
parts. Gorgeous stuff.

~~~
setquk
Annoyingly the IC sockets tend to oxidise if the board doesn’t! I’ve lost
count of the number of them I’ve had to replace in my life.

If it wasn’t for mechanical switches, pots, contacts and some dubious thermal
design I imagine the kit would last for 100 years easy. I have 40-50 year old
stuff on my bench in daily use.

~~~
jacquesm
There are sockets with gold plated turned inner pins, those do not oxidize.
Cost a pretty penny though.

~~~
setquk
Yeah the Tek scopes were made before they came up with them though which is
annoying. I usually replace them with the Harwin gold plated turned pin ones
as I got a massive box off them from eBay for virtually nothing :)

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

~~~
userbinator
I suspect it's a deliberate choice both as a fashion statement and to
discourage repair.

It's interesting to see a similar phenomenon with desktop PC motherboards:
"gamer" or otherwise "enthusiast" boards are often a non-green colour and come
with superfluous design elements (like plastic covers over the actual
components, which sort of remind me of the engine covers on newer cars...),
while both the ultra-cheap prebuilt and ultra-expensive server boards remain
green and free of fluff.

~~~
zrobotics
I blame case windows for this. The last desktop I built, it was a chore
finding a case that didn't look stupid, and I eventually gave up on a normal
motherboard, as anything with a z170 chip set looked like it belonged in a
transformers toy.

And while people definitely geek out over servers, it's nearly all about
specs. After all, why make something that gets hidden away in a rack in a DC
look pretty?

I suspect that is one reason Apple isn't using green mask, since the
connotation for many people is 'cheap'

~~~
userbinator
Ironically enough, case windows were created so people could show off the
components inside, but now they're only showing off the covers on them.

------
Sniffnoy
What this article doesn't answer is, when it talks about the green soldermask
being physically superior, is that _only_ because it's had more R&D put into
it due to being popular, or would it actually be the best regardless?
(Admittedly, I don'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't even _ask_ the question.)

~~~
hwillis
Solder dams come down to a bunch of factors, but the bottom line is basically
the best dye is the one that lets the resin cure stable and strong.

For instance, white dyes are hard (for a lot of things) because white dye
particles are large[1] and you need a lot of them. That means they can
interfere with curing.

Green dye can be relatively small amounts since green is so visible to the
human eye, but afaik its more down to the fact that theyve been able to tune
the dyes down better over time.

[1]: also why you can't dye anodized aluminum white. Most dyes are colored at
the molecular level, and are much smaller than the wavelengths they reflect.
White dyes need to reflect every wavelength, and normal molecules only reflect
quite narrow ranges where they resonate.

In order to reflect white light you need particles at minimum the size of the
wavelength. Then you need a range of particles for each wavelength. In
practice this judt gives you black, since each particle will also be absorbing
light at other wavelengths. You need one size of particle with fine, often
fractal-like microstructure that has features at every size. That means white
dye particles are hundreds of times larger than colored dyes.

~~~
jacquesm
Thank you. That answers a question I once had but could not get a satisfying
answer to other than 'can't be done'.

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lambda
I love that OSH Park ([https://oshpark.com/](https://oshpark.com/)) uses
purple soldermask. It'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.

~~~
setquk
Actually OSHpark boards I find are pretty crap. They have mouse bites left
over, the mask is crap and the registration poor on some boards. Getting
better boards from JLC but you lose HASL and purple.

~~~
lambda
Yeah, there are a lot more options for easy, small-batch prototyping PCBs
these days. OSH Park was one of the first that was really easy and accessible
to hobbyists, so even if it's not the best or the cheapest any more, the
purple soldermask still has a place in my heart.

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dboreham
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.

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bluedino
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'm not
100% sure.

~~~
SmellyGeekBoy
I have a GeForce 2 which is red, I think it's the earliest non-green card in
my collection (2000-ish).

~~~
wenc
All Gravis Ultrasound cards were red (>1992ish). [1]

It was partly a marketing choice, to make them stand out from conventional
Sound Blaster cards.

[1]
[https://en.wikipedia.org/wiki/Gravis_Ultrasound#Versions](https://en.wikipedia.org/wiki/Gravis_Ultrasound#Versions)

~~~
mhd
Yes, that's the first non-green PCB I can remember, too.

And it took a while until I saw it become common -- I guess a big incentive
was the appearance of side windows on PC cases. At first all DIY (Dremel),
then commercially sold.

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Andre607
The article mentions that there are "even mixed color boards", does anyone
have a photo of any? I did a cursory search and didn't see any, but am
interested in how these looked.

~~~
guan
I recall reading that the map of Italy on the back of an Arduino Uno is
tendered using white solder mask, because traditional silk screens did not
provide enough resolution.

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MrXOR
Soldermask is most commonly green in color but nearly any color is possible

Another reasons: based on old military requirements and standard, UV (ultra-
violet) sensitive photopolymers and LPISM technology patent story

[https://electronics.stackexchange.com/questions/82669/why-
ar...](https://electronics.stackexchange.com/questions/82669/why-are-
circuitboards-traditionally-green)

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

