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A question so simple I've never thought about it before. Usually I get my PCBs made in standard green, but have been offered a blue for my next revision of an existing (green) board at no extra cost.
What colors are available as standard, and why should you choose one over another. Is there a "best" color?
Would any of this affect color blind tech people who work on the board?
As said by others, the color is the result of the solder mask used.
However, it's definitely not true that color is the only difference. For example, Paul Stoffregen of Teensy fame found that a black solder mask had reduced resolution than a green solder mask, and this directly led to lower reliability of black boards.
The color comes from the soldermask, so what you're really asking is what colors of soldermask are available. The answer is that you can get just about any color soldermask, but the less common ones may cost more depending on your manufacturer. Different manufacturers offer different standards. One manufacturer may only offer green as standard and you'll need to pay a premium for blue, red, etc.
To answer your main question about what is commonly available, I have seen green, blue, purple, red, black, and white. Those seem to be the most popular. At work we use green boards to indicate leaded assemblies (because in the past, prior to RoHS restrictions, all of our boards were done in green), blue to indicate RoHS-compliance, and red for prototypes. There is no "best color", it is completely up to you. Personally I don't care for black soldermask or white soldermask because it is difficult to see the traces which could be useful for troubleshooting.
no-color (I mean, transparent) available?
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Aug 30, 2017 at 16:14
It's just paint so various colours are available. Okay, it's a special kind of paint so you may get worse specs on not green colour as that's by far most common one. Specs meaning the smallest bridge and clearances.
I've made black and white boards, LED backlights are white for obvious reasons. If you just take regular white colour solder resist, you're liable to end up with pink as the copper will show through. Red is also seen from time to time.
Black PCB with gold (ENIG) treating looks cool but it's harder to see the traces than on green PCB.
Usually I spec on my PCBs "Black if no extra cost"
An additional "why" ... when possible, I also like to use soldermask colors to denote prototype/test PCBs vs. production. I may have a red or purple (OSHPark) prototype board to test functionality and then move to green for production. I find it helpful when showing photos of a test setup in a work instruction or test report as someone can tell at a glance why flavor of hardware I was using.
I've also used soldermask colors to denote board revisions in a similar manner so that quality inspection or manufacturing doesn't get confused, especially contract manufacturers who may have multiple revisions in the warehouse. Somewhat of a last line of defense just in case.
The colour of commercial PCBs comes from the soldermask. Typically the soldermask "ink" is laid down onto the board using a screen-printer, then the ink is cured and finally a photoimaging process is used to make the gaps.
The soldermask "ink" comes in a variety of colours and custom colours can be mixed. The trouble is to change colour requires cleaning the screen printing equipment which wastes a bunch of time and ink. So muost vendors will have a limited list of standard colours which they produce in enough volume to make it worthwhile keeping a screen printer set up for them.
Note that some colours are more transparent than others. White and black soldermasks in particular tend to make it much harder to see the tracks under the soldermask. Depending on your goals you may see that as an advantage or a disadvantage.
Each manufacturer will have standard colors- sometimes you can even specify matte finish for some colors. Eg. matte black or green. Most common colors are green, red, blue, yellow, black and white. White is useful for LED boards because it reflects more light, some folks think black with gold is attractive. Yellow tends to be more transparent than the other colors.
You can even ask for a specific color to be produced in some cases - of course there will usually be significant extra costs and/or significant minimum quantities associated with matching a custom color.
There's not a great advantage of one over another in most situations. I have used black for PCBs used in a vacuum to increase emissivity.
I just want to add that most manufacturers will indeed charge you money for any other solder mask color than green. The reason for that is that the set-up for different solder mask color is much more difficult and will stop the production line just for your PCBs. But what you can do is to arange the manufecturer to paint your pcb with a legend ink, since usually they have different colors and it's very easy to change the ink tubes.
Of course, if you paint your PCB with the legend ink, you can't print any other ink legend anymore. At least not till the first ink layer is wet. If you are doing high-density PCBs this shoudn't be a problem, because there won't be place for legend anyway. The other option you have is to use solder mask to write the legend in gold or silver, depending on the finish you are using. The manufacturer should be smart enough not to cover anything free from solder mask with legend ink, but you can define it by yourself in the e-data you are sending them.
I'm doing that for one of my PCBs and it's working pretty good so far.
I don't recommend using black for a 1st revision because it's hard to see if a part blew out, but I guess that could be a design benefit on a deliverable...
What colors are available as standard, and why should you choose one over another. Is there a "best" color?
Green is obviously the standard, if you take a sample of 1000 different PCB's from different manufacturers, green is clearly the winner. So if you want a standardized board color, you'd better order green.
If your a rebel and like to go against per-defined standards, then go for purple or orange, or if you really need attention, "hot pink". If you just want something different blue will suffice
Would any of this affect color blind tech people who work on the board?
Yes, you need to implement a system like RHOS to control how much color is on the boards and a require that all products have the correct color of board so that no more color blind people need to suffer.
Colors like green, blue and red are used commonly, as said by others, for lead containing pcb (e.g. solder), RoHs compliant one, and prototype. It's a good choice to distinguish things.
We use black for power dissipation, when we pack a lot of Amps: painting something in black makes a difference. I never noticed effects of lack of insulation, although I confess that I never made an accurate measurement and that the circuits where black soldermask was used are all low voltage (up to 100 V).
