How to turn green PCBs from green to black

Why?

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Rich

If that is the case, I would try to negotiate with the customer.. otherwise I think you may be stuck with remaking it all.

Rick C.

Some rather marginal ideas:

1. Mask off any connectors, test points, adjustments, and moving parts. Dip the boards in some kind of black conformal coating and turn everything black. If dipping is unacceptable, spray paint with black epoxy paint. If the customer complains, remind them black is beautiful.

1. Strip off the green lacquer solder mask with paint stripper (methylene chloride). Hopefully, it won't destroy too many components. Unfortunately, it will certainly remove the silk screening. Maybe something a little milder or perhaps a commercial stripper might be better: Stripping will leave the copper bare. Turn the copper black or dark brown with some kind of sulfur compound such as potassium polysulfide, which will probably require that the copper be heated when it's applied.

2. Strip off the green solder mask as above, and use brush plating a black chrome or nickel compound on the copper. Use two brushes to insure a good electrical connection.

1. If the customer is important, give them a very big discount for accepting the green boards. That should provide you with enough time to build and test 92 replacement black PCB's. In other words, make them happy, but not immediately.

I gotta ask... why duz the PCB need to be black? If it's inside an enclosure, notbody will see it. If you're using G10/FR4 for radiating some heat, the color won't make that much difference, especially inside an insulated (adiabatic) enclosure.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Seems the board is full of LEDs and I expect the black is the intended background.

Rick C.

On Thursday, August 9, 2018 at 11:51:27 PM UTC-4, snipped-for-privacy@gmail.com w rote:

ckground.

If this is correct, so far I like the black paper or plastic sheet with hol es for the LEDs. That should work better than black solder mask.

I was looking at making an enclosure for an LCD display once using a COTS b ox. The box I liked best had a clear plastic lid covering the entire top. I would have used a sheet of plastic with a hole for the display area so n othing showed but the display. The job never materialized.

Rick C.

Thanks. I didn't see any mention of LED's, but if that's true, then just masking off the LED's:

862 - Peelable Latex Solder Mask and spray painting the PCB with black epoxy paint might be easier than punching holes in a paper mask. The good news is that only one side of the PCB needs to be painted, so dipping is probably not necessary.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

If the board is already stuffed that's probably the only practical option. Not convinced it needs to be epoxy though.

NT

I like the laser-cut vinyl (or a Cricut knife cut overlay) idea.

Alternately, you could use a roller to apply something gummy and hydrophilic (tapioca? washable solder mask?) on the LED surfaces, and spray with black lacquer; the water-soluble bits will be easy to wash off when the paint dries.

Get black laser cut sticker (vinyl) that has holes for the LEDs and apply carefully ?

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mikko

Or a thin PCB, routed to suit and painted black.

Cheers

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Clive

Jeff Liebermann wrote in news: snipped-for-privacy@4ax.com:

Modifying the PCB like this is the last thing anyone would ever want to do in any circumstance.

The only mask free PCBs I saw or used were ordered that way. Or HV boards were one example. It maximizes one's capacity to extricate any remaining water and it makes for superior potting media attachment.

His fix:

Add a coating to the existing board. Be carefull to test the chosen medium first for conductivity and reject choosing any that are.

Application can be via pre assembly mask and coat, or post assembly mask and coat. I would choose post assembly here as masking each hole is harder than masking each LED. Also post assembly works as your chosen coating then has no thermal considerations to worry about with assembly. You could then bake it on at whatever temp the assembly is able to handle.

There are plenty of matte black paints out there.

snipped-for-privacy@gmail.com wrote in news: snipped-for-privacy@googlegroups.com:

Less likelyhood that it would have any conductivity?

"Tim Williams" wrote in news:pki4an$i1t$1 @dont-email.me:

Yeah... Use one of those MAP torches on it and let the little 'dead soldiers' coat it. ;-) Don't worry about the new conduction paths or obscured LED windows.

Yes, that's what I was thinking. It also handles the heat if there are power devices on the PCB. In the distant past, when I was working with conformal coatings (acrylic, urethane, epoxy) for waterproofing marine radio PCB's, epoxy was the best combination of adhesion, high resistivity, dimensional stability, and high temp. The down sides were that it was impossible to rework the underlying PCB, and would crack if the PCB was flexed. The solvent used was xylene, which is banned by the People's Republic of California, along with other VOC's. Instead, I suggest one of the water based epoxy concrete floor covering mixes, which should work as well. Finding epoxy floor covering in flat black might be a problem, but methinks adding some granular carbon black or graphite to the mix should do the trick. The stuff is conductive, but as long as you DON'T use carbon graphite flakes, it won't conduct when suspended in solution. The carbon and graphite granules are roughly spherical, and do not touch each other.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

To provide contrast for the LEDs.

Hint: Like an attorney or doctor, I never offer exactly one solution. I offer two or more. The benefit is that if the client chooses the wrong solution, it's his fault for screwing up, not mine. Sometimes, I include at least one really bad idea, so that the client will be distracted, and makes my more serious solutions look comparatively more attractive. I believe this is somewhat of a "red herring".

Yet another idea. Removable rubber paint: Spray it on and everything turns black. If the client doesn't like it, peel it off and try again. Maybe ship the product with 92 cans of "touch up" paint.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Further to that, if you lightly mist the PCB with pure distilled deionized water you can place and move the vinyl as it won't stick until the water evaporates. This way you can get the placement exactly right. Once in perfect placement use a rubber mat style press (I'm thinking book press - similar to the kind Gutenberg used) to squish the vinyl down and push the remaining moisture out.

Here is an explanation:

That is how we place vinyl on control panels and the like - but we simply use tap water as who cares if it is conductive on a metal panel...

John :-#)#

I would try a black magic marker preferably on a junk board to see if it is good enough for you and your customer. And if it is good enough hire a high school student to do the boards. Lo tech ,but low cost. and almost no cost to try.

Dan