Professional looking PCBs

Hi!

You know those professional PCBs that look greenish, rather than the paler, semi-transparent light green usual color of a glass fiber epoxy laminate?

Once I made my own PCBs, how do I make them look "pro"?

Do I have to use a spray? What kind of spray? Will it be easy to spread it in a even way?

Don't get me wrong, I want this primarily because I think the PCBs will resist better to age and oxidation.

Thanks! John

Reply to
JJ
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The (usually) green stuff on professional boards is actually a solder resist coating that is screen printed onto the boards. It stops the wave soldering machine shorting out tracks.

This site

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"After soldering, conformal coating like Plasticote 70 from CRC Industries can be used. This conformal coating provides a thin layer of electrical isolation but also allows repair soldering without first stripping off the coating"

There are several companies that do small PCB on the cheap and some will do solder resist for not much more.

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Reply to
CWatters

That is called solder mask and it can be silkscreened on or applied photographically...that process is called LPI (Liquid Photoimagable Soldermask). Your decision will be based on the thickness of mask you can tolerate. With surface mount there are some issues if the mask is too thick....Like the previous post suggested, just call a local prototype circuit board shop and get a quote. Their engineering department should be able to suggest a product that will work for you. Look under printed and etched circuits in the yellow pages or just do a google search.....good luck, Ross

Reply to
Ross Mac

On Wed, 12 Nov 2003 15:26:45 GMT, "CWatters" Gave us:

No. The solder mask layer is just that. Another physical layer on the board.

It is a photo etched film that basically, but not always and everywhere., follows the pad layout of the board.

There are different colors available, and different materials as well. It is film stock, however. Laminated onto the board, just like the circuit layers are.

It is NOT silk screened onto the board.

FR4 PC board layers are yellowish in raw form.

Reply to
DarkMatter

On 11 Nov 2003 22:17:24 GMT, snipped-for-privacy@invalid.com (JJ) Gave us:

Raw laminate is usually a yellowish color. It also actually depends on the media involved, such as FR4 or G10.

You can't. Not with the circuit fabrication process you seem to be referring to. What you need to think about is post assembly conformal coating of the board, or full potting (which hinders servicing).

Conformal coating still allows direct access for servicing, whereas fully potted assemblies are harder to service, and require reliable circuits for trouble free operation.

Yes. Do a search for "Dolph's AC-43"

See above

It is a spray. You apply it drippingly heavy. Let it dry, and apply it again. Let that dry in air for an hour, then bake it at 175F for a couple hours.

Oh yeah... You have to solvent clean the PCB after assembly, but BEFORE any electrolytic caps, OR transformers or chokes go on the board. Then add those mentioned parts, being careful to spot clean the solder flux on the solder joints after each part gets added, before the flux solidifies, as it is easier at this time. Use water soluble solder and flux, not RMA. Use hot 90% IPA ($12 gal) for the solvent step, if you do not have a Pro solvent ("EnSolve" they are like $35 plus a gallon).

After that clean step, you must bake the board out for an hour or so at 175F. As PCB material is hygroscopic (draws water in), you will want to dry it out real good.

The conformal coating will make your assemblies reliable for years.

Reply to
DarkMatter

resist

soldering

That's interesting...then why do most PCB companies still have a silk screening area for applying soldermask and legends. I have a good friend that manages the area. It is not the norm anymore since LPI, but they do it on short runs if the customer allows.

Reply to
Ross Mac

resist

soldering

Hey, have you ever seen how the PCB shops remove soldermask from an area that it should not be? They used to just scrap out the whole order, but now they use a laser drill and just ablate down to the surface. The customers seem satisfied with buying the boards.....Just an interesting factoid there.....Ross

Reply to
Ross Mac

On Fri, 14 Nov 2003 21:47:19 GMT, "Ross Mac" Gave us:

The only thing silk screened on a PCB IS the legend/reference designator/logo. The printed info.

The solder mask itself is a laminated film.

Whatever. Read the topic again. I still contend that if it was not a pro board to begin with, there is no real way to make it "look professional".

Reply to
DarkMatter

On Sat, 15 Nov 2003 22:04:54 GMT, "Ross Mac" Gave us:

Film masks are ONLY applied to those areas where they are specified to be applied. Areas that are without mask never had it to begin with.

Reply to
DarkMatter

message

now

That's true, but mistakes are made and fixed with the laser drills...that was my only comment there!

Reply to
Ross Mac

it

I'm sorry, that is incorrect too. Legend is also applied with film, nowadays. On an occassion, soldermask and legend are applied the old way, via screen printing....trust me, I spent close to 30 years around that business!

Reply to
Ross Mac

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