What could I use to make colored PCB that is not see-through?

[Spork]

Hello,

I have made many PCB's at home, but they all have a strange green see-through color.
On computers and other devices I have seen a much nicer green, and I'm not sure what it is.

I have thought it may be soldermask, but I looked around and that did not seem promising.
I also found sealant (like epoxy) that has color, but on the PCB's, the "color" doesn't touch the solder points.

Finally, I have also seen red, blue, yellow, and purple PCBs, which makes me wonder what was used.

Does anyone know what I could use to make colored PCB that is not as see-through as my current ones?
I think blue/yellow would look much better because my silk-screen layer is always black.

Thanks,
Spork

 

[House_Cat]

Re: Colored PCB

The color that you are seeing on professional boards is, indeed, solder mask. The mask comes in a variety of colors depending on what vendor supplies the material.

You won't be able to use the kind of solder mask you see on commercial boards for home projects. It is a heat cured resin, and requires application processes that can't be duplicated with simple home equipment.

Home users usually coat their boards with a thin layer of spray laquer for protection after assembly. The laquer can be any color.

An alternative to laquer coating is tin plating the bare board. This can be done at home, but involves toxic chemicals.

If your bare boards are light green when you finish them, you are doing something wrong. The green would indicate copper corrosion. If you rinse your boards after etching, and gently buff them, the exposed copper should be a bright metallic copper color. As the air oxidizes the exposed copper, it will turn an orange-brown color. Brown or green oxidation/corrosion has a high electrical contact resistance and also presents a poor surface for soldering. You need to do a better job of cleaning your boards after they are etched.

 

[Spork]

Re: Colored PCB

Thanks for the info.

I can still but the commercial grade solder mask though, no?
I do my own fiberglass/carbon fiber, and have much experience with curing resin.

As for the green, the copper is fine, here is what I mean from the top, you can see through to the copper on the other side... like its almost clear. See picture.

I assure you that they are etched/cleaned/stored properly. I am talking about the board itself, not the copper traces in particular.

 

[House_Cat]

Re: Colored PCB

OK - the "green" you are seeing is just the color of the resin used to make the board itself. I thought you meant that the copper looked green. The resin color can be different from different manufacturers, but it has to meet the flame retardant specifications for the grade of board. FR4 is the most common these days. The FR stands for flame retardant, and the '4' is the class. I have seen yellowish resin, red resin, black resin, and brown resin - all meeting FR4 standards. The board material in your picture is the most common color. Generally, color additives for the resin are avoided because of the effects on strength.

I doubt you will be able to apply the commercial type of solder mask. There are basically two types - dry film, and LPI (liquid photo imagable). Both of them are photo sensitive materials that are exposed through a film mask. The dry film is applied to the board under vacuum from the opposite side of application, exposed through a mask and developed, then heat set. The LPI is applied to the bare board in a thin liquid layer, set and exposed through a mask, developed and heat set.

A search on the web for LPI or dry film mask should get you more information.

 

[Spork]

Re: Colored PCB

Oh, alright. That is good to know.

I was thinking I could because I have vacuum bags, an oven for curing, and many assorted application tools, but it does seem like a lot of work to color a board. I will research LPI and soldermask a bit more.

Thank you again,
Spork