On 10 Aug 2017 13:57:17 +0000, you wrote:
>Thank you for your comments.
>
>Well, Harvey, covering the pads would be an issue for a SMT board, yes. That is what made me think of using nail polish---it already has a very small brush so you can overcoat the artwork while avoiding the pads. I don't think artwork would ever overlap a pad.
It depends on the board and which layers you use to print the silk
screen. Nail polish is fine, you might want to thin it, though, or
use a thin coil dope (if you can even find that anymore), or perhaps a
decal protector in a bottle from a hobby store.
>
>Now I don't know how durable nail polish is compared to Krylon. I simply thought you might be able to apply it to the top side of a THT board without having to mask the board with masking tape.
>
You can, and I don't see a problem with either nail polish or krylon
other than the application itself.
If you're going to subject the board to that much abuse, then you want
epoxy rather than nail polish, or figure out some sort of transparent
conformal coating, but that's best applied after parts.
I've got some pretty decent boards that had silk screen applied to
them, and while they may be a bit dinged up, they're not that bad.
>I suppose I ought test these coatings to see which coating is more durable for this application. Maybe apply toner to a bare rectangular board divided into four quadrants by a vertical bisecting line and a horizontal bisecting line. 4 identical quadrants laminated with lettering denser than on the average board. I could coat quadrant I with cheap clear nail polish, quadrant II with expensive clear nail polish, quadrant III with Krylon, .....what about quadrant IV ?
I think you'll have an interesting experiment, but not one that's
going to change too much. Applying the coating will be the main
thing.
I think that people have used candy red (I'd prefer green) for a back
board coating, apparently you can solder through it, as it is supposed
to burn off easily.
when I was doing boards, though, I was using mostly SMT parts. Now I
have boards made because they're too complex to make at home.
>
>I'd need to invent some kind of flagrum for beating the board surface equally in all four quadrants in order to scratch it. Just to see which of the coatings is most resistant to scratching that might occur (while populating the board). I suppose I could use some kind of pegboard with through-hole resistor leads epoxied into the holes and sticking out a few mm.
Sounds about right, or perhaps a wire brush for the ultimate torture
test.
>
>This 4-quadrant test might also reveal if any of the coatings change
>the reflectivity of the board--for example, making it glossy where you
>apply the coating and matte where you don't--making it look weird.
>
>Am thinking scratching the board surface is most likely when:
>∗ inserting metal screws into the four holes in the board's corners
>∗ inserting the leads of TH components when populating the board.
>∗ accidentally dropping something onto the board
>
>Am I missing something important?
Hmmm....
soldering iron tip slipping, flying leads when cut, cat/dog/small
child knocking board on floor, damage due to heat of tip when
reworking.
For single sided boards, I once (and it worked) took the silk screen
layer, reverse printed it on a transparency, then glued the
transparency to the top of the board. The printing was on the inside
of the transparency and very well protected. Makes nice decorative
panels and color is easy enough.
You do that before drilling, though.
You want a glue that hardens and does not remain sticky, since that
will gum up your drill bits.
Harvey