Need some kind of substance...

[throbscottle]

I did my first attempt at through hole plating this weekend, and it went fairly well, barring mishaps due to too little care in my enthusiasm to produce something! Things started to go wrong however when I attempted to give the board a coat of solder resist, because it gets in all the holes and gums them up.
So, any suggestions for a substance I can use to plug the holes, will clean off the face of the board easily whilst leaving the holes plugged, and finally will come out of the holes easily when resist is finished and not interfere with solder tracking through them?
So far all I can think of is wax or styrene but neither will clean off easily!

 

[gophert]

A solder resist has nice clean shapes that prevents the stuff from going where it shouldn't so it can steer the solder to go where you want it to go. It would more like you are adding a conformal coating - or simply spray painting the board. What exactly are you doing?

Also, remember, if you are the only person who has this problem, there must be a better way of doing it (or it doesn't need to be done).

 

[KeepItSimpleStupid]

Use a dry film. Fortex - Dry Film Solder Mask (DFSM) for PCBs
www.fortex.co.uk › product › dry-film-s...

 

[throbscottle]

Gophert, it's liquid photo-sensitive solder mask, you coat the board with it, cover it with a mask to hide the pads, then expose to UV. This hardens the mask everywhere except the pads, which you can then clean with acetone. Been working really well on un-drilled boards, but holes already being present is definitely a problem.
KISS, I will look into that but it probably doesn't suit my budget...

 

[alec_t]

If you've got only a few holes to deal with, could you just temporarily insert pins, nails etc? With luck, capillary action wouldn't be enough to draw the mask into the holes. Of course, if you've got lots of holes .......

 

[gophert]

Gophert, it's liquid photo-sensitive solder mask, you coat the board with it, cover it with a mask to hide the pads, then expose to UV. This hardens the mask everywhere except the pads, which you can then clean with acetone. Been working really well on un-drilled boards, but holes already being present is definitely a problem.
KISS, I will look into that but it probably doesn't suit my budget...

If it can be cleaned with acetone after application, can you do the photo mask and then drill And plate?

 

[throbscottle]

Lots of holes. Nails and pins wouldn't be any good because the resist needs have oxygen excluded or it won't harden, a thin sheet of plastic does the job nicely, wouldn't work with all those nail and pin-heads!
Apart from which , I'm going to try going down to 0.3mm vias for the next one (well, maybe), so I might struggle to find anything to fit. That said, it doesn't matter about keeping the resist out of the vias, unless they miss getting plated (and on this first board my success rate is about 90% of holes plated, which I'm actually quite pleased with!)
I did consider the same idea but with some kind of plastic filament, trimmed flush.
I've started building this board with no resist as it is. Just a bit of a shame is all.
Nice idea gophert, but the problem would then be how to plate the bits that are isolated from the rest. And the nature of pcbs is just that, lots of isolated bits.
It's more of an issue that the holes let air in (and mask leak out), than the non-wicking of solder.
Maybe I should just use a conformal spray, and feel slightly sad about it...
I wonder if plasticine would do the trick?

 

[throbscottle]

I think commercially it's applied with a silk-screen so hole penetration isn't an issue.

 

[tomizett]

So far all I can think of is wax or styrene but neither will clean off easily!

Paraffin/candle wax should work - it will poke out easily and works rather like a flux when soldering, so any residue is not a problem. However, while it will keep the hole itself clear, I don't see how you'll keep the resist off the pad surrounding it.
Good work though - I had no idea that through plating was feasible for the home enthusiast. Let us know how you get on!

 

[throbscottle]

tomizett, the resist covers the whole board, and after exposure the parts which were masked from the UV light (ie, the pads) it can be cleaned off.
My only issue with wax is that it will be hard to clean off the face of the board - it needs to be clean or the solder mask will just peel off when it's cured!
Paraffin wax might be better for it than candle wax though. Wonder where I can get a bit to try...
There are a few guides and videos around which describe making your own plating solution, but I decided it was cheaper to just buy the refills for Classic Plating's kit (since I don't need the whole kit), and the actual plating itself was very easy. I'm going to try a different recipe for conductive ink though. I'm using PVA as the binder at the moment and I don't really like it. Going to try gum arabic.

The other substances that occur to me are latex masking fluid and "mod podge" both used by artists, expensive and I have no experience of them.

 

[schmitt trigger]

Without actually having tried it, I also like the paraffin idea;
You could dissolve it afterwards with some gasoline (petrol). Although I ignore whether the solder resist would resist it or not.
Sorry, I could not resist the pun.

 

[tomizett]

tomizett, the resist covers the whole board, and after exposure the parts which were masked from the UV light (ie, the pads) it can be cleaned off.

Of course... yes you said - it just didn't sink in the first time!
So, you need to be able to fill the holes and then clean the flat surface of the board...

 

[throbscottle]

Actually my (non-technical) daughter suggested PVA adhesive when I explained the problem to her. Hopefully it would dry enough on the surface to peel off and remain tacky enough in the holes to keep them filled. Possibly add a filler to it like chalk.

 

[gophert]

Actually my (non-technical) daughter suggested PVA adhesive when I explained the problem to her. Hopefully it would dry enough on the surface to peel off and remain tacky enough in the holes to keep them filled. Possibly add a filler to it like chalk.

PVA adhesive doesn't stick well to certain substrates and it also shrinks a lot while it dries - that combinati9ns creates a problem when used as a coating instead of an adhesive (bonding two surfaces). Try it and reward your daughter if it works.

On the same arts-and-crafts thinking, you can get some adhesive-backed vinyl and a leather punch (for punching small holes) and make some nice round stickers that can be placed on the pads. Good vinyl labels should be able to hold back a flood. FedEx print stores have exterior vinyl that is nearly indestructible without acetone. Check your local digital printing shop if FedEx is not in the UK.

 

[unclejed613]

Paraffin/candle wax should work - it will poke out easily and works rather like a flux when soldering, so any residue is not a problem. However, while it will keep the hole itself clear, I don't see how you'll keep the resist off the pad surrounding it.
Good work though - I had no idea that through plating was feasible for the home enthusiast. Let us know how you get on!

"back in the day" when i worked for a prototyping company, some of our clients used a silicone rubber filler in the holes and vias. i don't know what they used to remove it, but every once in a while i needed to poke out some through-hole vias where they had missed removing some of it. it was easy to see because it was pink colored.

 

[throbscottle]

Ahhhhhh, so there's an actual /thing/!

 

[throbscottle]

On the same arts-and-crafts thinking, you can get some adhesive-backed vinyl and a leather punch (for punching small holes) and make some nice round stickers that can be placed on the pads. Good vinyl labels should be able to hold back a flood. FedEx print stores have exterior vinyl that is nearly indestructible without acetone. Check your local digital printing shop if FedEx is not in the UK.

I did think about the same idea but using photo resist that I used when etching the board, but it's thicker than the solder resist needs to be so problems there too.

 

[throbscottle]

"back in the day" when i worked for a prototyping company, some of our clients used a silicone rubber filler in the holes and vias. i don't know what they used to remove it, but every once in a while i needed to poke out some through-hole vias where they had missed removing some of it. it was easy to see because it was pink colored.

Could it have been latex?

 

[Western]

I'm probably way off the mark ... but this stuff keeps coming to mind ... and it is latex.

It's a Peelable Coating Mask made by Electrolube ... PCM250ML

 

[throbscottle]

I'm probably way off the mark ... but this stuff keeps coming to mind ... and it is latex.

It's a Peelable Coating Mask made by Electrolube ... PCM250ML

Certainly looks interesting, though I wonder if it's possible to peel it off the surface whilst leaving it in the holes. Pricey stuff, too. I'll put it on my "maybe" list.