DIY solder-resist or something like that?

[Tomble]

Hi again folks, long time no see!
Been on a bit of a hiatus from electronics, but am looking at getting back to my crappy old PIC programmer circuit now (yet again).

Last I was doing with it, I'd got the design and layout done for the final board, and made a horrible little case for it, but I had a bit of a stumbling-block with one particular part where I need the pin of the ZIF socket to pass through a hole in a track (it's all on stripboard!) without being electrically connected to that track. The track is carrying the data signal (or is it clock, I forget), and won't want to be taken a more roundabout route, and the pin going through it is just going to a pull-down resistor to ground, so isn't too critical, but I don't want them accidentally shorting each other.

(in case it's actually necessary, I made a little diagram, but the first half of it may actually make things more confusing. The hole isn't meant to be at the edge of the board, that's just how I drew it... )

So anyway, although the pin doesn't connect to the track it passes through, it will connect to a short solid wire-link to the resistor a cm away, so it's not as simple as merely putting a PVC sleeve or such over the pin (it'd melt to goop when I try soldering it at that short distance I think), and I'm thinking I'll need to put something on that patch of track to prevent any solder bridges forming between the pin/wire-link and the track. Does this make sense?

I don't have any proper solder-resist, and really don't want to buy anything just to do this (except maybe something very cheap from the shops), I figure something like a small piece of greased/waxed paper around the base of the pin. But I don't really want to just try something on a whim and screw up my rather elaborately prepared board and an hour or so's soldering. So anyone got any experience with this, or good ideas/advice?

 

[DirtyLude]

For non-conductive insulation for part that don't heat up, I would use a simple hot glue gun.

 

[Speakerguy]

Kapton/polyimide tape. Wrap around the pin, or just place over the trace and make sure the edge of the trace can't short to the side of the pin when you apply it. It's cheap, heat resistant, and used for electrical isolation on circuit boards all the time.

**broken link removed**

 

[Mr RB]

Use a 45' taper countersink tool, or even a drill bit to remove the copper immediately around the hole.

That will still leave the PCB hole small (to support the pin) but the copper part will have a big hole well away from the pin.

 

[Tomble]

Hi again, thanks all for your ideas

Use a 45' taper countersink tool, or even a drill bit to remove the copper immediately around the hole.

That will still leave the PCB hole small (to support the pin) but the copper part will have a big hole well away from the pin.

*nod* Actually I'd already done this a tiny tiny bit with my stripboard cutter, but didn't want to do too much as there isn't much track around the holes as it is. I also figured it'd be preferable to also add a physical insulator to be on the safe side, but perhaps it'll be enough on its own after all. I'm probably just being paranoid after too many misbehaving circuits!

What I think I'll do, is expand that hole in the copper a tiny bit more, solder everything else in place, trim the other pins+legs so they don't get in the way, and then stick a tiny disk of card with a pinhole or slit in over the pin I need to do and solder that. Then take the disk away and try to wrap a thing of greasy paper around the pin and inside the hole, to give a bit more protection just in case. Then fix that in place with superglue perhaps (if it needs to come out again there's always superglue solvent available). Any obvious flaws with any of that?

Whilst I'm here, can anybody tell me why my recent posts often seem to appear all crunched up in a column on the left? It looks terrible and I'm sure they didn't used to do that when I first joined (I think the forum software changed since then)...

 

[shortbus=]

Instead of your greased paper why not do as RB said and then center the pin in the hole and fill the hole with 5 minute Epoxy. You could hold the pin in position till the Epoxy set up. This would be done after your soldering of course. And use the clear Epoxy.

 

[Tomble]

Instead of your greased paper why not do as RB said and then center the pin in the hole and fill the hole with 5 minute Epoxy. You could hold the pin in position till the Epoxy set up. This would be done after your soldering of course. And use the clear Epoxy.

Actually I considered using epoxy too, after hearing DirtyLude's glue-gun idea. What put me off it particularly though was AFAICT it's basically unremovable once set, and it'd be just my luck I'd need to change or undo something later, or completely redo the board from scratch (and those ZIF sockets aren't cheap enough to just throw away!). Hence the idea of using superglue, which at least in theory can be redissolved.

It's a bit like how my old flatmates and I came to the conclusion that putting the lid back on a computer after opening it to work on was bad luck... because we'd invariably need to get back into it again!

What's significant about clear epoxy BTW? AFAIK we only have plain old Araldite in the house, which ISTR is cloudy white.

 

[shortbus=]

Some of the Epoxy has conductive elements in it. The black colored has carbon black, J-B weld has aluminum powder and so on. Epoxy is not heat resistant and will break down with heat, (as will super glue). Even super glue is some what conductive, I ran a wire EDM machine and when cutting multiple parts(stacked) we held them together with super glue. A wire EDM uses a electrically charged moving wire to cut metal parts.

 

[Mr RB]

My electronics toolbox has a little bottle of nailvarnish, it's a handy tool for spots of paint or to dab on a screw to stop it from vibrating loose etc. I've even used it to draw tracks on PCB before etching, and to varnish hand wound inductors to stop the coil moving etc.

Get the "quick drying top coat" it's much faster to dry hard and I collect them after my woman has emptied most of it because the last bit in the bottom has less solvent and drys even quicker.