Finishing off PCBs

[bopmachine]

OK, I'll give it a go. I have just recently burned my first PCB. I used the press-n-peel method. Worked great after a few, er... test cases. Now I am thinking how do I finish it off? Do I need to tin the traces, varnish it or something? I've never made a PCB before and am flying by the seat of my pants.

BTW I am making a Gyaf audio's pultec inspired passive EQ.

[triez]

You have a couple of options - you can go to an electronics store and buy aerosol lacquer which you can spray onto the PCB ( after you clean it carefully ). This lacquer is designed almost as a kind of flux, so it protects the copper but allows you to solder through it.

If you want to go further, you can instead buy a tinning brush which is a solder iron tip that allows you ( after coating the PCB with flux ) to brush molten solder onto the copper tracks to coat them.

Lastly, some good electronic stores sell a chemical which you can use to electroplate silver or even gold onto the copper.

[EveAnna Manley]

Hi Triez,
Could you post a link for that tinning brush? I don't think i have ever seen one.

When we are making copper prototypes we use a liquid flux on the copper and then a standard tip to heat solder and smear it around over the copper traces.

[bradavenson]

You also might consider a spray on conformal coating. It makes it more difficult to repair later, but will protect the board from all sorts of evils. Something like the Fine-L-Kote™ SR Silicone Conformal Coating :
http://www.techspray.com/pindex.htm#2100
http://www.mouser.com/catalog/615/1036.pdf

[gyraf]

I like to use SK10 Flux from Kontakt Chemie, e.g:

http://www.mantech.co.za/kontakt/K10.htm

This is both solderable and a good protect against humidity and occational pcb trace oxidation. Good isolation properties also..

Jakob Erland

[triez]

The tinning brush thing was something they used when I worked for Telecom years ago, I am not sure where they came from. I think it worked by capiliary action, you just applied solder to it until it was full and gently brushed it onto the track. I will try and find out more...

[EveAnna Manley]

Triez, You are not talking about a solder wick which comes on a little sppol and looks like a flat braid of copper are you? A solder braid is usually used to remove solder from a board.... but hmmmm I wonder if you put a bunch of solder on it then it would "brush" it on like you say? I guess that would work tho'. I have never tried it. (I haven't tinned any copper boards lately anyway...)

[triez]

No, not the good old wick, but I have been thinking about what I saw back in the days I worked for that company, but I didn't pay too much attention to the iron then as I wasn't using it. I guess it must have been a tip with copper or brass bristles that worked by some kind of capilary action after you blobbed enough solder onto it. I looked on the net at some of the iron companies but cannot see anything there, I just assumed that it was a commercial product but maybe it was an in-house invention.

[Tim Farrant]

If you are going to tin the baord by hand, make sure you do not over heat the tracking. The foil will lift off the substrate very quickly and render it unreliable.

What is the circuit ? If it's just low current stuff, I would tend to seal it and forget the tin plating.

Cheers
Tim.

[Kev]

If it is a home made PCB -
then I always clean .. as bright and shiney as I can and then , without putting your greasy fingers all over the copper , spray with a lacquer.

But then I think most of you guys already know I do that as some of us have discussed this before.

Good luck with the press-n-peel technique.

[EveAnna Manley]

Update on the Tinning brush. A thoughful reader emailed me a link to the Bürklin website
where he found the aforementioned tinning brush:

Tinning inserts, type Tin–A–Print (L177.100)
for rapid PCB tinning. The soldering tool insert consists of a brush with special metal bristles which produce a capillary effect and permit the tin to be applied evenly without creating bridges and blocking the holes.

Mystery solved!

Thank you gentle reader...

[triez]

Well spotted! I looked for info on the net for ages and couldn't find one and thought as I mentioned before that they must have been discontinued or custom. Definately worth a try I think...