hi,

i have thought of simply dipping a newly etched board (drilled as well) in a clear wood varnish simply to prevent oxidation (its quite cheaper compared to other commercially available pcb-specific products)

the problem is, if i dip the whole board in varnish (w/o components) the the pads would be covered with varnish. if those pads were already covered, then i still need to scrape the varnish off so that i can solder components. isn't it would be tedious for a 100+ hole board to scrape off varnish before soldering?

is there a way for me have the pads covered first, then easily remove the covering after applying the varnish?

 

It seems to me that using a spray type covering would work better here. You can solder everything in, then spray the copper side with a varnish. This way, you wouldn't have to mess with scraping, or covering the pads before you spray. They sell cans of varnish for about $3.00, and should last quite a while (5 or 6 PCBs).

One point of consideration: I'm not sure if varnish is actually conductive in any manner, so you may want to test to see if the varnish is conductive. You can spray a layer on a scrap piece of plastic, let it dry, then see if the varnish is conductive using a continuity tester. If it conducts, the varnish idea wont work.

Another point of consideration:
I'm not sure if the varnish will react with the rosin used in solder, so you may want to make sure your board is pretty clean of rosin / flux. Otherwise, the varnish may bubble up in the areas that the rosin covers. You may get lucky, and find that these two wont react, but I think it is a worthy thing to find out. You could probably test this by taking a scrap piece of PCB, solder some drops onto the PCB, then cover with the varnish.

Good luck!

 

u cud get round stickers the same size as the pads then once itz dried peel off the stickers? (havent actually tried this so it mite not work)

 

whether or not it is conductive is a very important matter. I would NOT just check using a continuity meter as those typically only call it conductive if they sense less than 100 ohms or so. but if the varnish were to act more like 50k ohms and change with applied voltage, it would be a disaster to most circuits(especially analog ones). You'll have to do some initial extensive testing on the stuff before you should trust it enough never to think about it again. You would only have to do it once and then if it checks out, only use that brand.

 

in that case, then the components would also be covered with varnish, right? won't there be any problem with "desolodering" in cases wherein one component malfunctioned, rom reprogramming, etc...?

 

If you only sprayed the bottom (copper side) of the PCB, the components should not get sprayed with the varnish, unless you're working on a double sided copper PCB.

In the cases where desoldering is needed, you could gently scrape off most of the varnish and desolder normally.

 

You don't want to dip the PC board before mounting the parts. If the bare board is going to sit around a long time, put it in a zip-lock bag. I have used polyurethane floor varnish to dip finished boards with no leakage problems. Be sure to clean the board well before dipping.

__________________
see my website: www.geocities.com/russlk

 

actually yes! i am targetting double sided boards...

 

a can of insulation used on PCB is around $6 and is 160ML in volume.. would last enough..wht need to be cheap playing around with wood varnish.. one thing i know is that wood varnish is flameable and contains petroleum derived hazardous materials.. if ur pcb heats up a bit like 60C or soo.. many varnish types will start giving dangerous fumes as well as damage to varnish layer..using varnish = not a good idea at all..

btw when u r soldering on a varnish covered board.. imagine the smell and fumes.. and mess.. yuck...

 

Easiest solution... use Kontakt Chemie SK10 Laquer Flux (spray). You can solder through it, whilst it protects all the copper. It Improves solderabilty. Has the advantages of varnish, without needing to scrap pads for soldering etc. I use it all the time here. Direct link to my supplier here>> http://www.rapidelectronics.co.uk/rk...0093&XPAGENO=2

Steve