Tinning a PWB
I have tried a variety of ways to tin the traces of a PWB I made
over the years, from trying to tin bare copper traces with solder
and iron to using various chemical baths like "Tin It". I did not
invent this but found it on
the internet and found it worked very well for my needs. I
tried various flux compounds available in the US and settled on the
Oatey #95 Lead Free Tinning flux as working the best for me.
Sometimes the old ways are the best. This will give a very thin even
coat of tin to a board.
You will need:
A slug of solder
Soldering Iron
Aluminum Foil
Acetone
A metal file
Brush or Q-Tips
Oatey #95 Lead Free Tinning Flux , 1.7oz container. (A Home Depot
item in plumbing.)
Paper towels or tissues
Making the solder slug.
I found a slug about the size of a quarter worked best for me. Just
something I found I could hold on to easily.
I made a melting cup out of heavy duty aluminum foil by placing the
foil over a cup of a muffin or cupcake tin then using a drinking
glass to press the foil into the cupcake tin.
Trimmed with scissors to the top of the cupcake tin. Now that you
have a cheap disposable melting cup, make the solder slug.
Melt some solder (I used larger diameter solder meant for plumbing
and I wont use electronics) in the cup with the iron. Keep feeding
in solder until you have the slug size you want. Now let cool and
remove from the melting cup and knock off the rosin core left
behind. Also of interesting note, if you use a de-soldering pump
(Solder Sucker) don't hesitate to empty the leavings from the pump
into the melting cup. Recycling at its best.
Clean the board of etch resist with Acetone. Place the PWB on a
tissue or paper towel when doing this as the dissolved etch resist
and acetone gets wicked away by the paper towel. I usually just soak
the end of a tissue in the acetone, then rub. If you have a stubborn
spot, use a flux brush from Home Depot, (with the welding supplies
Model# KH589). I found them much cheaper at Harbor Freight (36
brushes for about $3.00, Item# 61880). I do however, cut the
horsehair bristles short to give me a stiffer brush.
Once dry of the acetone, use a Q-Tip or a or other swab to coat the
PWB with a very thin layer of the Oatey #95 flux. Thin, meaning no
visible grey lumps of flux.
The next part is kinda fun, and where the magic happens. Think of it
like grating cheese. Take the file in one hand and the slug of
solder in the other and hold it over the PWB. Now grate the solder
slug with the file over the PWB. It dose not take much, in this case
less really is more. When you see a dusting of the solder filings
stuck in the flux, stop grating the solder slug.
Now take your soldering iron and run it over the traces of the
board. Once the traces warm up, the flux with the dusting of solder
particles will melt nice and even over the traces.
Now clean the board again with Acetone to remove the remaining flux
and left over solder particles. Do examine the board for solder
bridges. If you dust the board with too many of the filings, it will
make solder bridges so using less is better. You can always dust
with a little more if you missed a spot.
One final note, the original article referenced suggested
doing his before drilling the board. You may have to clean out the
holes. I find that drilling the holes before removing the etch
resist works better for me. The contrast between the etch resist and
bare glass or phenolic material is much sharper and easier for me to
see, center and drill the holes. Try it both ways and again use what
works for your eyes, hands, skill and ability.
The solder slug I made is still in use. When it get too small for me
to hang on easily, I just make a new melting cup, put the slug in it
and heat it up again. Then melt some new solder with it. Its gotten
to where I keep a zip lock bag and dump the leavings from my solder
sucker into it then add them to the melting cup when the time comes.
If this works for you email me.