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.