Intro: PCB Electroless Tin Plating
This is the first is a series of Instructables aimed at documenting all the electronics-related activities that go on at So Make It; Southampton Makerspace (on the South coast, UK) Requests are more than welcome!
On eBay and other on-line sources, you can buy these little twin-packs of tin plating chemicals. I bought some to play with and thought I'd start writing up some instructions on methods to use it.
Step 1: Study the Instructions
Thiourea is apparently quite nasty, so keep this stuff away from food, children and animals.
Don't eat it.
Step 2: Mix the Solution
Add part A into the appropriate amount of distilled water (in my case 250ml.) You can get this from a variety of home and DIY stores, also it used to be used in older 'wet' car batteries, so you could probably get some from a car shop.
Shake it up a bit to get it to dissolve.
Repeat for part B, shaking it around a bit over the course of a couple of hours until there are no undissolved granules. It will have a weird reddish tinge but be completely clear when read for use.
Step 3: Prepare Your PCB
Cleanliness is important when processing PCBs. However, for DIY use, no need to panic. Just clean off the photo resist on the board (you did resist cleaning it off after etching right?) with a little acetone, or gently scrub it off with some steel wool. Careful to get the really fine grade stuff, so as not to make deep scratches in the soft copper surface. You should be able to get the copper to be quite shiny and oxide free.
Clean off any residue in hot water.
You can make a really shiny, polished surface using 'Brasso' copper/brass polish (available in pretty much any household shop in the UK) just place a little onto a cloth, buff the board gently with circular motions, then buff off with another clean cloth and finally rinse in hot water. You don't want any residue contaminating the board!
This will result in almost a mirror finish, however you will clearly see the fiber weave of the PCB substrate material as a pattern in the shininess of the copper. It won't get any better than that. (no I couldn't get my camera to take a shot of that!) As soon a you have a shiny, residue free (don't worry about drying it, just shake off any water) PCB, progress straight to the final plating stage without delay!
Step 4: Immerse in Plating Solution
Simply stick the PCB in a CLEAN photographic tray (or some other tray, ideally with a pouring spout like this one) and pour over the plating solution, so the board is covered fully. Swish it back a forth a little. You will see an instant reaction (with a fresh solution) so don't hang around! Leave it for between 30 seconds and 2 minutes to get a nice flat even layer of tin. The longer you leave it, the thicker it will be, BUT also the faster your will exhaust your plating solution.
Finally, pour the solution back into your container and wash the PCB with some clean water and leave to dry.
Step 5: Final Thoughts
So Make It: Southampton Makerspace
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