Electronics > Manufacturing & Assembly
Success in fabricating a home rolled PCB
CharlieWorton:
We all know that for the time and hassle involved, hiring a company to crank out small batches of boards for you is superior to doing your own production run. Generally speaking, at least.
But I only need one board at a time, and it usually takes me several iterations to get the circuit exactly the way i want it. So I've been playing with doing thermal transfer PCBs, and have finally got to the point that I'm quite pleased with the result. My first results were horrible; but now, the quality of the traces is quite good. I've attached an example. This is how I'm doing it:
I've found that cleanliness is really important, much more so than I would have expected. I cut the board to size, then wash it in acetone, then sand it with 2,000 grit sandpaper to expose raw copper, then wash it in acetone again. I wear nitrile gloves while doing all this; it keeps the acetone off my hands, and skin oil off the board.
For transfer paper, the best thing I've found is the backing paper from peel and stick shelf liner. In my youth, this stuff was called MacTac; now, it's pretty generic. In Canada, you can buy a 5 foot roll of the stuff for $1.25 at the dollar store. Cut a piece of peel and stick the size of the circuit you want to print, remove the backing paper, and throw the self adhesive shelf liner away. Now print the circuit on a sheet of typing paper, using a laser printer - not an inkjet. Position the backing paper on the sheet so that the backing paper covers the image; tape it down and run it through the printer again, so that your image prints on the backing paper.
The next best transfer paper I've found is the yellow stuff that comes out of China; but the backing paper from the peel and stick shelf liner stuff is as good or better, is cheaper, and is probably available locally. I've also experimented with silicone impregnated baking paper, Betty Crocker brand from the dollar store and that also works not badly (but i think the MacTac backing paper is superior).
Once I have the image printed on the backing paper, I place it in contact with the freshly cleaned copper board, fold the edges around to the back of the board and tape it in place. I then run it through my ultra cheap Scotch laminator ($30 at WalMart in Canada). The machine has two choices: 3 mm or 5 mm. I set it to 5mm, and run it through about 24 times. I think that's overkill, but I haven't yet run experiments to determine the minimum number of times necessary for a good transfer.
Having laminated it 24 times, I then roll it flat using a kitchen rolling pin for about 30 seconds. This ensures that i get excellent contact as the ink cools.
When I remove the transfer paper, I find that I have - usually - 100% transfer. The results - I think, anyway - really are good. I then run it through Ferric Chloride, rinse it, dry it, and give it an acetone rubdown to remove the laser image and reveal the copper.
A few notes on printers. First, it has to be a Laser Printer, not an inkjet. Second, most printers have - buried in the settings - a way to increase the toner density. On Hewlett Packard printers, the range is 1 to 5; the default is 3. Set it to 5, and you'll transfer more toner onto the paper, which gives a superior result.
There's a website - pcbfx.com - that sells a commercial kit for making high quality thermal transfers. They sell laminators, and a very expensive - and presumably, a very good - thermal transfer system. I've not used their products, but they do look impressive. They also have a lot to say about printers, but this only relates to usage with their system. They hate Brother printers, but others on the web are getting good results from Brother printers.
I'm now going to experiment with photo-lithography - using Riston film in hopes of getting even superior results. But I'm pleased with how the thermal transfer is working out. Keep rockin, folks! >Charlie
tautech:
Nice work Charlie and almost word for word replicates my ventures into toner transfer.
A word of warning, once you have a recipe that works some small little change in your gear will change the result so always be prepared to tweak methods to maintain a good outcome.
Waxy backings from Avery labels or similar were my fav too until I had porosity issues with a 600dpi printer and moving to our better 1200dpi one stuffed the whole process up with smudging of the transfer so I had to go to a more poros transfer paper in order to oak in some of the excess toner.
Happy transfers !
jmelson:
--- Quote from: CharlieWorton on February 17, 2020, 05:59:07 pm ---I'm now going to experiment with photo-lithography - using Riston film in hopes of getting even superior results. But I'm pleased with how the thermal transfer is working out. Keep rockin, folks! >Charlie
--- End quote ---
If you can create accurate and high contrast artwork, then Riston will give amazing results. I've been using some form of dry film resist for decades, and it works very well.
Jon
CharlieWorton:
Hi, Tautech! Yeah, I think that thermal toner transfer is incredibly sensitive to small changes. I started out by trying to duplicate others results, and got terrible results. But, when it works, it does work well. The trick, I think, is to define all the variables, and make changes in one area only until you arrive at the right mix.
Hi, jmelson! I'm looking forward to working with Riston - had to order washing soda through Amazon, it just isn't sold locally and there isn't a good chemical supply house nearby. I also have to finish my UV exposure box. Many years ago, I worked as a photo lab technician, and quite enjoyed it. So the idea of working with a photo sensitive product holds some real appeal.
Thanks for the encouragement, everybody! I appreciate it. >Charlie
twospoons:
I've done a lot of toner transfer PCBs over the years. I had quite a good setup using a modified kitchen hot plate with a vacuum compression system for doing the transfer. Best transfer material by far was Press-n-peel Blue. Accurate traces and no pin-holing. As mentioned, keeping everything clean is critical.
Best result: a panel of double-sided Kapton flex circuits, using 5mil/5mil design rules. 23/24 circuits worked (I had hoped for two or three).
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