Introduction: PCB Etching.. With Vinyl!
It's rather unheard of, using adhesives like vinyl as an etch resist. People typically use laser printers and transfer the toner from glossy photo paper, or they use UV lights and images of their circuit printed onto transparencies to develop a photoresist.
While both of those methods yield proven, quite repeatable and often very accurate results, I didn't have a laser printer, nor these UV lights I saw everyone using. (I later learned that normal fluorescent lights work too.) So, at a loss and with a desire (and also need) to create some PCB's of my own, I looked at the tools I had and thought: "I wonder if it's possible to use my vinyl cutter to make an etch resist?" Well, just in case you have the same questions, I wrote this Instructable.
I gathered a lot of my courage to try this method after reading this article on Make:, and I see now that another user here also used vinyl. I figured it wouldn't hurt to try it, so read on to see what I did and how it went.
Note that you will see two different PCB's in this Instructable; I didn't take a plethora of photos but both used the same processes to make the etch resist.
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Step 1: Design Your Circuit and Export It
Quite obviously, you'll need a circuit to etch onto your PCB. I used the Lite version of Eagle 6.4. I won't get into the aspects of PCB design or how to use Eagle, as there are many tutorials elsewhere online. I will just assume you are reasonably fluent with Eagle.
Once your circuit is all drawn up, you'll need to export it. My vinyl cutter's software allows the use of DXF files, but the files exported from Eagle were not going to be easily used, so I opted to export an image.
The vinyl cutter I'm using is the Silhouette Cameo, and the software is Silhouette Studio. It features a function that allows you to import an image, and it can trace lines in it and create a vector image that the cutter can cut. I will be assuming you have already learned how to use your vinyl cutter, so I won't be getting into that here.
When I exported the image from Eagle at the standard settings it was very poor quality, and I feared that it my vinyl cutter's software wouldn't be able to accurately create a vector image. So I exported another version of my PCB image, this time at 1200dpi. This led to improper scaling in my cutter software, but I had a solution.
Eagle has a measurement tool of sorts, but I decided that rather than fight with that, I would draw a rectangle the width of the widest parts of my circuit. I made sure that it was as close as possible without having to zoom in unnecessarily, and then I clicked the information button and clicked on my rectangle. In the dialog box that appeared, it listed the width and height of my rectangle; bingo! This is what we would want. Write down that number and go back to the cutter software and scale your vector design of your board to the same width as the rectangle you took the measurement of. Make sure to keep the aspect ratio, so your design scales evenly and doesn't just stretch wider.
Step 2: Cutting!
There isn't really a lot to this step; just run your program and have the vinyl cutter cut. It might take some adjusting of settings to get the results you're after (I had problems of not cutting deep enough, or parts lifting off the backing).
Getting the right cut will vary a lot from machine to machine, and material to material. It's best that you get used to cutting with your machine first so you know what settings work best.
Step 3: Prepare Your Copper Board and Apply Vinyl
Get your copper clad board prepared (clean it off; I scuff it as well but that is up to you) and cut to size, and get your vinyl transferred to the board. It's not super important that you get out all air bubbles, but it helps.
Some people prefer to "weed" their cuts (remove material that you don't want/need) before applying the vinyl, but I prefer to weed it after it has been applied. Both have their ups and downs.
It was at this point that I also tried something else; after I applied my vinyl etch resist (in the pattern of parts I want to keep from etching), I took my etch resist "negative" (the vinyl that had surrounded the traces) and placed it beside my etch resist on the board. I took some nail polish (paint works too) and brushed it on the negative, and made sure I covered all of the exposed copper within. After this, I peeled off the negative and was left with two identical patterns on the board; one made from vinyl and the other from nail polish.
On the larger board, I did two separate cuts and used the positive cut for one etch resist and used the negative cut to make the other.
Once the nail polish/paint was dry, I moved on to the next step.
Step 4: Etch!
Now, it's time to etch your circuit board(s)! I used an ammonium persulfate and water mixture to etch my boards, but some people prefer ferric chloride, sodium persulfate, or other chemicals. Make sure you do this in a well ventilated area, as these etchants create gases that are pretty bad for you. (Or so I've heard. Best to be safe, especially with chemicals!) I checked on my boards periodically and stirred the mixture a little each time, to get fresher etchant onto the board. When I could see no more copper exposed on the board, I took it out of the etchant with some plastic tongs and rinsed off the board in a small container of water. Make sure you mark the containers, utensils and whatnot that you use for etching so that nobody accidentally uses them for food or other purposes. There is a reason for the warnings on the chemical containers!
Dispose of your chemical mixtures with proper care and according to local guidelines. Ammonium persulfate is good for quite a few etches so if you're making multiple boards don't bother mixing a new batch for each board.
Step 5: Results
As you can see, on the smaller boards the nail polish worked much better than the vinyl alone did, other than the one part where I moved the negative. I am not sure why, but I got tiny circles of partially etched copper on the vinyl mask for the little board. On the larger boards I made sure there were no air bubbles on the board by gently scrubbing it with a brush in the mixture, and I did not appear to get those tiny circles. It is hard to say what caused them, but the little boards were bad designs anyway.
The painted large board was of noticeably worse quality than the vinyl one. I think it may be because I used a solvent based paint, but I'm not sure. For the hassle it was worth, I prefer to stick with just plain vinyl. It appears to produce very good results, and I saw no over-etching anywhere on the vinyl board. Vinyl also peels off, unlike toner or paint, which means a brighter board in the end. The toner or paint will stain the board when you use a solvent like acetone to remove them.
Once your board is all etched, drill your holes for your components (If they are through-hole) and assemble your board!
If you have any questions, feel free to ask! I will answer them as soon as I can.
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