Felix, in your excellent video on etching aluminum soda cans to produce solder paste stencils, you talk about your etching solution, 1:3 muratic acid/hydrogen peroxide (or is it 3:1). My questions are:
What volume of liquid do you use for you use for a 'batch' of stencils (assuming Moteino sized boards)?
Are you able to reuse the etching solution for more than one batch?
If so, how many batches and/or time does the solution last before you need to make a new batch?
Thanks in advance,
Tom
Tom,
Honestly - I have used a single mix in my entire soda-can stencil etching experience. I still have that bin in my lab. I kept adding a bit of acid and a bit of hydrogen peroxide, probably 2-3 times since the original mix was made. I have probably etched 40-50 small prototyping stencils in it.
The total amount is probably around 8 ounce or so.
The solution is 1:3 acid:peroxide.
I have since switched to laser etching my stencils which goes a magnitude faster, probably 1 minute of actual etch time for a small stencil, maybe 15-20 minutes for a very large panel stencil.
The advantage with laser etching is i'm not limited to the amount of aluminum I can cut out of a can, also chemically etching implies a near-perfect toner transfer on a larger surface which is harder to get. If you have access to a laser cutter, I strongly recommend this method instead. If you're on a budget and have about 20-30 minutes to spare, the soda-can stencil method works a treat once you get the hang of it.
The original soda-can stencil tutorial is here: http://lowpowerlab.com/blog/2013/02/11/diy-smd-metal-stencils-the-definitive-tutorial/
I've just tried for the first time toner transfer method etching.
First of all, tutorial is excellent and I was able to follow it easily :)
I did completely failed on my first try tho, and was wondering if you have any suggestions.
I encountered 2 big issues:
1. I actually bought special toner transfer (yellow) paper (since I couldn't find vinyl liner) and it kind of worked, but I still had small pieces of toner that didn't get transferred to aluminum. So I used a sharpie to paint over (I only had blue color). That's where first failure came from, acid completely ignored sharpie paint, and etched right thru it :( So what kind of marker did you use in your project?
2. I did exact 1:3 mix, but it seemed very weak. It took me about 45 minutes to etch. Large pads came thru in about 15 minutes, but smaller QFP pads didn't etch at the same time. Result was ugly :)
I suspect reaction time was also slow because solution was kind of cold, I might try warming it up next time, and maybe used 1:2 ratio...
Other minor issues I've see is that cans that I used were not the best, and it took me about an hour to wipe off coating with Acetone... I'm gonna try other brands (so far I tried diet coke and Starbucks energy+coffee). Oh and is it important to wipe off graphics and coating from the other side of the aluminum? I thought it didn't matter since it's covered by tape anyway...
I also cropped image too close to the pads and in result I couldn't cover edges with tape close enough (again I used marker which didn't work), so next time I'll leave bigger border. Lesson learned :)
Finally when acid was eating away metal, it formed very large bubbles above each pad, and piece kept floating up. I have no idea why it happens, in your video you get a stream of fun tiny bubbles :)
Happy to hear that using laser cutter now! I also ordered one. I assume you use plastic film for stencil or can you actually cut aluminum on it?
And I actually found answer to my 1st question. Its marker's color. Blue sharpie let's acid thru, black doesn't. I went out and got 2 black markers one made by Sharpie, and one by Bic. Both held up to acid test...
The mix is something you also have to get right. The acid I used is muriatic (hydrochloric acid) and is 30%, from home depot. I mixed that with H2O2 from the pharmacy, all very cheap. So that gave me a very strong mix that I never ever had to throw away, I just kept adding tiny bit of acid to rejuvenate it. I never even warmed it up and it would always take from 5-10 minutes to etch the soda can aluminum. I made many many stencils with that method. The hardest part was the toner transfer. The best method to get a very good transfer was with the vinyl, that was the best. The next hardest thing was to get the interior epoxy protection film off the aluminum without scratching it, so that the toner would stick to the pure aluminum surface, scratches would make that impossible. For that I would heat up the aluminum under the clothes iron for a few minutes, that makes the epoxy easy to remove with acetone from home depot, you may try paint thinner as well. After that the toner will transfer easily from the vinyl.
THese days I etch my stencils with my laser cutter, from mylar transparencies, also very cheap and very fast. It's perfect for prototyping. For production of all my panels I order stainless steel stencils. I actually laser etched a full panel in a mylar sheet once and I was pretty happy with how it performed, but the bigger the panel the harder it is to keep the mylar stable on one side when applying paste on another side.
Thanks Felix! I'll try different mix ratio. I feel like a homeless guy, looking for empty soda cans everywhere :) Still haven't perfect one... I was actually thinking of using polishing wheel attachment for my drill press (or bench grinder) to take off epoxy. I used it before to polish aluminum parts (external spacers) of my Xronos clocks.