I tested a few different etch-resists over the weekend with good luck, but the process itself still needs improvement before the boards will be usable.
The three resists I tried were Johnson "One-Step No Buff" floor wax, Krylon purple spray paint, and black Lacquer spray paint.
I made three test pieces of PCB material, one using each coating, then scratched each one manually with a nail, and etched. The wax was applied by pouring a thin stream over the top of the metal and propping it up at an angle on a paper towel to let the excess run off.
After etching, the floor wax was a clear failure, the coating was just too thin and failed over about half the surface. The purple Krylon seems like it worked well, as did the black Lacquer. Clear paint looks awesome but its hard to tell when you've sprayed enough on.
Also, one thicker coat seems to work better than two thin coats like you might normally use.
I still have a couple of problems to solve before the process will be more useful however: I need a wider scratch mark, and there's an annoying jitter in the tool during the first quarter or third inch of motion on the X-axis.
After making the test pieces, I scratched a full-size test piece using the matte black Lacquer.
Edit: Unfortunately, the etched scratches still do not completely separate the areas of copper, resulting in 100% shortage across the board surface.
Clearly I need to find a better resist and tool usage combination. The fine parallel lines still resolve clearly, but are also not fully clean. They are also not close enough to merge when etched. I think a softer resist might be desirable, so now I'm thinking .. what about melting a very thin layer of candle wax onto the surface with a hair dryer and then scratch wax but not metal with something pointy but not sharp, like a tooth pick?
Also, much hotter etchant may work better as well (this most recent board was done at room temperature and appears to be incompletely etched before the resist started to fade. Previously I used a double ziplock bag with a few TSP of etchant in a hot water bath with good results.
I've been trying to learn all I can about the Cricut hardware and its potential for upgrades and alterations.
Last night I completely disassembled my Cricut Create and took closeup photos of the circuitry. Then, I realized I could completely extract the metal "working" parts of the machine and reassemble outside of the shell. This allows much greater access and room for potential modifications.
At some point I'll build some kind of new "open air" case to display the guts in working condition rather than try to stuff it back in the old case.
Found a great looking how-to on designing multilayer stencils using the "threshold" filter in Photoshop & Illustrator. I think this could also be done in Gimp.
I've created this writeup on my current Cricut PCB process, and posted to the hackerspace Wiki.
I make PCBs on the Cricut by the following process:
1. Design a one-sided board in Eagle. Export the trace and pad layers only to a monochrome PNG file. 150 dpi seems to work well so far.
2. Using GIMP, add a fine outline around all traces.
- select the entire background color (black) with the "Select by Color Tool". - Do a "Select->Shrink" and shrink the selection by 1 pixel. - Fill the entire selection with the trace color (white) using the Bucket Fill tool. Make sure you have "Fill whole selection" set. - "Select->Shrink" by 1 pixel again. - Fill the entire selection with the background color (black). - Finally, save out your image as a PNG file.
3. Import the GIMP image into whatever software you are using to drive the Cricut (such as Make-the-Cut). In Make-the-Cut, I use the following settings for the highest accuracy tracing: Threshold 180, Resample x5, Smoothing 0, Optimize 0. If you use a PNG image it should import to the correct size. I have had trouble with other image formats becoming larger or smaller when importing.
4. I highly recommend using a fine-point pen tool to draw a preview test of your design on paper to check for sizing and other issues before potentially ruining expensive copper.
5. Prepare your PCB material. I am currently using super thin 0.015 single sided FR4, but the machine should be able to handle thicker materials, as long as your tool holder and tool can still clear the work piece. For an etch resist, I put on a single thick coating of spray paint as my etch resist, but plan to try Future floor wax next.
Information about using Future floor wax as etch resist.
5. Load some kind of "scratching" tool in the Cricut. My current preference is a deck screw or a sharpened nail. (The scribing tool is a bit too fine and can result in bridging). You can use a custom tool holder or just masking or packing or other "hard" tape. Pay careful attention and set the installed height of the tool high enough to make sure it won't drag across your work piece while "up".
6. Finally, use the Cricut to scratch your design into the prepared PCB, and etch. I have been experimenting with different settings for pressure and multicut, but currently I like "high" pressure, multicut x2.
Here's something I did a long time ago, then re-implemented last fall for Java.. It's an updated version of the old "galaxy" screensaver mode from xlockmore, using the Sun "SaverBeans" API.
My version makes the star color change according to its speed, from dark red for slow, to orange, yellow, green, and blue for the fastest. It also makes the star sizes variable so they're not all just single pixels like in the original version. I find it pretty mesmerizing.
I had actually submitted these changes to xlockmore way back in 1997 but somehow they got removed at some point.
I've exported the Eclipse project so you can build it yourself if you want, there are a few settings that affect speed, number of stars, star size range, gravity constant and such, but I never bothered to implement a "settings" dialog so you need to recompile it to play with them. I just fiddled with it until I found something that worked well on my machine and left it alone after that.
If you run the "debug" target in the included ant script it will instead run the saver in a window.
If you just want to run it as a real screensaver (and you trust me), there's a zipfile inside called "galaxy-win32.zip" that contains the necessary files and a readme that explains how to install (basically, copy the 3 files into your c:windowssystem32 folder and check your screensavers)
One of the first things it seems like every interested hacker asks me about the Cricut is, "how can we get it to do PCBs?" Well, I've finally done it!
I created a single-sided circuit design in Eagle, using 50 mil traces, then exported just the pads and traces as a monochrome PNG file.
Next, I sprayed a coat of clear spraypaint on some single-sided 0.01" PCB material and let it dry well. (Next time I will use two coats)
Finally, I imported my design into MTC using pixel trace and used my scribing tool to scratch the design onto the PCB (multicut 2, pressure high). This removed the spray paint around the edges of my traces. After it was done, I used a toothbrush to brush the removed-paint-bits off the board.
Finally, I etched with a few tablespoons of ferric chloride in a double-bagged-ziplock immersed in hot water. The whole etching process took less than ten minutes. Aside from some unwanted specks where my one coat of spray paint was a bit light, the result looks perfect!
Obviously I still have to do more work to make this board functional, I'll report back when I have more to show.
EDIT 3/13: I tried drilling the board and soldering up one of the oscillators, and it turned out that there were a couple of shorts in my etched diagonal lines where some "jaggies" were really close together. Also I discovered that the "donuts" need to be larger in diameter to leave more solder pad remaining after drilling the hole, especially the ones for the 555 chip.
I discovered several of the gel pen colors in my set are brightly fluorescent.
This is an intriguing looking option for etch stencils.. Check out the Dura-Film process here, which uses a UV light to expose a film that washes away in developer. I can't tell if the stencil disappears completely or if it leaves a mesh in the open spaces like the Riso film.
The biggest downside is the extreme cost of the stencil sheets, several dollars per 8"x10" sheet.
I fixed my third Cricut this evening, an Expression that I got for $15.50 on eBay in mid-February, sold as defective.
When powered on, the carriage would go all the way to the right, crash into the right end of the track, and make a nasty noise for several seconds as it kept trying to continue past the end. I suspected that the "home" button in the carriage's hidey hole had some problem.
I removed the right side cover (by popping off the silvery ring part and gaining access to screws around the perimeter of the cover), and discovered one of the two limit switch wires had simply fallen out of the switch guts. I simply pushed the wire back securely into the switch and the machine now started and self-tested successfully.
The hamsa was done after a suggestion by Brooke.