Tuesday, January 25, 2011

From Cricut, to Circuit - Part II - Etching Your Circuit

7. Prepare layout for etching - The first attempt of this was to see what would actually happen when I dropped the board into the Ferric Chloride. What came out was some mixed results. the pattern was etched as expected, but there were some unwanted side effects with the process. There was a slight amount of undercutting underneath the Vinyl, which caused a bevel at the edges of the copper traces. there were some spots under the Vinyl Where the FeCl had gone completely underneath the vinyl. Not perfect results, but perhaps still usable with some tinning. The most interesting part was where the Sharpie marker had hit the edges of the Vinyl. There was almost a perfect edge at those spots. (circled in red)

By this point, I had also just discovered that the ValveCaster board I etched was missing a specific component (by the layout creator's design) and probably wouldn't be as useful as I wanted...

However, this was great for an experiment, and I learned a lot from this, but I was ready to try a different tactic...I took another layout for my 2nd attempt, this time for the Pepper Shredder pedal, which is more involved and intricate. Taking another layout:

And converting it into another SVG cutting path:

Cut it out, and applied it, and etched it. I missed the step this time of pressing it with a iron, so the undercutting was more extensive than the first one, with it going almost 1 millimeter under the vinyl.

Not pictured is where I followed another's advice and marked out large sections of the copper board with sharpie, to conserve Ferric Chloride. There was one point where I had used a piece of paper as a straight-edge and marked across the board, between the intended patters, as a separator. Well, there was some ink-crawl underneath the paper and the sharpie ink hit the vinyl again. After wiping it off with Isopropyl Alcohol I discovered on etching that where the Sharpie ink hit the vinyl again, there was almost a perfect edge to the copper traces. Maybe I was on to something here. Time for a 3rd attempt...

I cut out another set of patterns on the Cricut in Vinyl, and applied it to another Copper board. This time, I liberally applied a wet sharpie to all the edges of the vinyl to see what result I would get this time:

I then thoroughly wiped off the entire board with Alcohol to remove the Sharpie ink on the surface. After running it through the etch, I discovered this was the secret to get minimal undercutting, although it presented another issue of its own. Be sure to remove ALL extra sharpie ink off the surface, or you may find yourself with short-circuits (which are easily cut and can be scraped off an Exacto knife)

(click for full-size)

Monday, January 24, 2011

From Cricut, to Circuit - Part I - Making a layout

1. I have found a few layouts that other people have done on various sites, and through GIS. I selected a few to work with and first tried on a ValveCaster pedal design by Freekmagnet from DIYStompboxes.

2. I imported this into InkScape and created another layer on top of the image to draw a path on. First I started drawing boxes for each copper bus, and circles for the pads, but kept getting SCAL to make unwanted cuts through the pattern. I discovered that I would have to use the pen tool instead of the shapes tool to draw around the entire pattern to get a workable layout without any extra cutting through the entire layout.

3. I imported this into SCAL, and prepared to cut out the design by making copies of the image, and placed multiples across the page.

4. I then examined the cutout to make sure that it matched the SVG I created. So far so good.

5. I then cut 110# Cardstock on the Cricut to test the cutting pattern.

6. At this point I ran into several failures in trying to get the layout transferred onto the copper. I tried to mark it with an Industrial Sharpie marker, an MG Chemicals Etch-Resist pen (also a branded Sharpie marker), even Enamel spray paint. All of these methods proved that the paper absorbs too much, and bleeds through making a really, really messy transfer.

I received a suggestion from two independent sources to use adhesive backed stencil material. Cricut sells this stuff at any craft store, or you can find it on the cheap at the right hardware stores.

I tried it out and got much different results in getting a workable transfer onto the copper. I applied a section of Cricut Transfer Tape to the top of the Vinyl cutout, removed the backing on the Vinyl, and applied it to the copper, thoroughly pressing it down with the included applicator stick and then with a warm iron. I then SLOWLY removed the vinyl from the copper. The transferred pattern turned out very clean, and on the first try I got a 90% transfer rate, only losing one layout to a missing trace, which I then promptly scratched out with a fine-tip Sharpie since it was unusable.

Then things became interesting once I dropped this board into the Ferric Chloride bath....

From Cricut, to Circuit - Preface - Making your own circuit boards

I Cross-posted this to the DIYStompbox crowd, and got some interesting feedback. It has been a few weeks since I wrote about this here (or anything for that matter), but I have developed a working process in that time. I have been pleased to get some satisfactory results with much trial-and-error. First things first:

The required software:
1. Download the Cricut DesignStudio (Trial Version) - Required to update the Firmware of the Cricut Personal from v1.0 to v1.34.
2. Download for free - Inkscape - to convert popular Raster graphics formats into SVG Vector format
3. Obtain Craft Edge-Sure Cuts A Lot - To cut/draw TrueType Fonts and/or SVG files

The Process:
1. Create a custom PCB layout, or download your target layout created by someone else. Some people prefer to use full-fledged design software like AutoCAD, but there are other tools out there more specialized for Electronics production, like Storm Software's DIY Layout Creator (Java Required)
2. Convert PNG, JPEG, GIF layout into SVG using InkScape
3. Import SVG into Sure Cuts A Lot
4. Verify paths are clean, and do not cut across your traces in a continuous fashion (I may need to write another tutorial for this in InkScape, with the best practices I have found.
5. Cut Layout pattern with Cricut
6. Apply cut pattern to Copper-clad epoxy board
7. Prepare layout for etching
8. Etch your board in an etching solution (Ferric Chloride, Sodium Persulfate, Ammonium Persulfate)
9. Process the etched board (cleaning, cutting, drilling, tinning, etc.)
10. Post-production

Saturday, January 8, 2011

Printed Circuit Board challenge, using an ordinary Cricut

I love making electronic hardware, I have been only at it for under 3 years but it is a rewarding hobby. I sometimes worry about the reliability of the things though if I ever decide to get into the manufacturing business and selling my creations. I have been researching different ways to do up printed circuit boards to give my amps and pedals more reliability and durability.

For Christmas, the wife and I were given a used Cricut by the parents. It was due to them upgrading to the next larger model, but I have been thinking of other ways to use it besides cutting and/or drawing on paper/vinyl/foam, it's intended use. Now scrapbookers have quite a community for the Cricut but they are constrained by the cost of the $80 font cartridges that are required for the Cricut to operate.

Looking around on Youtube revealed some interesting things, namely 3rd party software out there that does not require the use of the expensive cartridges to operate the thing. One software package, Sure-Cuts-A-Lot, eliminates the requirement of the cartridges altogether, and allows you to 'print' TrueType fonts and custom layouts using the Scaled Vector Graphics (SVG) format directly through the USB port. Another is to flash the Firmware which will open up the device completely and allows you full control of the steppers and solenoids, the Open Source FreeCut (GPL), but this will obviously void the warranty, as there is no way to reflash the original Firmware back onto the device. This thing is a hacker's dream to turn it into a general purpose CNC machine.

My challenge has been figuring out how to either physically cut out a Copper-clad Garolite G-10 epoxy board into traces, quickly and easily without destroying the Cricut itself. This will cost a lot of blades to do this...or an even better solution is to get my hands on the pen-holder and find an etch-resist pen that will fit it, that I can draw out a mask and drop the printed board in Ferric Chloride and etch away the exposed copper.

Unfortunately the form-factor of the Cricut only allows miniature pens and markers...and no pen-manufacturer produces a miniature industrial-grade marker that can withstand Ferric Chloride or other etching agents. I could probably disassemble the Cricut and give the carriage more head-room by removing the keyboard assembly to allow for full-size etch-resist pens to fit...or I could hack and replace the guts of a mini marker with the industrial grade ink, to fit the Cricut without modding it.

More on this as I come up with more info...and Pics and video will be included as the project unfolds.