Saturday, September 20, 2014

Home-Etched Circuit Boards - First Try

I've done a good bit of messing around with hobby electronics: BASIC Stamp when I was in 4th grade, some Arduino during middle school, down to the more obscure Axon II and plain bare-bones Atmel boards that you had to solder up and use an AVR serial programmer with. Its a whole lot easier to have fun with microcontrollers now that Arduino is in the spotlight. Regardless, I had always wanted to make my own circuit boards, the stuff was expensive to me at the time and guides always said you needed a laser printer, which I didn't have at the house. I decided it was time to finally get my feet wet designing and manufacturing my own printed circuit boards!

As I stated above I don't have easy access to a laser printer so my first challenge was coming up with some way to sufficiently protect the copper traces I wanted on the bare board so they could survive the etching process. I really didn't want to pursue the laser printer route because that would mean having to access a computer during school and print something out, and I couldn't choose what paper it was on. If I made some mistake or needed another one I'd have to wait at least a day to print again as well. Another option was this photo-resist compound with a transparency to control what parts of the coating on the bare board were exposed to the UV light. This meant a lot of extra components in the etching process as well as more money and time. I did know however that simply drawing on the boards with a sharpie works well if you do it correctly. This meant that if I could just draw really accurately all I needed was a marker to make the traces on the board. All I needed was something that was computer controlled, moves in 2 axes, and could hold a marker. I had one of these—a 3D Printer.

I didn't want to spend time printing out a mounting bracket for something that might not pan out so a few zip-ties later and I had a sharpie sufficiently mounted to the extruder on the printer.

Sorry about the photo, I had to hold my
camera from the top and hang it
behind the printer

Yeah, its really shoddy, but for some tests it worked just fine. There is pretty much no force on the pen while its drawing.

The next problem, and this was a big one, was how to convert my vector graphics of the board traces into something the printer would understand. Turns out there is pretty much no documentation on how to actually do this. I finally figured something out that I liked and I'll go over it briefly here. I might make a video about it since this should be documented out there and it took far to long for something this simple.

First I took my vector drawing of the traces (.dxf from Eagle or .svg from Fritzing) and opened it up in Illustrator (I'm sure any editor that can work with the files would work). In this I cleaned it all up, which generally just meant joining all of the paths into one shape. This may not have been necessary but I wanted to make sure the file was as easy to use as it could be for the next step. Next I opened up the Illustrator file in Inkscape.

Here's where I kinda cheat at making the printer plot my traces. Instead of going though all of the trouble to convert these paths into gcode in a nonstandard way, I'm just going to trick the printer into thinking its making a 3D object. It's just a really really thin object.

After getting the OpenSCAD Extension for Inkscape I exported the path as an OpenSCAD file and specified a height of .1mm to it. Going into OpenSCAD I opened the file and exported a .stl from it. I now fed this into my slicing program of choice, KISSlicer, and played around with the settings a bit. I set my extrusion width to the width the pen draws and set the extrusion multiplier to zero. This means it wont actually run the extruder while it draws the circuits.  I then set my layer height to .1mm, matching the height of my .stl file. This means it will only draw the design once and not move upwards (off the board) and try to draw again.

Finally and very importantly I set the slicer to perform a large Z-lift while drawing. This means it will actually lift the marker off the board, lower, and move once it is drawing another part of the path. If I didn't do this there would be marks whenever the marker moved to a new starting point of a line, a move where the printer would choose not to extrude if it were printing an object. I had to do some manual changes to the gcode too, like removing the heat up bed and nozzle statements as I couldn't figure out a change to that in the slicer.

Now I opened the gcode in Pronterface and printed away. Of course I had to properly zero the z-axis for the lower pen, getting the depression of the tip just right. I had a used marker, but I still got fairly thin lines. I imagine with a new one it would work much better.

Now to etch the thing. I instantly thought Ferric chloride, but that you could only get in 1 liter bottles from a select few Radioshacks around here and besides, it got used up after a while. Besides, it comes pre-made, who wants that when there's a DIY alternative! And then comes the homemade etchant of choice: HCl + H2O2 Now that's a real etchant! H2O2 is just hydrogen peroxide, we have some of that right now. Next is HCl, and after taking AP Chem I felt reasonably confidant in handling the acid and taking all the necessary safety precautions. I thought it would be hard to obtain however since HCl is some bad stuff; you can hurt yourself pretty easily with it. Almost scarily, it isn't though. And it's in high concentration.

Trip to Lowes and CVS worked out well

Behold, Muriatic acid. Sold to clean brick and control pH levels in a pool this stuff is a whopping 10M. To put that in perspective once you get to ~12M the HCl starts to diffuse out of the solution as HCl gas. Metal dissolving and flesh burning GAS. If you thought it was bad in liquid form imagine having it in the air. You don't mess with this stuff, and if you get this on you, its really gonna burn. Not to mention I have no doubt the fumes of it are bad for you, and you can easily smell it when you open the bottle, so doing this outside I think its a must. There was a breeze and I still had to step back a few times.

I won't go though the mixing and etching process now because there are many other good guides on making this etchant. I liked NurdRage's segment on this in Make 10 Etchants for PCBs.

After a test etch with some stuff I drew by hand on a board came out reasonably well I decided to run my computer plotted circuit though the etchant. The ink was on thicker this time too so I figured it would withstand even better than the test board. I wanted a simple little circuit first, so I just wired some LEDs up to a male header. Unfortunately I don't have a proper PCB drill yet so I had to use something that was three times to big. Not surprisingly it made the soldering come out horribly, but hey, it worked. Trust me my soldering is never that horrible when I'm not trying to bridge huge gaps.

My cutting technique needs a little work

Wow that soldering is embarrassing

This project was really just meant to set me up with a new skill for future use where I need to make my own circuits. I now have a new technique in my arsenal. See ya plastic proto-boards!

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