Last Friday I needed to evaluate the Motorola MC33926 motor driver chip for my Brightleaf
tracker design. The Pololu carrier
arrived and its time to wire it up. Normally I close the door and commense to soldering. I looked over the amount of work and decided upon a custom circuit board. I've used 4PCB's Bare Bones
and itead's prototyping service
with great success. But I want it working now! Time to etch
I whipped up this little circuit in eagle
. Its a simple Arduino shield
with some connectors, resistors and caps.
I only had single sided copper cladded circuit boards, so the layout was restricted to one side. I opted for the bottom side because the connectors are thru-hole parts on the component side. Hope that makes sense.
I didn't use an clothes iron because I borrowed a Vulcanizer
. (Insert your Spock jokes here.) So if you didn't read the links above, here a summary. Using shiny coated catalog paper in your laser printer, you can transfer toner (the board layout traces) to the shiny paper, but the toner doesn't stick well. Smash the printed shiny paper onto the copper board then apply heat. The toner will transfer to the copper and make a great bond.
Plop into hot water to dissolve the paper and you're left with a copper board ready to etch. Hmmm, well not yet. My first attempt failed, the Vulcanizer wasn't hot enough, the toner didn't completely bond to the copper.
Board #2 looks better, a few problems that are fixable with a Sharpie. I scrapped this one also, then made board #3, it was perfect. Well almost, The artwork was mirrored, then applied. Mirroring the bottom side artwork was incorrect. I fussed for about 15 minutes to create the correct artwork then made board #4. Isn't 4 a charm?
Oh yeah, look at that baby.
Now that's some close traces. Time to etch.
I stopped making PCBs years ago because I hated dealing with Ferric Chloride, nasty nasty stuff. Last night I read about folks using 1 part Muriatic Acid to 2 parts Hydrogen Peroxide as etchant. If this guy can do a 100 pin TQFP
at home then I got to try it. After 10 minutes of etching, I'm left with this. All the copper has gone away, the toner protected traces and pads remain. The etching would have been faster but it was cold in the lab. I seem to remember something about chemical reactions and heat, but Mr Bergquist's 10th grade chem class was a long 32 years ago.
Here's what the birdie sees.
I removed the toner with some acetone and I now have a shiny new board.
There's a little bridging here, I'll fix this with a razor blade.
But not here, its' looking good.
I didn't quite make my first board in an hour but I'm a happy man. Little boards like this will save me hours of hand wiring. If I stick with surface mount parts only, I'll be kicking it with new designs every week.
Look Ma, still pushing electrons after all these years!