Etching Your Own PCBs

   I decided to have a go at etching my own PCB.  It looks like it will be a while before I get around to building my CNC router, so I thought I'd give a thought to making boards the chemical way.  I've been a bit put off by the idea of having strong acids in the house, so I never got around to trying this.  As luck would have it, I've been following Quinn Dunki's "Blondie Hacks" blog for a bit, watching her develop her own computer from scratch.  She posted a blog, detailing her PCB making process.  I was surprised to find that she does her etching with Hydrogen Peroxide, White Vinegar, and Salt.  That sounded a lot safer than HCL!  I checked with my wife ( a chemistry ( and physics, and calculus ) teacher ).  She gave me the basics of the chemistry and seemed to think it would work.  Here's what happened.

   First, I read Quinn's blog about a hundred times.  She links to the Sparkfun tutorials about EagleSoft CAD.  These are the same tutorials I had used to get started.  They are excellent, and Eagle is free ( as in beer ).  She also has links to most of the materials you will need.  I got alot of stuff from the dollar store ( peroxide, acetone, tupperware, foam brushes, picture frame, cotton balls, funnel, etc ).  I was ordering from mouser.com anyway, so I got my presensitized PCB and Positive Developer there.  I can't say enough good things about mouser.  Once you get used to their search filters, you can find almost anything there. 

   I have to take a detour here and talk about mouser a bit more.  I thought their shipping prices were a bit high.  Then, I got my package.  I had ordered some new microcontrollers, some SOJ SRAM, some 74HC logic chips, and other stuff with my PCB and developer.  Wow!  I thought they were delivering medical supplies.  The careful packaging, the anti-static bubble wrap, all kind of blew me away.  The craziest was the packaging on the SRAM.  It came in an anti-static silver baggy, of course.  On that was the usual yellow warning label that this was a static sensitive device.  In addition was a label that looked like the instructions for handling an human organ tranfer.  We're talking about expiration times, humidity controls, temperature controls; you name it.  Inside the bag ( once I got the courage to open it ), I found 3 silica gel packs and a Ph sensor card along with a small black box.  The box had additional warning and control information.  Inside the box, in tons of carefully arranged anti-static foam, were my two little SRAMs.  Did I mention that everything was in English?  And most of the entries were hand written.  I was very impressed.

   Anyway, back to board etching.  I decided to start with a simple board.  I got a new Pic18F4550 and decided to make a carrier board for it.  First up was the schematic in Eagle:

   From this, I made a board, following Quinn's advice on hole size, ground plane, etc.  I won't repeat everything she says.  Go read her blog.  It's well done.  Here's the board:

Nice and simple, and it won't need any jumpers.  I did forget to add in the decoupling cap though. Doh!

   From there, I printed the board as a PDF file and edited it with GIMP.  I printed this board along with the next one I'll try ( line follower sensor ) on acetate.  I found some HP transparencies that work with an inkjet printer.  They have a rough texture on the printing side that helps absorb and hold the ink.  They dry quickly and come out very dark:

   Still, I doubled them up as Quinn suggests.  This seems to have made a difference.  Taping them together wasn't as much of a pain as I thought it would be:

   Then, it was on to the darkroom.  I used my basement workshop/office.  Luckily, I have a ton of red LEDs sitting around down there.  I threw ten on my breadboard to use as a darkroom light:

   It was dark, but it did the job.  I had a bit of trouble when I put the board onto the glass.  It was tough to see if the board was aligned with the artwork.  For no particular reason, here are the LEDs on:

Behind the LEDs, you can see the bench power supply I made from an old PC PSU.  I forgot to blog that one up as I did it.  Oh, well.  It's great.  Right now, It supplies 12, 5, and 3.3V with plenty of amps.  Here's the board under exposure:

   Here's the developer bath all ready to go.  I didn't have time or light to take pictures here.

   Behind the tupperware, you can see my three new stepper motors.  I hope to use them to build my CNC.  They're going to be too slow, but they should work.  Also, to the left, you can see the proto board for the line sensor and my robot behind it.  To the right, you can see a bunch of new chips I got from Mouser.

   After developing and a quick rinse, it was on to the garage for etching.  I mixed equal parts of hydrogen peroxide and vinegar.  The etching was *really* slow.  I'm glad I brought along a healthy cup of salt.  The salt acts as a catalyst for the reaction.  I think my tupperware is too small.  Next time, I'll use a bigger one to speed up the reaction.  Here's the board just dropped in the etchant:

   And here is the final product:

   I left the resist on for now.  I'm waiting for my drill bits to arrive.  With luck, I won't peel off too many pads!