2-Layered PCB with a Laser? Nah, Toner Transfer

I tried using the laser to remove some spray paint, and... I declare it a dud. Two major factors stymied this process for me for the moment:

1. I didn't have the right spray paint (matte black) nor the right environment (dry and warm) for the paint I did have. What I did get to stick to the copper had a very uneven surface.
2. The laser is... finicky. I can't tell if the layers were wildly inconsistent, if the paint behaved differently as it dried, or if maybe the laser had trouble, not liking the cold temperature or moist environment. I never can tell if it's about to give up.

Impatient as usual, I used my regular method: laser printer toner transfer. Determined to make a 2-sided board work, I spent a while aligning corner crop marks and pre-taping the paper with the toner before laminating it to the copper. The toner transfer worked beautifully-- perfect result laminating it ten times (5 up, 5 down), but the top-bottom alignment, while close, may not be close enough. At this point it's etched (see photo) and drilled, but there are still bridges and the misalignment will make assembly an adventure.

Looking at guides online, (especially the tutorial at An Engineer's Life which so many people are linking to today,) it does seem like most people use a photographic process and abandon toner transfer when they go for double-sided and SMD. Before going that route, I want to take toner transfer further though-- I've had such good results so far, the only issue is top-bottom alignment. The biggest sources of alignment error:

1. Top-bottom alignment of printed out patterns. A light box, some magnets, and tape should do the trick-- I need to see the registration targets better. Update: lightbox on the way from B&H.
2. The laminator binds and jerks sometimes, which could distort the pattern slightly. It's hard to tell without sending through a test image, but it seems like time to take apart the laminator and see about modding it to separate the rollers a hair.

I'm happy with a slightly lower level of quality with toner transfer because it's a simpler process with fewer (and cheaper) expendables that can also transfer labeling to the top and bottom after etching.

MinimalDuino 107 Pattern

After submitting the 105c version to the DorkbotPDX PCB order, I mentioned I'd make one at home, but the traces looked so thin on paper and I didn't like the routing of gnd to the crystal area, so I made a few changes to optimize it for toner transfer and home etching.

Here's a shared folder with the updated, v107 EAGLE files and a 600dpi jpeg for toner transfer. See the low res at right, or click for higher res; get the full res jpeg here.

Alarm Clock Board Built!

Last night, I finished the board layout in EAGLE and got to work making it:

• Turned off layers in EAGLE except layer 1 and pads, and printed to a PDF,
• Rasterized PDF in Photoshop at 1200dpi and processed into a black+white image (right),
• Laser printed onto an L.L. Bean catalog page, with the print output set to "transparency,"
• Ironed onto 2.5" x 2.2" single-sided copper clad,
• Fixed gaps with etch-resist pen,
• Rubbed off paper and etched in ferric chloride for 15 minutes (though I'll use use the HCL and peroxide method in the future),
• Rubbed away ink with acetone,
• Tested trace continuity and scraped away tiny bridges with a knife,
• Drilled out all holes (1mm bit),
• Populated with parts and soldered it up,

• Pressed chips into sockets,
• Hooked up LCD, jog/shuttle, a button and LED.

It behaved exactly like it did on the breadboard! Now I can focus on the right button/LED combo and casing, redoing the relay board, and tightening up the program.

This is my first from-scratch Arduino-compatible board-- sure to be the first of many...:)