With a little practice, you can make excellent double-sided PCBs by combining a laser cutter with chemical etching. The basic idea is: the laser cutter blasts away spray painted etch resist, then chemicals eat away the exposed copper. Once the copper is gone, the underlying board can be cut again with the laser to make through-holes. No drilling required! After some setup and practice, you should get reliable boards with 8-mil trace/space and hundreds of holes in about 2 hours. You can even cut internal routing and odd board-shapes!
You'd never want to make a bunch of boards this way, but if you want a same-day prototype of a new design it's perfect. I love this process because I don't have to wait 2 weeks for boards to come back from fab, so I can design aggressively and try new ideas. If you're in a research lab or shop you'll have no trouble finding the materials, but you should also be able to find everything you need at a hardware store and pharmacy.
This Instructable will go step-by-step through the process of making a double-sided board, with special attention paid to using software to generate a good laser path, and some neat tricks to help get good alignment between the top and bottom sides of the board. Drop me a note if you've got feedback or new ideas!
The steps are:
(1) Coat PCB stock with spray paint
(2) Laser cut a spring-form alignment jig
(3) Optimize your board layout for fabrication
(4) Generate vector art for the cutter
(5) Etch away black spray paint with the laser on both sides
(6) Chemically etch away exposed copper
(7) Laser cut through-holes in the exposed board
(8) Tricks and tips for soldering DIY boards
Stuff you'll need:
Access to a laser cutter
FR1 PCB blanks (try www.inventables.com)
Spray paint (McMaster #7719T9)
6"x6" of acrylic between 1/8" and 1/4" thick (3 mm - 6 mm) for making a jig
Drill press or rotary tool with small bit (optional, but helpful for alignment)
Non-metallic dish, measuring device, and tools
Hydrogen peroxide (3%)
Hydrochloric acid (30-37%, also called muratic acid)
You'll also need some access to software:
A PCB design, exported to a format your graphics program can read (I use Eagle exporting to EPS)
A vector graphics program to edit the art in. I used Adobe Illustrator.
A brief note on safety and the environment:
If you have access to a laser cutter you should be familiar with the dangers involved with that. But these instructions also guide you through copper chloride etching, which you may not be familiar with. The chemicals used are dangerous. Hydrochloric acid can burn your skin, blind you, and generates poisonous fumes. The hydrogen peroxide is reactive with lots of stuff, and the heavy metals (copper) are poisonous. Always work outside (or in a chemical fume hood), in gloves and goggles. And make sure you have adult supervision if you're under the age of, say, 40.
Finally don't put your etch waste down the drain - it will poison both people and the environment. Store it safely in a labelled container, and dispose of it properly by contacting a hazardous waste disposal agency in your area.
Lots of people have previously documented parts of this process in some detail. I'm a huge fan of:
You should check these out.
Alright. Let's get started!
First, you'll need to acquire some PCB blanks. I've found that FR1 (a paper and resin based stock) laser cuts much more reliably (and without noxious fumes) than the conventional fiberglass FR4. This is critical if you want to generate through-holes or board edge routing. You can purchase FR1 copper-clad in both single- and double-sided flavors at http://www.inventables.com.
Next you'll need to coat the stock on both sides with spray paint. I've had good luck with Rustoleum Flat Black (McMaster #7719T9). Go for the thinnest coat you can get that reliably coats the whole board, and error on the side of not enough paint (you can do touch-ups with a Sharpie marker later). Thin paint is important because when you blast the paint off with the laser a thin film of it will resettle. The thinner the paint layer you blast away, the less there is to resettle. Keep the spray nozzle at least 18 inches from the boards to get a light and even coat.
(BTW, I've tried a few other spray coatings - one acrylic based, and one epoxy based - to find something that didn't leave an etch resisting mist. But the flat black seemed to work the best.)
Allow about 15 minutes for the top-side paint to dry before flipping the board. Try to keep the paint on the back-side the same thickness, or else the two sides of the board may etch at different rates.
Spray painting is messy, so either do it outside where nobody will mind the mess, or do it someplace where you won't get caught. I usually do a batch of 10 or so boards at a time and keep them in reserve. Be careful not to scratch the paint when you store them. (But if you do, you can touch it up later.)