Circuit Etching

Circuit Etching

This is my process for etching circuit boards using the photoresist method. The video is a quick overview of what I do. Scroll down for details.

What You'll Need

Toner Transfer vs. Photoresist

The process I use involves exposing a presensitized board to a UV light. I first tried with toner transfer, the other well-known method for circuit etching, since it was slightly cheaper. It turned out to be more of a hassle than it was worth. The much better quality of the photoresist boards I made was definitely worth the few extra dollars. Another advantage of photoresist is that your template can be used indefinitely and you don't need to print for every board you want to make.

Preparing the Board

Start by printing our your design on to the transparency film. I use Eagle to design my boards. Make sure that the output is solid black and mirrored. It needs to be mirrored so that the side with the toner will be closer to the photosensitive board during exposure.

Printed design

Cut out your design and tape it to the inside of the picture frame. Wipe off everything with a microfiber cloth first.

Taped to frame

Preparing the Developer

Put on latex gloves since the developer is toxic. Mix one part developer with ten parts water. The "Always Add Acid" rule applies, except instead of acid, add the positive developer last. This is because the liquid that's already in the container can splash when you add in something else. In this case, a little splash of water is much less harmful than developer.

Pouring water

Exposing the Board

This next part needs to be done in a dim room. I turned a room in my house into a near-darkroom by covering the window with aluminum foil. You need to minimize premature exposure of the board to UV light. A red lamp is useful since it provides illumination without producing too much UV light.

Take the presensitized board out of the packaging. If you want to cut the board with a hacksaw or tin snips, be aware that some of the photosensitive layer will shrink away from the cut so make sure to leave a margin of about a centimeter or two. Peel off the protective layer and place the board face down on top of your design.

Placing board

Tape the board down and secure the back of the picture frame. Flip the frame over and expose it to UV light. Since I don't have a UV bulb, I just shine a plain white lamp directly on the board. Eight minutes should be more than enough time.

Exposing board

Developing the Board

Take the board out of the picture frame and place it face up in the developer solution you prepared earlier. Swish around the container. If you have a foam brush, you can use that to help speed up the process.

Developing board

In four or five minutes, you'll be able to see your design clearly. Take the board out of the solution and rinse it off.

Developed board

In my experience, the developer solution isn't reusable. Dispose of it by pouring it down the drain while running the sink.

Etching the Board

This part of my process could use a little more work. I use Cupric Chloride which is supposed to be reusable, but takes a really long time. In practice, I've always had to remake the Cupric Chloride. I plan on switching to Ferric Chloride.

Prepare the etchant by mixing one cup of Hydrogen Peroxide with one cup of Hydrochloric Acid. Following the AAA rule, add the acid last. Make sure to wear the PVC-coated gloves while handling the acid. Don't use any metal utensils or containers because they will corrode.

Pouring acid

Place the board in the solution and let it etch away the excess copper. Agitate it with a plastic utensil every few minutes. I had to wait about an hour.

In etchant

Take the board out and rinse it off.

If you need to dispose of the Cupric Chloride, make sure to neutralize it with baking soda (NB: it is very dangerous to add ammonia) first. Don't pour it down a metal sink.

Finishing the Board

There's still photoresist on the remaining copper. Wipe it off with some acetone and rinse it one last time.

Wiping board

That's it. The etching process is done!

Finished board

Now you can cut the board to its proper dimensions and drill any holes. I use tin snips and sandpaper to reduce the size and smooth the edges. For my through-hole boards, I use this miniature drill kit from Jameco.

Credits

This guide is based off of tutorials by MAKE and HackADay.

Music by www.pacdv.com/sounds/.

If I made any mistakes or omissions, please let me know. I would also appreciate any feedback.

Circuit Etching