Etching Color PCBs

I purchased 8 sheets each of red and blue single-sided copper-clad laminate, 4 inch × 6 inch, from abcfab on eBay. I paid $1 per board, plus shipping. (See the previous page for examples of the color PCBs.)

To etch the single-sided color printed circuit boards, I generally followed the steps described in my homemade PCB tutorial. I began by moving my existing Sandwich circuit layout such that almost all of the traces were on the same side. There was a little extra room on the 4x6 boards, so I created some additional circuits to make it easier to wire the DPDT line-following switch.

Next, I copied images of the circuits to Microsoft Visio. This allowed me to arrange the various layouts to fit 4x6. Also, from my machining experience, I knew such vector-based drawing programs are good for specifying the exact size of the image when printed. So, I can take high-resolution screenshots from the layout program and output them in fine detail at their final dimensions using Visio.

Multiple circuit boards laid out in Microsoft Visio Bones the Boston Terrier on a PCB mask

Left: Multiple circuit boards laid out in Microsoft Visio. Right: Bones, the Boston Terrier, on a PCB mask.

For the fun of it, I snuck in a picture of my dog. If you’re going to the trouble of etching your own PCBs, you should take advantage of the ability to include logos, different fonts, and images in your printouts. Contrast that to PCB fab houses that usually require Gerber files created on more-restrictive circuit design software.

Next, I printed the circuits onto Press N' Peel Blue transfer paper using a laser printer. Some people substitute glossy stock or magazine covers to reduce costs.

PCB pattern printed on Press N Peel transfer film Close up of PCB transfer with printer steganography

PCB pattern printed on Press N Peel transfer film. Right: Close up of PCB transfer with printer steganography.

Little Yellow Dots

What’s this? Why is there a pattern of dots sprayed in between traces?

The government is justifiably concerned that color printers will be used for counterfeiting currency. So, printer manufacturers have added a repeating encoded pattern of little yellow dots to trace the printout back to a person or place, by identifying:

This is called forensic watermarking or printer steganography. While this may be beneficial to us all in protecting the money supply, it can also be used to target political dissidents or whistleblowers. Keep that in mind the next time you drop off a laser-printed “completely anonymous” complaint in your boss’s mailbox.

UPDATE: The little yellow dots are a security vulnerability. A DARPA-funded contest in October-December 2011 provided a prize for whoever could reassemble some shredded documents. Otávio Good and his team used the little yellow dots as a pattern to solve the more difficult pages. That means bad guys can use the government’s own mandate to uncover government secrets, corporate proprietary information, or even to aid in identity theft from financial printouts shredded at home. Whoops!

For the purposes of this article, my concern is that the extraneous dots will affect the circuit. They do, in fact, make it to the copper layer.

Forensic watermarking on PCB

Forensic watermarking on a PCB.

Fortunately, the dots are disconnected and tend to fully etch away. Those few that remain are likely to fall off when the board is scrubbed. The downside is that little bits of loose copper may be floating around -- potentially causing short circuits on fine-pitch chips. So, scrub and wash your board thoroughly.

A better option is to avoid the dots in the first place. On my printer, switching it to black and white mode turns off the yellow dots. I have to explicitly tell it not to print color (usually in the Printer Settings on the Print or Page Setup dialog). An image without color portions is not sufficient to avoid the yellow dots.

Of course, your printer may work differently. Check the printout with a magnifying glass and/or a blue LED to search for the little yellow dots.

With your printout in hand, the next step is to transfer it to a clean copper clad board. You can do this with a clothes iron or laminating machine. The toner covers the copper areas that you want to retain on the board. The remaining exposed copper will be chemically removed in the next step.