On the previous page, I showed how to pump etchant onto copper clad boards, as part of creating color PCBs at home. After etching, the final steps are drilling and cleaning off the toner.
The advantage of drilling holes after etching is that the etched copper tends to guide the drill. I say “tends”, as I still ended up with a couple of errant holes by being a little too sloppy.
Drilling error missed PCB hole.
Notice the bare spot in the middle of the copper where the hole should have gone. If you’re close enough, the divot ends up acting like a centering mark, as though you had used a center punch.
Okay, I blew a couple of holes. Most of my holes were drilled accurately, and none of the misaligned holes had a significant impact.
The black toner needs to be removed from the holes and pads were components will be soldered. Technically, you don’t need to remove the toner from the connecting traces or anywhere else that won’t be soldered.
In the past, I’ve used a scrubbing pad and lots of manual labor to remove the toner. However, many people are recommending acetone (nail polish remover). The toner comes off the copper almost instantly.
Unfortunately, when removed with acetone, some of the toner (or Press N Peel residue) appears to react or embed into the substrate. You couldn’t care less about darkening an ordinary yellowish-green PCB, but color and crispness matters with these beautiful blue and red printed circuit boards. I spent hours scrubbing at the bare areas to remove the toner grunge. Eventually it looked okay, but it no longer has the same brilliant shine as the side without copper.
Therefore, I don’t recommend using acetone to remove toner on boards where color is important. On a positive note, ferric chloride does not appear to stain or discolor the PCB during etching.
My boards suffer from the same minor problems as everyone else’s homemade boards. The most common issue is missing or uneven transfer of toner when ironing the design to the board. This is particularly problematic in the corners or edges.
Poor transfer in corners.
The copper traces around a pair of holes are completely missing in the photograph above. Also, large sections of text are missing from the bottom of the board. (It should say “R4 Photo”.) This is caused by my failure to spend enough time with the iron in the corner of the board.
Below, notice how the same letters (r, o, m) turned out a little bit differently from each other. This example comes from the middle of the board. Therefore, it is unlikely this came from user failure to iron evenly. Yet, it is still related to the temperature, pressure, and time that the iron spent in that area. This suggests a lower limit by which details can be rendered repeatedly using an amateur process.
RobotRoom letters all etch slightly differently.
For comparison, here is the same text, at the same size, from the same place on the same circuit on a professionally manufactured PCB.
RobotRoom professionally etched.
One last issue that I ran into was narrow areas of copper detaching from the substrate. For example, the area around some screw holes came off during drilling.
Failure of copper to adhere. Left: Good. Right: Fell off a different hole.
I don’t know if this is a weakness in the color boards themselves, or in the order in which I make my boards. Clearly the copper would not have pulled off if the holes had been drilled before etching.
Notice how much brighter the blue color is where the copper fell off? The darker areas are due to the acetone and toner issues that I described earlier.
Despite my focus on the few problem areas, the boards turned out well and the circuit works perfectly. It is certainly better than point-to-point wiring.
(Update: Use low heat and greater pressure for better results. Use lacquer thinner to remove toner, rather than acetone, to avoid altering the color of the board.)
This photo illustrates the various stages of home etching PCBs.
Stages of etching a homemade PCB.
Left to right:
The image of my dog is generally recognizable. Fine details would be lost if I removed the toner from the picture of the dog. Therefore, I encourage you to avoid cleaning logos or other images.
To accentuate the red and blue PCBs, I selected a clear DIP socket. Let’s see how it looks...