Originally posted on my personal blog, Meat and Networking.
LVL1 is great. A place for creative and motivated people to get together and goad each-other into doing more creative things. It's also a great gathering place for tools, as well as knowledge. A few months ago, the spoiled electrical engineer that I am, I never would have considered making my own PCBs. Any project worth taking off the breadboard was worth sending to China to get made "right."
Of course, there isn't always time and money to send something to China. Today's installment is the Sumo-bot board I'm trying to put together for the Hive13 sumobot competition. Unfortunately, it doesn't look like poor Snoopy bot will make it to the ring, but the board making process itself is worth talking about.
Laying out a PCB using software like Eagle is beyond the scope of this post. If you can follow the appropriate Sparkfun Tutorial, it's pretty easy to pick up. Something to note: for single sided home-made PCBs, put all traces and surface mount components on the BOTTOM layer. Put any necessary jumpers on the top layer. When you're ready to print, just turn off all the layers you don't want turned into copper.
So, to make a PCB, you'll need a few things:
- Cheap Photo Paper
- A Laser Printer
- Copper Clad FR4
- A laminator with a straight feed path
- OR a clothes iron
- A sink
- Plastic, non-reactive bowls or tupperware tubs
- Muriatic Acid (Hydrochloric Acid, sold as a pool supply)
- Hydrogen Peroxide
- Nitrile or Latex Gloves
- Baking Soda
- Drill Press
- OR Dremel + Dremel Drill press
- Really tiny drill bits
You can pick all of this stuff up at a hardware or grocery store. Muriatic Acid is simply HCl, and you can get the stuff for about $8 a gallon in the pool supplies. A gallon lasts a LONG time. A laminator with a straight feed path can be had for about $30. You might have to carve out the back of the thing to allow the board to feed through. A clothes iron will also work, but you'll have to be a lot more careful. Copper Clad FR4 can be had at Radio Shack, although they aren't the cheapest source.
So, let's get started. Step 1:
Print your circuit board on the photopaper, shiny side up.
Cut out the design and line it up with your copper-clad board. Once you have an idea for how much PCB you'll need, score the board on both sides with a utility knife, and break off the proper amount. (The proper amount is just slightly larger than your PCBs).
Rough up your PCB under running water.
Use some scotchbrite or something here. You don't want to remove copper, you just want to make the surface a little rougher than it was before. Make sure you rinse off any oil that may have transferred from your skin during handling. After this step, be careful not to touch the surface of the PCB until after etching.
Dry the PCB thoroughly.
Line up the cut-out photo paper images of your board, and feed the PCB into the laminator.
When you feed the paper and PCB into the laminator, be very careful to ensure that the paper does not slip or slide. After the first run through the laminator, they will stick to the board, so you don't need to be careful.
Feed the PCB and paper through the laminator several times, from different angles. I usually feed through 10 or 15 times. Careful, the PCB will be very hot to the touch.
If you're using an iron here, the same rules apply. Don't use enough heat to singe the paper, but not much less than that. Apply smooth, even pressure, and go over the PCB several times. Be very careful and consistent during this step, or you'll get unreliable results.
Rinse the paper off the PCB.
First, run warm water over the paper until it is soaked through. Then, using the pads of your fingers only, rub the paper off the board. After a few minutes of this, you should be left with the toner only.
Be very careful, and make sure there isn't a thin layer of paper or glossy film still attached. This will not etch properly, and will cause bridges.
After this step, you should end up with a board that looks like this:
You'll notice that there is some residue left over from the paper in this image. After I took this picture, I soaked the board a little longer, and was a little more careful about removing the paper.
If your board doesn't look right here, use acetone and wash the toner off. Then, repeat these steps from the beginning. Eventually you'll end up with a board that can be etched.
Mix your chemicals.
Please, exercise EXTREME caution in this step. These chemicals can badly burn you. Wear latex gloves, wear safety goggles, and ALWAYS add the Muriatic Acid to the Hydrogen Peroxide, NOT the other way around.
Do this outside, or in a well ventilated room. Muriatic Acid is not pleasant in the lungs.
Using non-reactive measure cups, mix 2 parts hydrogen peroxide and 1 part muriatic acid. 1 cup hydrogen peroxide and 1/2 cup muriatic acid is plenty to etch a PCB.
In one tupperware tub, I have the acid mixture. In the other, water.
Toss the PCB in the acid bath, and watch the copper dissolve.
As the etch progresses, it helps to agitate the acid mixture. I simply rock the tub back and forth. The copper turns the bath lime green.
Here we're nearly done. Make sure the copper on the bottom of the board has dissolved, as well. When all the copper is gone (check between all the pads and traces), remove the board from the acid bath (using tongs!) and dip it in water. At this point, the board is safe to handle with hands.
When you're done with the etchant, pour it into a non-reactive container, and keep it until there's a local chemical disposal day. Supposedly, you can revive the etchant with some additional hydrogen peroxide, but I haven't successfully done so yet.
You can neutralize what remains in the tub with some baking soda.
Honestly, I just throw the baking soda away, and rinse out the container, but this definitely isn't the best way to handle things. Run the water for a long time, the etchant can corrode your pipes.
Remove the toner.
Rinse the board with acetone, and scrub until all the toner is gone.
You'll notice some bridges in this picture. At this point, you'll want to go through with a multimeter, and make sure any suspect portions of the board check out electrically. You can fix any bridges with a set of dental picks, or an xacto knife.
At this point, you can also square up the board by scoring it with a knife, or using a jigsaw.
Using a drill press and really tiny drill bits, drill out your PCB in the appropriate spots.
I'm using a Dremel drill press and some drill bits from Electronics Goldmine.
In order to avoid breakage, and reduce hole ovularity, adjust the drill press to that it begins just above the surface of the PCB, and stops just beyond the other side of the PCB (adjust press for minimal travel).
Begin your sumobot exhibition matches as soon as possible.