Making Excellent Printed Circuit Boards
This article was originally written as a letter to some of my friends who wanted to know why my printed circuit boards turned out so well. After I sent it, they suggested I turn it into an article. So, here it is:
There are only a few secrets to making really good printed circuit boards. The first is to get everything completely clean. The second is to use a good etch resist. Here are the materials you’ll need:
- some black Sharpie® brand permanent markers (from a stationery store)
- the board to be etched
- lacquer thinner, model airplane dope thinner, or acetone
- automobile rubbing compound (without wax, available at auto supply stores)
- a 1/32″ drill bit and a 1/8″ drill bit
- a plastic tray (Tupperware®, Rubbermaid®, etc.)
- a piece of 1/8″ x 1/4″ balsa wood
- ferric chloride (available at Radio Shack®) or ammonium persulphate etchant
First, buy yourself three Sharpie brand permanent markers. Get the ones with black ink as they seem to work best. Get two fine point (which really has a bullet-shaped medium point in my opinion), and one ultra-fine. The ultra-fine has a steel barrel-tip with a very fine marker poking out the end.
Label your jar of lacquer thinner “Board Cleaner and Etch-Resist Remover”.
Next, clean the board very well. I found that automotive rubbing compound works really well for that. It gets really black and messy while you’re doing it, but rinse it off, and voila, shiny copper. After you’ve rinsed it, use some lacquer thinner to get any traces of oil or grease off the board. From this point on, only handle the board by its edges. If you must touch the surface, put something between it and your fingers so you don’t get any skin oils on it. It may be tempting to use sandpaper to clean the board, but don’t do this. You will make millions of tiny grooves in the board, which may not fill with etch-resist, and you’ll get hairline cracks in the finished traces.
The next step is to drill the holes. Use a 1/32″ bit. Use a piece of perf-board with holes on 1/10″ centres as a guide, and make sure you drill from the copper side, not from the component side. If any of the holes need to be larger, enlarge them now (eg. with a thicker bit, or a needle file).
Now take a 1/8″ drill bit, and by hand, use it to remove the raised ridge of copper that for some reason forms around each hole as it’s drilled. Don’t over do it. You don’t want to make the hole in the copper larger than the hole in the board or it will be no fun to solder, since the component leads won’t be close enough to the copper.
Take a loop of masking tape and tape the board, copper side up, to a piece of cardboard (eg. the back of a writing pad). Press it down flat (but don’t touch it with your bare fingers). Now you have a handy means of handling the board and holding it still while you draw the traces on it.
Next, draw all the pads. For this I use the larger of the two markers. I generally start by putting the tip of the marker in the hole and turning. This draws a nice circular pad around the hole. After you gain some skill in this, you can run the tip of the marker around the rim of the hole and make a larger pad that way. The rim of the hole will bite into the marker and keep it from sliding all over the board. Keep this particular marker for making the pads, since making the pads tends to wear out the marker tip a bit and it’s no longer so good for drawing traces.
After all the pads are done, using the second large marker, draw all the traces that don’t have to go through tight spaces (like between pins). The traces that you draw should be about 1/16″ wide. Any power or ground traces that are next to the edge of the board should be extended right to the edge of the board (especially if they will be handling motor currents).
Now, draw the remaining traces that do go through tight spots. Use the super-fine point marker for this. The super-fine doesn’t seem to put the ink on as thick, so go over each trace a few times.
Inspect the board carefully. If there are any areas where the ink looks thin, go over them. Dabbing the ink on with the marker tip works well.
Let the board dry for at least 2 hours. The ink is dry to the touch almost immediately, but like paint, it’s still pretty soft for a while.
Get a plastic tray whose bottom has about 4 to 8 times the surface area of the board, and put about 1/4″ of etchant in the bottom. Microwave on high for 20 to 30 seconds (don’t let it boil, or someone will be very angry with you). Do not put the board in the microwave!! If you don’t have a microwave, put the whole bottle of etchant in a sink full of hot water for half an hour first. Open it occassionally to relieve the pressure.
Place the tray on a table (on some newspaper), with a 1/8″ x 1/4″ strip of balsa under the middle of it to act as a pivot for rocking it. Place the board in the tray, copper side up. Rock the tray constantly while the board etches. It will take about 20 minutes.
When done, rinse the board under running water for at least 2 minutes to get all the etchant off. Then, using tweezers, dip the board in the lacquer thinner and swish it around. Take it out, wipe it off. Do this a few more times to get all the etch resist off. The copper will have microscopic fissures in it and you want to get all the ink out of these or soldering will be a pain.
Try not to touch the surface of the copper after etching either or you’ll get oils on it and it will be hard to solder. If you’re not going to use the board right away, wrap it up tightly in plastic wrap to keep it from oxidizing.
Clean all component leads. I find the best way to do this is to scrape them with an X-acto knife. They should be as shiny as the board.
Use at least a 30W iron. You are much more likely to damage a component with a 15W iron because you need to hold the heat on it longer. Personally, I use a 45W iron. You should also clip an aligator clip onto the lead you are soldering when soldering a semiconductor (transistor, MOSFET, diode, IC). This will prevent excessive heat from reaching the component.
Feedback from a Reader
A reader of this page writes…
A quick note about the Sharpie. I thought I would try the Sanford “Industrial Super Permanent Ink” Sharpie. It says on the pen, “remains permanent under most chemical washes and extreme heat and steam”. They were right beside the regular Sharpie in the store. So I thought “I’ll try the Super Sharpie” figuring it would be more resistent to the ammonium persulfate. The results were very poor compared to the regular Sharpie. I don’t know why. When I tried the regular Sharpie under the same conditions the results were excellent.
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