Making Printed Circuit
Boards:
Most of the projects on these web pages include a
"GIF" format image with the circuit board copper trace layout.
There are several ways to translate these images into a printed circuit
board. Steps and options are detailed below—in short, print the
image to some kind of hardcopy, transfer that to the circuit board copper,
etch, and solder in the parts.
Print the Circuit Image:
If you have an Apple computer, you may be able to scale the image correctly with your printer driver, and thus print the correct size directly from your web browser. If you have a PC, first save the image from the web page to a file on your computer. With Netscape, this involves clicking the right mouse button with the mouse cursor on the image of interest, pull down to "save image as . . .", and selecting a location and name for the file. Next, open the image in a graphics program of your choice. A program available on the web for trial use is "Paint Shop Pro", downloadable online at http://www.jasc.com/ . Try printing a copy of the image. Use the one centimeter scale on the image to see how far off in scale the printed image is. Adjust the printed size of the image by using the graphics program print set-up utility. With Paint Shop Pro (PSP), this involves pulling down "file" to "page setup", then adjusting the size of one dimension of the printed image with "maintain aspect ratio" checked. You can do this by trial and error, or use a ratio of measured to expected to dial it in. Say the measured 1 cm mark is printing as 1.3cm and the PSP print set-up shows an image width of 5 inches. So (5 inches)(1cm/1.3cm)=3.8 inches. Plug in 3.8 inches as width on the PSP print set-up window, and the measured 1 cm mark should be very close next time you print.
Prepare the Printed Circuit Board (PCB):
RadioShack carries a PCB kit with etchant, a board, a tank, etch resist pen, and resist remover that would make an easy way to start (part 276-1576 for $13.99, or only 4.5x6" double sided PCB part 276-1499 $3.79, or only etchant part 276-1535 $3.49). Digikey (1-800-344-4539) sells these components as well (1/16" 3X4.5" single sided PCB part PC5-ND $2.78, 1/16" double sided PCB part PC-55-ND $2.10) For these small boards, actually 1/32” is plenty thick and much easier to cut.
Cut the PCB roughly to size. This can be a trying task with a hacksaw, but a power jig saw or scroll saw with a blade intended for metal makes quick work of it. Final shape with rough sand paper—ideally on a belt or disk sander.
If you are making a double-sided PCB copper trace pattern, use a piece of packing tape to cover the copper on one side while you work on and etch the other side. Cover the new trace pattern with tape while you do the other side. If you start out with double sided PCB and your final board will only have copper trace on one side, protect one side of the copper with tape while you etch off the other, then remove the tape and work on the remaining copper side.
Most problems with a poor final result I’ve had were related to preparation of the board. The copper has got to be squeaky clean, smooth, and free of corrosion. Oils on the PCB keep the resist stuff from sticking. Scratches or pits in the copper leave gaps or thin spots in the resist. Corrosion makes the etching take longer as it actually protects the underlying copper and makes the etch resist have to last longer. I’ve used 600 grit wet-to-dry sandpaper to shine it up under running water, but others recommend using a wax-free automotive rubbing compound. I’ve used soap and water, then alcohol to clean the board, but others have used automotive wax and silicone remover, or dope thinner to do the same. I usually just clean the piece of PCB right before I need it to keep corrosion from reforming, wash my hands thoroughly before handling, and handle only by the edges.
Etch Resist Ink Pen Method.
Print a copy of the circuit trace pattern to scale. Use a tack or similar to punch holes in the paper at each of the solder pads (where you will eventually be drilling holes). Hold the paper over the PCB, and use a felt-tip pen at each of the holes to mark the solder pad locations on the PCB.
Use a awl or small punch to press a tiny dent in the copper at each of the solder pad locations to help hold the drill in place, then drill each of the holes. I use a Dermal tool with a 1/32 drill, holding the PCB over an old magazine, You can use a 3/32 or 1/8" drill bit by hand to gently remove the raised copper at the margin of the drilled hole (too much and soldering will be tougher).
Use double sided tape or a loop of tape to tape the PCB to a suitable work surface.
For an etch-resist pen, get a couple black Sanford "Sharpie" felt tip pens from your local office supply store. The "fine point" is good all around with its actually fairly large bullet tip, but the "ultra-fine point" can be used for really fine detail work. Use a "fine point" marker pressed into the drill holes to make the round solder pads around the drill holes. Use a different "fine point" marker to make the circuit traces, as the first marker gets quickly mashed. You can use masking tape applied to the under side of a ruler to keep the ruler up off of the PCB to make cleaner lines, and you can use acetone (finger nail polish remover), alcohol, or dope thinner to remove the resist pen. Even though the marker ink appears to dry within seconds, give it several hours to really cure before you dunk the PCB in the etchant. Triple check everything, because you DID miss a trace, and you DID put one in the wrong place. Done that. If your quest is for aesthetic finery, you may be disappointed with this method initially as uniformity on the PCB traces is very difficult, and each PCB is a unrepeatable masterpiece. This method works best for single copies of simple circuits that have plenty of space.
Dry-Transfer Method:
RadioShack sells a packet of dry-transfer etch resist patterns (part 276-1490). I notice Digikey (1-800-344-4539) also sells an assortment pack ("Direct Etch Transfer", Assort pack, 8 sheets, part ER-2-ND $7.80) though I have not seen it.
Use the same method as above to print a copy of the circuit pattern, punch holes in it, and use a pen through the holes to put the location of the solder pads on the PCB. Drill the holes AFTER the board is finally etched. Use double sided tape or a loop of tape to tape the PCB to a suitable work surface.
If you cut out individual resist pads and traces, you will find them exceedingly difficult to position accurately, as the resist sort of sticks where it falls and it tears easily. Instead, cut the translucent transfer film with black resist and white opaque paper backing into strips, the longer the easier they are to handle. Do not touch either the PCB copper or the black resist with your fingers lest the resist float away when you eventually dunk the PCB in etchant. Note that the opaque white backing paper easily falls off the translucent transfer film and black resist—not a problem since you only need the backing to protect the resist from your fingers. With a strip of 15 round resist pads in one hand while protecting the resist from your fingers with a piece of backing, transfer individual resist pads to the PCB by rubbing the transfer paper with the back end of an xacto knife handle or similar (or an actual official burnishing tool). Then apply the connecting resist traces. Lay the strip of black trace with transfer film on the PCB to measure the length you will need, again protecting the black resist material from your fingers with a piece of white opaque paper backing. Use sharp scissors to cut through the black resist trace completely but don’t cut completely through the translucent transfer film—your length of resist trace will be hanging with its transfer film by a corner of transfer film. Position the trace, burnish it in place lightly to fix the position first, then generously to fix it to the PCB and release it from the transfer paper. Cut off the excess transfer film, and repeat with the next segment of trace. If you use a knife point to scratch away the center of the solder pads so that a central hole will be etched in the pads, drilling later will be easier. Finally, burnish the entire board again under a larger piece of the backing. Triple check everything! After that heinous eyeball-popping exercise, you know you must have missed something, requiring you to start all over. "NEVER AGAIN!" I said after the first PCB. It does get considerably easier with a little practice, and I can do one or two PCB’s in an evening without too much trouble. You can make reasonably complex and compact circuits this way, but you can hardly do a production run.
Toner Transfer System Method:
This involves using
special paper and a laser printer or copier to generate a transfer pattern,
then iron the pattern on to the PCB, and etch it. In essence, the laser
or copier toner becomes the resist. After you re-fuse the toner, this
time to your PCB using an iron, the board and paper is submerged in water, and
the paper is released, leaving the toner on your PCB. The process works
well enough that the toner is difficult to remove from the PCB, requiring a
vigorous scrub with acetone. Since you transfer a computer image directly
to the board, you can add graphics, your name, or other labels to your
handiwork with ease. You can order the transfer paper from an electronic parts
supply company such as Digikey
(1-800-344-4539, "Toner Transfer System", part TTS-5-ND or TTS-10-ND
for 5 or 10 8x11" sheets at $14.95 or $27.95). The paper comes with
detailed instructions, but a few notes might be helpful. First, you can
print many, many patterns with no more difficulty than an individual pattern,
simply by cut-and-pasting the circuit pattern to a larger graphic image and
printing a bunch of circuits then at the same time. You can also cut the
transfer paper to small pieces and tape a piece to a regular sheet of
paper, then run the larger sheet with tiny piece of transfer paper through your
copier or laser printer, thus using very little of the rather expensive
transfer paper. Needless to say, make sure you have the pattern just so
on cheap test laser or copier paper before you commit a piece of the toner
transfer paper. Remember that the pattern on the transfer paper needs to
be a mirror image of the final PCB since the transfer paper sticks face
down on the PCB. If you keep your patterns small, you can easily and
handily use your Monocoat iron to iron the transfer paper to the board. I
use a Monocoat temperature gauge and a cooking timer as suggested in the
instructions to make the pattern stick well but not melt. Generous
even pressure is needed with the iron for several minutes. Too much
pressure and the pattern may smear, too little and a poor transfer
results. With a little practice, I can run off a dozen boards in an
evening.
Photographic Transfer Method:
I believe most
commercial products are produced using this method. The process involves
generating a photo mask by transferring the trace pattern to a
transparency, which can be done with a laser printer or copier. The mask
is placed over a PCB previously treated with a photosensitive resist
material. The PCB with mask is exposed to light, then the PCB is fixed
and washed, then etched. The resist exposed to light (not covered by
circuit trace on the mask) washes off, leaving the resist trace pattern on the
board. Once such a system is set up (mask making, PCB pretreating or
purchasing pretreated PCB, light box and holder, developer, etc.) the system
works great, and can be used for very complex, detailed, and large
boards. Once you have used this method, you will NEVER use any of the
above methods again—it is unbelievably easy, extremely reliable, and you can
make a boatload of these tiny circuit boards in one session. The only downside is a little extra
expense initially with the light ($35) and the developer ($5), and the presensitized
boards are a little more expensive.
The photo here shows the artwork on a transparency over the PCB (the
resist is greenish) under the flourescent light. M.G.
Chemicals makes the boards, etch kits, and exposure kits and has an online
tutorial. You can easily print
your own artwork on a transparency—I used my inkjet printer with some regular
inkjet overhead projector “transparency film” purchased at a local office
supply store. The printed circuit
boards at the top of the this page was created using this photo method.
Etch the PCB:
Some people heat the etchant initially to speed the process. You can warm the bottle by placing it in a bowl or sink of hot water. Probably heating the etchant takes more time (and exposes you to more risk—some heat it in a microwave oven) than you will gain etching the PCB. Put your PCB in a plastic tray, and pour in the etchant, just enough to cover the PCB. Gently rock the tray to speed the copper removal. Make sure the trace side is up, as the etch resist will easily rub or flake off against the bottom of the tray (also the reason only one side of a double sided board can ordinarily be done at a time). Etch time is about 30 minutes. Once the background copper is removed, rinse off the etchant, and remove the etch resist.
Drill the PCB:
A drill press is ideal of course, but expensive. A high speed motor such as a Dremel tool works well with a little care. Drilling the holes with a hand drill is possible, but you will break many drill bits. A 1/32" drill is a good all-around drill bit size, though somewhat large for most components. You could use a #71 bit (0.026 inch) for components and the 1/32 inch (about 0.031 inch) for larger resistors and connecting wires. I use a Dremel tool with the PCB on an old magazine, or hold the Dremel horizontally on a table and lean the PCB onto the drill bit.
Solder the PCB:
See the soldering article on this web site to finish up your
creation.
Written by Rob Crockett
August 30, 1998