There are some good Instructables on using toner transfer, but after doing my own for a while I have some refinements on the process that I want to share. You should be able to create high-quality, well aligned double sided boards every time.
If you are just dealing with a basic board for 0.1" pitch through hole components this is probably overkill. A good instructable for those kinds of boards this one by pinomelean.
I have made excellent boards with 8 mill pads and 12 mill clearances.
There are a few secrets. 1. a laser printer. 2. a hot laminator. 3. (The big secret) Parchment cooking paper. 4. Careful and diligent cleaning of the board.
If you follow my directions to the letter you can get great results.
Step 1: Gather supplies and materials
Laminator. Digikey part number 182-1031-ND. $114 at time of writing.
- MCUman says "Harbor Freight sells a 9" laminator for 30 bucks. I've had mine for a couple of years now, I use it often, and it works GREAT! Item number 92499."
Laser printer. Mine is an HP LaserJet P1102w.
- dasclown says a Dell 5100 cn laserjet did not work.
- If you know of one that does/does not work, comment please.
- Scotch Bright sponge
- etching "tank"
- Leather gloves for handling the hot board (or a towel, or your shirt. It's not that hot.)
- Sewing needles
- Alligator clip wires
- Drill press or dremel and tiny drill bits needed for your design. Harbor Freight sells a cheap multi pack of tiny bits.
- Glass cook top cleaner
- Tarn-X tarnish remover
- Parchment paper from the grocery store
- heavy duty zip top bags
- Kapton tape (1/4" is best) - no substitutions!
- 1/2oz x 1/16th" copper board
- Stranded copper wire. Something with fairly thin strands. Jumper wires the cat chewed in half work good. (See photo 3)
- Rubber gloves
- Muratic Acid (or Acid Magic from Ace Hardware)
- Hydrogen peroxide
- glass measuring vessel
- plastic/wood utensils
- ecthing "tank" - Pyrex dish
- rinsing tank
Step 2: Pre-heat the laminator
- Turn your laminator on now.
- Push the 5mil button.
- Let it run at least 25 minutes.
- If it goes into auto-shutoff turn it back on
Step 3: Print pattern
- Print your top layer pattern out on a regular sheet of paper reversed.
- Tape down enough parchment paper to cover the pattern with a one inch or better margin.
- Run the paper back through the printer.
- Print your bottom layer (not reversed) on another piece of parchment. You can re-use the first piece of plain paper and tape for the second parchment if you are gentle.
- pick out the right size of copper board and cut it to size. leave at least 1/4" margin from the circuits on one or more edges to have a solid place to tape.
- Trim the parchment paper fairly close to the traces, but leave a 1" or better margin along on edge to allow taping them together. When you cover the board, it should stick out on 3 sides and the paper should hang over the board on the fourth.
Confused? Sturmy explains it really well.
Ah, now I understand. So you print onto the paper to see where and how big the image will be. Then you tape parchment onto the paper so that the paper will be the right size, but the toner will be printed onto the parchment.
Then you print again, except this time the toner is on the parchment which you can detach from the paper and transfer the toner to the copper board.
offtherails2010 has some other hints (paraphrased).
1. You can use double stick tape under the parchment paper rather than Kapton [I tried this and it works great. You can even re-use the tape and paper easily. -Dustin]
2. If the toner doesn't stick well to your parchment or "Siliconized Baking Paper" you can spritz both sides with 99.9% Isopropanol to promote adhesion. Works on the copper as well.
Step 4: Clean the board
- Put a generous dollop of the stove cleaner on your board.
- Using the green side of the sponge, give it a good scrubbing.
- Flip the board and scrub the back too.
- Rinse the board well.
- Check how the water sheets off the board. If it's not sticking evenly to the board, scrub some more. (see pictures)
Step 5: Use the tarnish remover on the board
- Put the board in a clean plastic zip top bag
- Put about 1 tsp Tarn-X in the bag.
- Push out the air, seal the bag and agitate gently for 15-20 seconds.
- Take the board out by the edges and rinse it. (Note: water will not sheet the same way as before, don't worry.)
- Pat the board dry with a clean cloth or paper towel.
The board is now ready. Consider putting it in a plastic bag if you won't be using it right away (make sure it's really dry). Remember not to get fingerprints on it.
Step 6: Align the side and tape to the board
The Kapton tape is important. It doesn't warp, melt or stretch in the laminator. I tried all manner of other tape and was disappointed.
- Gently line up the two halves with the toner facing inward. If you rub the toner together too hard it will rub off.
- Trim the "overhang" side of the two halves so it's strait and matched on both sides.
- Cut off some tape strips that are about as long as each side of the paper. One for each of four sides.
- Fold or tape the halves so they line up exactly. It can be tricky with only two hands! Parchment is translucent so it's easy to do with any light. A tracing table makes it super easy.
- Tape the overhang together. Triple check your alignment now.
- Gently insert the board. It's easy to scrape off the traces with the edge of the board, so watch out.
- Starting from one corner, smooth out the paper and tape it down with the Kapton tap.
- Make sure the parchment is smooth and more or less tight. It doesn't stick well to the Kapton without some pressure. If it's not tight enough the last traces into the laminator will be off.
- Tape the other side down as well.
Step 7: Run the board through the laminator
- Run the board through the laminator near one edge.
- Run the board through different parts of the laminator 3 more times.
- Let it cool.
Step 8: Examine and touch up the board
- Remove the tape and the paper
- Examine the traces and make sure they all look good.
- Using a sharpy or paint pen fill in any large pads. The laser printer seems to have problems evenly filling in big areas.
- Check the longer traces carefully for breaks and fill them in with a sharpy.
- Use a sewing needle to remove any stray toner if needed.
Step 9: Etch the board
- Put 2 parts Hydrogen peroxide in the etch tank.
- Carefully add one part acid.
- Stir carefully.
- Put the board in and agitate. Flip and turn the board every 30 seconds. Try for an even etch.
- Once all the copper is gone on both sides, put it in the rinse water.
Quinn Dunki on her blog Blondihacks uses vinegar, hydrogen peroxide and salt. I never tried that but it sounds pretty nice, if somewhat slow. She also has a good writeup on using photo-resist methods to make really nice boards.
Step 10: Clean off the toner
- Use the bag trick again and soak the board in 2 tsp or so of Acetone for a couple of minutes.
- Rub the board through the bag with your fingers to get the toner off.
- Take it out and clean it with a rag or paper and some more acetone if desired.
- Let it dry
- Optionally use another bag and some liquid tin. I don't think it's needed if you are going to solder the board right away.
Step 11: Test the traces
- Clip the alligator leads to your meters probes.
- Put a sewing needle in the end of each lead.
- Turn your meter to continuity (beeps when you touch the leads).
- Test each trace to see if it's complete.
- Test neighboring traces to make sure they aren't connected.
- Use another needle to scrape away any copper bridges.
- Use a silver pen, conductive paint or solder little wires to patch any splits. (Rare if you use fresh etch).
Step 12: Process the through holes
- Using a drill press or dremel to drill out the through holes.
- Using the stranded wire, solder a jumper through all the holes.
- Check the through holes with the meter.
Update: I use liquid tin on the boards, but this Instructable shows another, cheaper DIY alternative. I'm not sure how suitable is it for fine traces like this board.
Step 13: Solder on the components and enjoy
- Use some Kapton tape and a sharp knife to mask of any areas of concern. For example where traces shoot the middle of under small components.
- Go to town with the soldering iron, or use a reflow method.
- Test connections with the meter.
- Power up and hope the magic smoke doesn't come out!
This instructable shows a great way to add a solder mask.