how to make printed circuit boards
(or at least how I make them)
How the toner transfer process works
The ink toner in laser printers and photocopiers is a plastic based powder that once heated melts then solidifies and bonds to the paper you are printing on. If you use a photo paper normally used for inkjet printing, the plastic toner will bond with the coating on the paper and form a layer of plastic on top of the papers surface. If you heat up the toner with a clothes iron the toner is liquified and can be transfered to copper clad board. There are many variations on this process. At the bottom of this page I describe the materials I use.
Decide on the circuits you want to etch. Print three of each PCB trace pattern on your photo paper. This way you will have a back up incase something goes wrong. Also if you want to build another board later on you will already have it printed out. On an 8.5x11 sheet of paper I print 3 of each pattern in a row across the page (depending on the size of the pattern of course). Then three of another patern and on down the page. Keep the printed patterns in a folder to guard against dust and contamination. as well as being able to find them later.
You must use a photo copier or a laser printer. An inkjet printer will not work because the ink in an inkjet printer is liquid and has no plastic to bond to the copper. The ink jet ink soaks into the paper and does not sit on top of the paper as with laser or photocopier toner.
If you only have an ink jet printer just print out your patterns onto a sheet of inkjet or plain paper paper, then take this to a copy place and make a photocopy of it on coated glossy inkjet paper (see the material list at the bottom of the page) The thicker the ink deposit the better. Print as dark as you can without getting foggy areas. Be careful with your printed photo paper and do not get finger prints or dust on it. A dedicated folder works well here as well.
Update: The quality of your toner print makes a big difference. The thicker the print the better the etch will resist the traces and stick to the copper board. Photo copiers seem to work best in my experience.
Hold the print up to a bright light . If you see through it it's not thick enough. Darken the settings until it starts to fog the print then back off one click.
Cut out your paterns and leave about an 1/8th inch border all around.
Now heat up your clothes iron while you prepare the board(s).
Update: The cotton setting on old irons is usually fine. For modern irons linen may work best. The paper backing usually gets yellowed from heat on my boards. On my 60's iron "linen" is too hot.
Cut the copper clad board to whatever size you need and file the edges smooth. I File at a 45 degree angle on both sides of the board to slightly round off the edge when the copper was cut, otherwise the iron may not make full contact with the edge of the board. Using the file makes the board more "finished" as well. I use a table saw to cut my boards but this is an expensive tool. I use it for other things so it's justified. Scoring with a razor knife works but it's too clumsy and inaccurate for me. A hack saw will work as well.
Take some #0000 steel wool and polish the copper side of the board well. The copper should be very shiny everywhere, corners and all. Make sure the corners are good and shiny. Did I mention the corners?
Use a paper towel or a known clean rag and wipe the board clean with Acetone, Denatured Alcohol or some kind of solvent. This removes the oil left behind from the steel wool and your finger prints as well as the copper dust.. Don't touch the copper side of the board from now on. Handle it at the edges only.
Place your transfer on the board and hold down an edge with your free hand while you place the hot iron on the transfer enough to tack it down. The heat will bond the toner enough so it won't move. Now place the whole iron over the transfer and press down for 5 seconds or so. This heats up the board and bonds most of the toner. Cover the whole board with the iron. When the whole board has been heated move on.
Take the iron tip and press down on the corners of the paper. Use the tip at a slight angle, enough angle so you get about 2 inches of surface area to concentrate pressure to small areas of the board. I usually will alternate between heating up the whole board and using the tip to press the corners middle and edges down. Use as much pressure as you can while not sliding things around too much. I use a small piece of pine board to raise up the board off my work table. Small overlapping circles work well to cover every bit of the board. The paper gets yellowed with heat. This is how I know I've heated and worked over the board enough.
Use the board space wisely. If you can plan out your builds you will save material by making a few transfers at once and on the same board.
Once you get tired or bored ironing the transfer on (usually about 3 minutes or less) let it cool down enough to handle and then place it in a tray with hot water from the tap and a couple drops of dish soap. I usually put a drop on each board and rub it in a little. The soap is a wetting agent and will help the water penetrate the paper. Let the boards soak for 30 minuets or so. Some times I get impatient and peel the paper off after only a few minutes. The paper you use may tolerate doing this.... Some papers come right off without much soaking at all.
Rub the soaked board with the edge of a finger nail to let more water penetrate. The more the paper is soaked the more the toner and the surface of the paper will separate cleanly. The softer the paper the better really. The backing resists water so getting though the initial layer will help saturate the paper which will come off quicker.
The old staples paper got pulpy right away which was nice because you could rub it off and not have to peel it as much. I believe the toner that bonds to the papers coating is a big part of the etch resist process. So you have the toner and the paper coating which resists the etchant.
Once the bulk of the paper is removed you are left with a some residual paper coating and pulp which will come off with more soaking and rubbing with your thumb. I use a soft tooth brush to loosen the little bits in the tight spots. You don't have to rub hard to get the bit's to rub off. More soaking with hot water will usually help. If you can wait, soaking overnight really helps loosen all the paper.
Make sure you have all the paper and coating off the copper. It's ok to have some on the traces but watch out for the copper between traces and pads. Anywhere the copper is covered with become solid copper once you etch. Use a loupe, reading glasses or magnifying glass to make sure your copper traces are clear of coating and blockages.
A tooth pick or exacto blade knife if a good tool to dislodge and clear the traces and pads. A lot of times the pad holes are blocked as well. It's easier to drill a clear pad hole since it becomes a pilot hole.
Once the board looks good you can fix any flakes of toner that come off inevitably. The trace is still visible usually and you can easily draw the missing toner in on the board. A sharpie will work but I have found that Staedler "Lumocolor" pens work better.
Usually a couple coats with the pen works well. Try not to press too hard with the pen as this removes ink when the second coat softens up the first coat. I try to dab the pen a little to get the most ink on the board.
Let the ink dry a few minutes or give it a quick blast with a heat gun or a hair drier. If the ink is wet the etchant will eat right through it.
By the way, any water resistant ink, paint etc will be fine as an etch resistant. Pens are easy because they can be drawn on , but if you are savy with a paint brush then go for it.
You are now ready to etch.
I don't etch a lot of boards at any one time so I got a small jar and made marks on it for a three to one ratio. I use three parts Hydrogen Peroxide (3% solution) to one part Muratic acid (Hydrocloric Acid).
I use just enough mixture to cover the board and a bit more.
Update: I use 40% peroxide now with a 3 part acid to one part peroxide ratio.
The acid is not good to breath and you should not use it in a small enclosed space. There will be a little vapor that you can see. This is normal and just enough to scare you a little each time you open the lid to the acid. Wear rubber dish gloves and even goggles if you're clumsy.
Pour in the mixture and make sure the board is covered. Agitate the liquid over the board to keep fresh etchant one the copper. The liquid will start clear and get progressively more green as you etch.
After a couple minutes you will see the edges of the board clear of copper. If you have a large area of bare copper it's a good idea to mask it off with pen or paint before you etch. You can't really reuse the acid so it's not the same as with Ferric Chloride where you need to conserve your etchant. A gallon of Muratic Acid is only $5, lots of boards there!
When the board gets close to finished you can get ready to wash it off with water. Once you do not see any more copper swish the board around a few seconds more and then wash it off .
Inspect the board to make sure you etched all the copper off. If you need to etch a bit more just drop the board in for a minute longer. The etching is a bit slower now because the acid is weak. If you put in a small splash of Hydrogen peroxide the etchant will work a little more.
If everything looks good then use a bit of acetone and a cloth to remove the toner from the board. If you have some pitting you can use steel wool to buff out the copper so it shines again. Pitting is caused by little pin holes in the toner. Thicker toner deposit on the paper cures this.
Start your drill press!
A drill press is the best tool for the job of drilling holes. Either a dremel in drill press stand/holder or a conventional small drill press. I use an $80 Delta drill press and it seems to work fine. The faster the speed the better the results. My press only goes up to 3100 rpm but if you drill slowly it works well. The fast speed works well to cut and remove the board material. Like a router bit which spins incredibly fast, clean holes are determined by three things. Bit sharpness, speed, and how fast the hole is drilled. ("feed rate")
I use #65 size bits for most of the board and #59 for wires and large diodes and some bigger parts leads. Smaller bits work as well. #69 size bits work for most resistor and cap leads. After you drill a lot of holes the bits wear out . I use high speed steel bits but carbide bits are better. Good and inexpensive carbide bits with 1/8 shanks can be had at Drill Bit City on line.
photo paper toner transfer method
Laser printers and photocopiers (the black only ones) use a black powder type ink which is melted by a fuser on to whatever paper you run through it.
The toner transfer method which we are talking about here must use this black powder toner ink in order to work. The powdered toner is a type of plastic compound which sets on to of the papers surface and is melted to the paper and then when cool it becomes hard again, it's thick and opaque, ideally you will see no light through it. You can feel the toner on the papers surface (don't touch a section that you are going to use because the oils or dust on your fingers will inhibit the transfer).
Color laser printers may work but I would not think so. The ink is thinner and less opaque.
Ink jet printers use liquid ink which is water or some other base. It soaks into the paper and will not transfer with heat. Same thing as if you drew a design on a piece of paper with a sharpie...does not work...at all...
The reason the the toner transfer method works is because you can iron the toner and re melt it. When you put the paper with your toner PCB pattern on a piece of clean copper you are melting the toner with the iron and transfering it from the paper to the copper. Then the copper board cools and you have transfered the image.
Ink Jet Photo paper is coated with a compound which the toner sticks to well and will come off the paper when you soak it in warm water. The paper dissolves and becomes pulp again like when it was made(basically). The coating of the ink jet paper is somewhat crucial to the transfer as it is another layer which blocks the etchant from getting to the copper coated board of your PCB. Laser printer paper may work but I have only used ink jet paper. I would think that the coating used to absorb the ink ject ink is better for transfering the plastic laser toner to copper. as well as how it cleans up with water.
Press and peel blue is a plastic sheet with a blue film over it. The blue film peels off where the pattern you printed is. Very similar in theory to photo paper. Press and peel film is more accurate because the film is finer and peels off easier which makes for cleaner transfers with super fine detail. It'd made for the job at hand, but you pay the price. Personally I can not afford to buy PnP blue so I spend a little more time to make the paper method work for me.
There are many photo papers to use and they all work to some degree. You will have to try them out and vary iron temperature and time ironing. Some have coated backs as well as dual sided papers which you can print on both sides. I would stay away from dual sided paper as you only need and want one side to transfer. Your iron will likely stick to the dual coated paper...Papers with a natural paper feel and backing (uncoated) will come off the best but near perfect results can be had with coated ones as well. I'm taking about the coating used to make the paper feel more like a photographic lab print.
The paper I use is Staples brand Photo Basic Gloss (red package Item# 471865) You can often find it on sale and it comes out to around 20 cents per sheet 8.5"x11".
I have found that using a photocopier with a dark setting works best for me. Just darken the copy it until you get shadows and back off one step. The thickness of the ink is key to getting a nice solid transfer and not getting pitting with the etchant. (small pits where the etchant gets under the toner transfer and eats up your board).
Tips for all photo papers
- Polish the copper clad in two directions with #0000 steel wool to clean off all oxidation and contaminents.
- Iron your transfer for 3 minutes or less over all the board and especially corners. (may vary depending on paper or PnP blue.)
- Use the tip of the iron and press over the whole board alternating between the tip and the whole sole of the irons bottom.
- Cool the board enough to handle it.
- If the paper is coated on the back (shiny plastic like, not neccesarily double sided...) you can rough up the backing after you iron the transfer on the board with a piece of 80 grit sand paper. This will let the water soaking penetrate faster.
- Put a couple drops of dish soap on the papers backing and rub it in.
- Soak the board in hot water from the faucet, no need to boil etc. Let it soak for 30 minutes.. make some tea...have a sandwich...
- The paper should be able to be peeled off and the remaining coating and paper pulp can be rubbed off and cleaned up with a soft tooth brush.
- Keep it soaking if the paper is sluggish to come off.
- I've had perfect results for many boards using this procedure. No flaking or pitting.
Well, that's my take on it...
The materials I use
- Staples brand "Photo Basic Gloss" in the Red package. Item # 471865
- Many papers will work but what you want is a shiny or coated inkjet paper.
- I've used 5 different papers and this is the one I like best.
- Laser printer or photocopier any decent photocopier or laser printer will work. The thicker the print the better!
- Hydrocholric Acid (Muratic acid / pool cleaning acid) one gallon is about $5.
- Available at most hardware stores.
- Hydrogen Peroxide 40% solution Most beauty supply shops have this.
- Acetone. To remove the toner after etching and clean the boards before etching.
- Denatured alcohol works for cleaning and is less smelly.
- Copper clad (1 ounce copper) Fr-4 glass and epoxy board.
- Any copper clad board will work fine. Check ebay as there are some great deals!
- Drill bits. #65-#69 for most general parts. #59 for larger parts and off board wiring.
- If you use small wire like #24 you may be fine with just #65 bits for off board wiring.
- High speed steel works ok but carbide bits with the larger shank are best. Try Drill Bit City.
- Drill press: Any small press should be fine. Faster speeds (3100) or faster are the best.
- Harbor Freight has some inexpensive ones. The prices are around $100 or less.
- Table saw for cutting boards. I already have one and use it for making other things... Dangerous!
- A small band saw is much safer. Pay attention, no distractions.
- Scoring with a razor knife, jig saw or hack saw will work but you need to get your skills down to get a smooth cut.
- Mill bastard file For smoothing off rough edges and cleaning up the lip of the copper side of the board before ironing.
- 80 grit Sandpaper An alternative to using a file. A file is a better tool but sand paper can be used as well. Good for roughing up the back of the ironed transfer to facilitate a better soak off of the transfer paper.
- Reuse the etchant mixture!
- I store the used etchant in a plastic juice container. Add in a little peroxide and acid to charge up the solution and you are ready to etch!
- For a three or four boards just add in a half cup of each roughly.
Let me know if I forgot anything and I'll add to this.