Here is the toner transfer method I came up after wasting days on pretty big research.
This instruction is the result of pretty big research and testing of toner transfer and photoresist methods I have completed within two weeks in late 2008.
Here are the links to the research:
Researching Toner Transfer method of PCB making (part II)
Researching Toner Transfer method of PCB making (part I)
Here you can find a complete step-by-step procedure and list of materials for making a PCB using toner transfer method. I could archive 0.12mm tracks and 0.2 gaps (0.15 maybe possible, did not try it) before etching stage.
Another big advantage of this method is that it does not use any stinking and dangerous chemistry. No acetone, spirit, solvents. No more of that stuff! My wife is very glad now :)
List of materials and tools:
- Printer HP LJ 1200 (can do 600dpi max), refilled cartridge with noname cheap toner.
- Paper Lomond 120g/m2, glossy, with improved coating, #0102053.
- Small portable iron.
- Rubber wallpaper roller
- Rubber (thin) gloves
- Some POWDER cleanser (not liquide or gel or anything) with oxalic acid (like Comet, BarKeeper's Friend and Zud)
- Some creamy cleanser which is very good at cleaning grease (fats). The copper must squeak under your finger after cleaning with this stuff.
- Usual hand dishwashing cleanser.
- Tough brush.
Printing the layout
Set your printer to max dpi and at max toner density (usually it is the setting to print on transparent media). Feed the paper sheet through the printer without printing anything exactly one time. This will give it good thermoshrinking without damaging its toner transfer abilities too much. Remember: two times - bad, zero time - bad, one time - good! It is important. After that print two or three layouts on the same sheet of paper and choose the best one. Ideally you should scan the sheet and measure the tracks, gaps and distortions and choose the best one. The layout is now ready for toner transfer. DO NOT touch its surface with your finger. Grease is your worst enemy!
A small note about new laser printers. It seems like newer printer which can print at 1200dpi try to conserve toner so much, that it does not even get very dense at any settings. So, if you really don't need 1200dpi set the printer to 600dpi. But who knows, maybe 1200dpi works fine for your printer. Try it and see for yourself.
Preparing the copper laminate
If the copper is really greasy and old then you should polish it first or clean with fine sandpaper (1000-1200), but that's unlikely. Put your gloves on (they must be thin, so you can feel what you do). Clean the copper with dish cleaner first. Then clean the copper with powdered cleaner using some tissue. It must contain oxalic acid (hurts you skin when it gets onto it with water) which removes the oxidations. Also, this powder cleanser makes micro scratches which are good for toner transfer (does not allow the toner to flow too much and allow it to stick to the board). The copper must look really bright after this (but not like a mirror, mirror is NOT good). Clean the laminate with HOT water (cold water may contain chlorine, which is bad for pcb). Then clean it with the creamy degreasing cleanser. After than the copper must be very bright and clean and squeak under your fingers. The water must not roll off the board. It must stay on the surface evenly spread out. If you have problems here with the water rolling off then the board is still dirty or too mirror like. Take some household soda and thoroughly clean the board with it then clean it with the degreaser again. This should solve the problem.
Dry the laminate with hairdryer until it is completely dry. While doing it run the water off the board, so you will not have any spots from water salts on the copper. DO NOT touch the copper with anything!
The board is now ready for toner transfer.
Choosing the right iron temperature is covered here: Choosing the right iron temperature for TT
Turn on you iron, set the right temperature and leave it to heat up properly. Take the iron and turn its bottom side (hot shoe) up. Put the copper laminate onto it. Let it lay there for some time (10-20 seconds). Touch the edge of the laminate - it should be hot so you cannot touch it for more than 3 seconds. Shake off the laminate onto the surface when you will iron it. It should be even, smooth and firm surface. Usual ironing board or smooth wood is fine.
While the board is still very hot very carefully put the layout on it toner down and stroke it with your fingers. Usually it sticks to the hot board right away. It is the photolayer that sticks, not the toner.
Now take the iron and iron the board for 1 minute. Move the iron evenly and slowly (10cm per 4-5 seconds). Do not push it to the board to much. Too much is not good because it will spread the toner too wide. Now here is the quick part. Put the iron away (don't turn it off), take the rubber roller and roll it firmly pushing to the board from one side to another. You must cover the whole board when doing it. Do it for 5 seconds. Now take the iron and continue ironing. Repeat this cycle (iron-roll) 3-5 times (the larger the board the more repetitions).
Leave the board to cool of for 3 minutes.
Wetting and cleaning
While the board is cooling off poor hot tap water into some container (you can use you favorite deep dish - there is nothing toxic here). Hot water is also good because the board will not experience any temperature shock, which is bad. Put the board into the water and wait for 10 minutes. Do not any detergents, soap, dish cleaner, etc! It is known that some of them partially dissolve toner or make it soft!
After ten minutes the paper will barely hold to the board (that is if you choose the paper I have chosen). Peel off the paper, take out the board, and wash it once again in hot tap water. Dry with hairdryer at LOW temperature (you don't want to melt the toner now).
When the board dries you will see a whitish photolayer. This photolayer is DA THIN! The toner itself is very porous and because if this when you etch the board the fills become pitted. Photopaper has this photolayer which seals the pores in toner and saves the day.
However, the same photolayer does give some headache. It fills all small gaps of 0.1mm and most gaps of 0.2mm and makes track edges very rough with unpredictable width. The old way top clean it was using a needle, but I have found an easier way. Fully dry the board. It must be really really dry. Now the photolayer not bound to the toner becomes very fragile. Take you tough and rough toothbrush or special brush for pcb cleaning and give the board really good cleaning. The cleaning must be strong, but not too strong, so the toner comes off.
That's it! The board is ready for etching!
I etch in very hard ferric chloride solution (1:1) at 40-50C manually rocking the container. It takes about 10 minutes to etch the board. You MUST do fast etch, otherwise the tracks will get etched on the sides and will get narrower (but who knows, maybe it is what you want, but the process is hardly predictable).
It is important to keep the solution warm and mix it. You can take the board out of the solution anytime to see how thing are going. It does not hurt the process at all. When you see the last copper disappear take the board out and wash it in hot tap water right away. I know, copper in the sewer system is no good, but I don't see any other way to stop the reaction quickly.
The other way you can etch the board very fast and produce less waste can be found here pulsarprofx. I did not use it yet (as of 15th February 2009) but I am sure it is the way to go!
Now you have to remove the toner on the tracks. As I said, I don't use any stinking solvent. I just take the same powdered cleanser, put a small heap on the board, add a little water, and rub it thoroughly with a tissue. The toner comes off pretty easily. Not like with acetone, but it does not stink, clean the oxidation after ironing and readies the board for tinning with Rose's alloy and glycerol.
By the way, for VHF/microwave PCBs removing toner with acetones can kill the board, because dissolved toner actually stays in many places and is almost invisible. People have reported unworkable PCBs after that. After removing toner with sandpaper (yes, this is also and option, but I don't like it) there were no such problems.
If something went bad
Clean the toner thoroughly with the powder cleanser, do the same prep as before, print a new layout and do all over again.
Here is the 3200 dpi scan of the board before etching (126 pixels per 1 mm), the smallest track width is 0.12mm, the smallest gap is 0.2mm (0.1 is dead filled with photolayer). The detail level is ABOVE of what dry photoresist method can offer. I have tested it too, believe me. Download scan.