The use of pressure / heat / chemicals to transfer toner printed on various different papers by a laser printer or copier onto the target. This is often used to make PCB's resist layers, however: "I found that toner transfer works on painted surfaces. To improve the appearance of my bots, I give the top side of the finished pcb a light coat of Krylon flat white and then toner transfer. Looks great." Thanks to the Yahoo "Homebrew PCBs" group for much of the information collected here.
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The 'Press-N-Peel' version generally works better, but costs more, than
the 'Press-N-Soak' version. You can get both kinds from Electronics
http://www.elexp.com Press and re-melt works very well if you are careful not to smear.
http://www.elexp.com/pro_npb5.htm (as of 2010/05/13)
Cleaning the PCB stock is critical. Scrubbing with scotch brite pads, bar keepers friend or other light abrasive cleaners is recommended. Avoid anything with oils, "conditioners", or that leaves any sort of film.
Having said that, it has been reported that CitraSolv cleaner (a very effective degreaser and cleaner based on d-Limonene from citrus rind) is an effective toner solvent and works nicely as an surface prep for PCBs. It does leave a thin film, but that film acts to bind the toner to the PCB. Richard Dheiliger reports that Laquer Thinner also leaves a "haze" that appears to help the transfer process.
Dustin reports that after the main scrub and clean with Glass Cook Top cleaner, a rinse in Tarn-X also helps so that may be a good way to "fix" any otherwise good abrasive cleaners which would otherwise leave behind a film.
Pre-etching the PCB stock can help the toner adhear. Some people wipe the copper with Ferric Chloride to "rust" the surface and then just leave it on, others dip the board and clean it off. This provides a rough surface that improves the toners ability to grab onto the copper.
Pre-heating the PCB stock in an oven (e.g. 350'F for 3 minutes) helps the toner stick. Be careful when laying down the paper as the toner will stick and smear if the paper is moved.
Printing When printing, keep in mind that the printers / software may not produce a printout that is /exactly/ the correct size. The traces may be "stretched" or warped in the x or y axis. It's good to have a PCB program that allows fine scaling of the printed size in either dimension. The alignment of the printer can also be adjusted by a competent service tech. This issue can, in extreme cases, cause individual components to fit poorly but most often the error is small enough that it only becomes apparent when you try to CNC drill the holes; when one side of the board is lined up in the mill, the other side will be off just far enough to cause the machine to drill outside the pad.
If you media is very thin or curly (e.g. magazine or parchment paper) or hugly expensive, you may wish to tape it to a regular sheet of paper with kapton tape along the leading edge. You can print the pattern once on paper, then use that as a guide to tap the media in place over the printed area, and feed the same stock again to ensure it will print exactly where expected.
Methods of Transfer by applying Heat and Pressure:
"What makes GBC the only laminator manufacturer that works with Pulsar process is because of the way they redesigned the ordinary pouch laminator heaters. The ordinary laminator uses two parallel heating plates after the rollers to seal the pouch. GBC mounted two curved heaters, one above the top roller and one below the bottom roller and radiate heat into the neoprene coated rollers kind of like a rotisserie chicken cooker!"
Jim KI6MZ says:I got a 1 inch thick piece of steel (4x5x1 inch) and lapped it to make a very flat surface, attached a thermo couple to it. Using a hot plate to heat the iron block to to the target temperature [ed: where the toner melts; for this toner: 320'F] then placing this on my PCB/toner image sandwich and clamping it with a toggle clamp with about 400 pounds of pressure for about 1 minute (20 pounds per square inch). This gives me consistent results. ... For very fine pitches, I use a [pre-heat] temp of about 280 degrees (this will just tack the image to the copper) then I take this tacked PCB/toner/paper sandwich and place it on the hot plate and raise it to the toner melting point (without pressure) ... this will cause good adhesion of the toner to the copper with minimum image spreading.
Howard Payne says: "What i did was get an old cloths iron and took out the thermostat and bolted it to the roller casing (same place where a fixed 120c thermostat was mounted) wired it up and set it to about 180c (my toner is HP black)."
Fast Eddy says: "I print out the traces on magazine paper (which will tend to transfer the ink from the page) or glossy inkjet photo paper and tape it to the copper clad board with the blue delicate surface painter's tape and run it through a laminator a couple of times to stick it down to the board. I then pop the board directly into a toaster oven *with the paper still on it) at about 375F for 2 or 3 minutes to melt the toner and heat the board all over, then pass it through the laminator a couple more times before it has time to cool."
Lee Leduc says: "I took a sample of the printed paper and exposed it to acetone fumes for 20 minutes in a sealed plastic food container. The toner became slightly tacky to the touch. I ran the paper and pcb through a GBC laminator 8 times" Lee then soaked and peeled the paper leaving the tonor on the copper board. This was done with a Brother HL-2240 laser printer
Chemical Transfer Methods
Super Glue: If using Parchment Paper or other silicone coated stock (see above) then you can transfer without heat and only moderate pressure by wiping a thin layer of super glue onto the metal, and immediately pressing the baking paper with printed design onto the metal surface. The toner will stick to the wet super glued metal, but the paper will lift off after the glue has dried.
Rod^ says:"Too much glue, and or too dark a toner printout will cause the toner to muddy up, so use a little glue on a Q Tip cotton swob. If you experiment, within a few minutes you can hit upon the correct, light print, and light coating of glue. I go for more of a grey printout, rather than black. Do not wipe the glue onto the baking paper, wipe it onto the metal....thin wipe with no excess puddles.
Do not wait for the glue to dry, but apply your design immediately. Burnish with the back of the finger nail, or a bone burnisher, etc., and no need to press too hard. Watch the design leave the paper using microscope or magnifier. When you sense the toner has transferred, you may wait a few minutes to ensure the glue has set. If things go wrong, a quick wipe with acetone cleans the metal down for a second try. If you get partial transfer, your glue may have dried too soon, or maybe you need a little more glue. Use the thin watery super glue, and make sure it is like water, it has a shelf life and sometimes it is already hard or thick from too long on the shelf at the store where you bought it. It is about 20 times cheaper by the once compared with 1 gram at the store. Keep it in the freezer for longer shelf life of about 6 months."
Blender Pen: Jesse Willis says: "What I did was swing by my local art store and pick up an Eberhard Faber Design Art Marker, Broad Nib 311 Colorless Blender (only about $2 US). With this, you simply photocopy the circuit you wish, and then lay the photocopy face down on the PCB. Run the marker over the back of the photocopy, and the image transfers to the copper." If anyone has a source for these pens, or has tried another brand of Colorless Blender Pen, please let us know?
Re-Melt: Re-heating the board after paper removal will allow the toner to re-flow and fill any tiny holes or cracks that would otherwise allow the etchant to penetrate the resist.
Touch-up: Check for traces that are broken or large pads / fills that haven't filled in well. Some laser printers have a difficult time filling in large areas. Using crosshatched fills rather than solid may avoid this issue. Correct these errors with a fine tip Black Sharpie^ (only the black seems to hold up).
Check for smudges, smears, or just places where the toner has spread too much and closed in the gap between traces or pads. Use a needle or narrow tip knife to scrape away the toner and expose the bare copper underneath.
Etching the board is the final step. See: PCB Etch, PCB Echant, Printed Circuit Board fabrication
Removing the toner: Acetone (e.g. Nail Polish remover) seems to be the only thing that takes toner off quickly and cleanly. It's a nasty chemical and shouldn't be used in a closed space. You can put the PCB and some Acetone in a ziploc bag, then soak it while rubbing the board through the plastic to keep your exposure to a minimum.
It has been reported that CitraSolv cleaner (a very effective degreaser and cleaner based on d-Limonene from citrus rind) is an effective toner solvent, but this has not been extensivly tested.
Laser printers made by the "Brother" brand apparently use a toner formulation that melts at a much higher temperature than others; about 187C (370F). As a result, it can be harder to transfer the toner to the PCB. Also, the toner used in older Brother printers, such as the HL-2400CN, appear to have an oily consistency which prevents adhesion of the toner to the PCB. Newer Brothers, such as the MFC-9420CN work ok as long as a higher transfer temperature is maintained. +
HP and Lexmark toner melts at 170 - 180°C (338 - 356°F)
Marion D. Kitchens says:
I have had good results as follows: Using a plastic film intended for the purpose, print a negative image with a laser printer. This will iron onto clean copper nicely of you are careful. I find it works better if I heat the copper board on the iron, and then roll the film sheet onto the moderately hot copper. I use a roller from the photo lab, and roll with light pressure. Too much pressure will smear the toner. I have been able to get copper traces between the 0.10 pins of IC's this way. Good luck...
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