Toner Transfer PCB Etch Resist

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. I found that toner transfer works on painted surfaces. To improve the appearance of my bots, I give the top side of the pcb a light coat of Krylon flat white and then toner transfer. Looks great.

Toner Transfer media

• Gootee paper (available from Staples)
  • http://www.fullnet.com/~tomg/gooteepc.htm
• label backing (this is typically TOO slick and the toner will break or fall off before you can get it on the board.)
• glossy papers (e.g. a page ripped out of Time magazine, etc...) Many people report success with this method. The paper can be soaked or brushed off.
• Laser transparency film. Some people have reported excellent results with this, other have reported the toner will not release at all. Try 3M #cg5000
• Clay coated InkJet papers. These may or may not be safe for a laser printer, but the advantage is that the clay will disolve in water after the transfer is complete.
  • "Glossy Ink Jet Paper" from Royal Brights, 108 Main Street, Norwalk, CT 06851 phone 1-800-526-4280
• Homemade release paper

Toner Transfer methods

• "press and peel" Using special label backing paper
• "press and soak" Using release paper or just disolving the paper itself.
• Press, re-melt, and peel or soak.

The 'Press-N-Peel' version generally works better than the 'Press-N-Soak' version. You can get both kinds from Electronics Express:
http://www.elexp.com/index.htm Press and re-melt works very well if you are careful not to smear.

Also, checkout the Desk Top Fabrication system by DynaArt Designs. They have a catalog/flyer they can send, call 813-524-1500.

Cleaning the PCB stock is critical. Scrubbing with scotch brite pads, bar keepers friend or other light abrasive cleaners is recommended.

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.

Methods of applying Pressure:

• GBC laminator
• The fuser section of a laser printer can be removed and converted to re-melt and press toner onto the target panel as long as it is very smooth and can be made to pass between the rollers.
• A standard clothing iron can be used to press and heat transfer the toner to a PCB. Placing a large dowell or rolling pin under the PCB allows the pressure to be "focused" on one area at a time for a more consistent and stronger transfer.

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.

Removing Paper:

• Soaking in warm water. Some papers seem to just float off the board without effort after about 20 minutes of soaking. Excellent results have been achieved with clay coated inkjet papers. Of course, the best for this is the commercially available "press and soak" systems
• Gently scrubbing wet paper with a toothbrush, sponge or your thumbs can help.

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.

Etching the board is the final step. See: PCB Etch, PCB Echant, Printed Circuit Board fabrication

Advantages:

• Simple: Print, transfer, remove the media, etch, clean, done. The only thing that might require some tinkering is the transfer step.
• Cheap: Assuming you have access to a laser printer, the transfer media is low cost (can be free) and you may get away with just a clothes iron to do the transfer. Even with a laminator, the cost isn't much.

Disadvantages:

• The pressure involved often causes the transfer media to stretch or expand, resulting in a small, but sometimes critical enlargement of the resulting pattern. This typically prevents toner transfer PCB's from being CNC drilled. It can also cause alignment problems with larger double sided boards. Direct InkJet, and Hybrid InkJet / Toner offer more repeatability, but the best for this is Optical
• The pressure involved often causes the traces to expand, limiting the minimum trace width and space between the traces that can be achieved. In general 10 mil traces and spaces are the limit.
• Getting the toner to consistently transfer to the PCB stock can be a "magic" process. Some never have any problems, others can never get it to work consistently.
• Most laminators must be modified to allow a full thickness PCB to pass through.

See also:

• http://www.pulsarprofx.com/ PCB FAB in a box.
   
  the "green' film is a standard heat transfer foil. You have probably seen the gold version used to hot stamp stamp jewelry boxes. If you remember the early days of laser printers, before inkjets came out, you could buy (and still can buy) "laser foil" to add metallic colors to certificate.
  
  The release paper is Dexatrin coated stock.Dextrin is a starch used in papermaking as a sizing / coating on paper to bind it together and make the surface smoother.
  
• http://forums.makezine.com/comments.php?DiscussionID=1825 There is a link here to a PDF by Triston J. Taylor
• http://catmacey.wordpress.com/projects/making-pcbs-with-simple-tools/ A very low tech, but quite successful method.
• http://www.aracnet.com/~gpatrick/ George H. Patrick, III PCB Environment, Base Materials, and Processes; Trace Width Table, Calculator, and Spacing; Hardware and drilling information.
• http://myweb.cableone.net/wheedal/pcb.htm Pictorial, step by step. Very nice.
• http://www.fullnet.com/~tomg/gooteepc.htm Tom Gootee and his rambling, but very good, site on the subject.

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