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.

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

Transfer methods

• "press and peel"
• "press and soak"
• Press, re-melt, and peel

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

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

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 inproves the toners ability to grab onto the copper.

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 tonor to a PCB. Placing a large dowel or rolling pin under the PCB allows the pressure to be "focused" on one area at a time for a more consistant and stronger transfer.

Advantages:

• Simple: Print, transfer, remove the media, etch, clean, done. The only thing that might require some tinkering is the transfre 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 consitantly transfer to the PCB stock can be a "magic" process. Some never have any problems, others can never get it to work consistantly.
• Most laminators must be modified to allow a full thinkness PCB to pass through.

See also:

• http://catmacey.wordpress.com/projects/making-pcbs-with-simple-tools/ A very low tech, but quite sucessful 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 Pictoral, 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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