Printed Circuit Boards by Toner Transfer
I took a short class in PCB techniques at Workshop 88 last summer and since then have been accumulating the necessary kit to make my own boards. Jim Williams taught the class and he uses a Hydrochloric Acid/Hydrogen Peroxide mixture to etch the copper. These evil sounding chemicals available at most hardware stores are actually more benign than the Ferric Chloride or Ammonium Persulfate from Frys. The Peroxide acts as an oxidizer and is used up pretty quickly leaving the HCl and copper chloride. You can bubble air through the mixture, which converts the copper chloride into cuprous chloride which by itself is a good etchant. So the brew is more or less renewable.
I decided to try the laser printer Toner Transfer method for my first project, a modified Arduino shield that supports an MCP2515/MCP2551 chip set for a CAN buss network. My version is a riff on work done by Kevin Smith. His web site provided an Eagle schematic and board as well as example software and libraries to use the 2515. I modified the Eagle files, removed some parts and printed the result two up with my Lexmark 4039 10+ laser printer. The Lexmark can be set to print an extra dark image. This is the result:
Top right is one half of the two up printout from Eagle. Top left is one of the patterns ironed onto a piece of single sided PC board material, the bottom right image is a board fresh from etching and drilling, bottom left is an assembled board mounted shield style on an Arduino clone.
There are many sites on the net where you can research the toner transfer method. My technique is to crank the print density on the 4039 to up to “dark”, then print on paper salvaged from a slick magazine. The classified pages from a “Fine Woodworking” worked well. I put the printout image side up on a table, then carefully place the precut single sided PC blank on top of the image. Then fold the paper up over the edges of the board. Now put the blank foil side up on a piece of plywood that forms my ironing board, place the printout over the blank using the fold lines as a guide. Iron at high heat for about two minutes. Remove the Iron and roll the paper firmly with a brayer while it’s cooling.
The printout is now melted onto the board copper. trim the paper leaving about a quarter inch all around, then soak in warm soapy water for a few minutes. The top layer of printout paper will peel right off, then gently rub the surface with fingers. The remaining paper will slough off. Finally a very gentle scrub with a soft toothbrush to make sure the paper residue is cleaned out of the pad holes.