printed circuit boards make it easier to develop complex circuits, and become essential when working with surface mount components which cannot be soldered to stripboard. Laser printers make it easy to create professional-looking printed circuit boards using the toner transfer method. The board design is first printed on toner transfer paper using a standard laser printer, and the toner is then transferred to the copper board using a hot iron. The board is etched, leaving copper traces under the toner, which is then removed with acetone.
Instructions
1 Create the layout for the PCB using a PCB design package. Free packages are available online, or a free trial of a professional program can be used. For simple designs, the traces could be drawn by hand on paper and then scanned in, or drawn in a graphics editing package.
2 Print the image onto a normal sheet of paper to test whether the design is correct and properly sized. Set the laser printer to its darkest setting, at least 300 dpi and with economy printing disabled. This increases the amount of toner used by the printer, to enable a better transfer. Check the test print is correct, with clean traces and a clear gap between each trace. The board design should be the mirror image of how the design should appear on the copper once etched.
3 Print the image on toner transfer paper. The paper normally requires you to print on a certain side, so check the manufacturer's instructions and make sure it is inserted into the laser printer the correct way. Trim the paper after printing, leaving a small gap around the edge of the board, as toner right at the edge of the paper may not transfer properly.
4 Clean the copper board with detergent or alcohol to remove any dirt or grease. Older boards with a dull surface may need scrubbing with an abrasive pad. The surface of the copper should be clean and shiny, indicating any surface oxides have been removed. Handle the board by the edges, as touching the board can leave a fingerprint that the toner may not stick to. The toner transfer paper should then be placed onto the copper board, with the toner side facing the copper. Align the paper so it is straight and perfectly smooth.
5 Iron over the toner transfer paper with an iron heated at 275 to 325 degrees Fahrenheit. Do not turn the iron to its maximum setting, as it may overheat the toner, causing smudging. Apply even pressure to the board, and don't press with too much force, as this may smudge the toner. Iron over the board for 2 to 3 minutes, then remove the iron and allow the board to cool.
6 Soak the board in a bowl of water to free the toner transfer paper, leaving the toner behind. Allow to soak for 10 minutes and then peel off the paper. Any remaining paper can be removed by gently scraping or soaking for longer. An old toothbrush can help to scrub the paper from the board. Inspect the traces when the board is clean and dry. Unintentional gaps in the toner can be filled in with a permanent marker or PCB pen.
7 Etch the board in a plastic tray filled with enough ferric chloride solution to cover the board. The solution should be warmed before use by placing the bottle in a larger container containing hot water. After 5 minutes, check the board regularly, as the copper will be etching away. Wait 30 seconds after the copper is no longer visible, then remove the board from the ferric chloride and wash in plain water. Wear gloves through the entire process, as ferric chloride is corrosive and will stain skin.
8 Remove the toner remaining on the board using acetone. This will reveal the clean copper traces forming the circuit.
