Step 3: Iron It On
With the two paper sheets taped together, turn on your iron to the highest setting. Also make sure there is no water in it if you have a steam type iron. Now, take your sheet of copper board and slide it carefully between the two sheets. See pic below. Position the copper clad board as desired, and once the iron is hot, place the iron on the paper and press hard. It takes some practice to get the hang of ironing on the toner, but just press hard and wiggle the iron over the whole board while taking care not to move the paper relative to the board. Once one side is ironed to your satisfaction, then carefully flip the whole thing over and iron the bottom layer. One thing to remember is to clean the board carefully with a cotton ball or old sock soaked in isopropanol (rubbing alcohol) before ironing to remove any finger prints or grease.
Once you are done ironing, cut the paper around the board if desired, and drop the paper and board into a container of water to soak the paper. Let this soak for about 10 minutes. With the cheap glossy laser paper from Kinko's the time is much shorter than the high quality inkjet photo paper. Once the paper is soaked, peel the paper off both sides. This should leave the toner and a thin layer of the paper along with the glossy stuff on the copper board. Using your thumbs or an old toothbrush, carefully rub off the extra paper pulp and junk on the board. See pic, below showing a board with half of the pulp rubbed off.
Once the paper pulp is rubbed off, carefully inspect the traces and features on the board for small imperfections and stuff that will cause problems later. Key areas to pay attention to are closely spaced traces and pads where it is easy for paper or glossy coating to bridge and keep the copper from etching. Also, you can achieve very fine pads for doing TSSOP, QFP, and other fine pitch packages using the toner method if you carefully scrape between pads using an Xacto knife or similar prior to etching. During ironing, the toner tends to smear slightly, so very fine pitch pads tend to mush together. Using the knife, you can scrape between the pads or traces to make sure the copper will etch between. If you are careful, there is no reason you can't get 800 micron or even 500 micron pitch pads.