Before you begin, plug in your clothing iron so you don't have to wait for it to heat up, this is where the fun begins!

In this step, consider how many boards you would like to do. If you purchased a board to fit your layout exactly, go straight to cleaning the copper. If you bought a big board, cut it to the size of your layout(s). If you do this with a band saw like me, make sure you clean up the edge of the cut from all the rip-out. You want the surface of the copper to be as planar and even as possible. Clean the surface of the copper with steel wool. This will remove oxidation from the copper and provide a good bond with the toner from your print out.

Once you know for sure your layout is right (that is, you know this resistor goes to the base of that transistor, etc.), or you trust the layout you found, it's often helpful to do a dry run with regular printer paper. This will allow you to see if the pad spacing between device leads came out right. There is a lot of software out there which may not do the correct sizing to your printer, and this is not something you want to find out once you're done etching! Once you're sure the printer will deliver the right pattern, do a print out on the photo-paper. Examine the quality of the print and make sure the toner is even.

NOTE: I like to stuff as many layouts on one sheet as possible, even the same layout repeated for all those OOPS moments (ALWAYS put enough spacing between layouts to accommodate the width of a saw blade). Remember, at this part of the process, everything is still fairly flexible. A nice software tool I use to add multiple layouts together is Inkscape. It's a vector based drawing tool which is important when you copy big chunks of a .PDF (This is extremely convenient to use with EAGLE because you can only export your layout as a .PDF).

It's helpful to cut out the toner pattern on the print out. I like to match the print out to the size of my copper board, this way I know the toner is centered on the board and nothing is hanging off the side. Remember, you are going to iron, and the copper, photo paper, and ironing surface WILL GET HOT. Find a flat, heat resistant surface to do it on, and most importantly, be careful not to burn yourself. My work bench has a rugged marble top which works great.

With all this in mind, place the print out INK SIDE DOWN onto the copper. Iron directly onto the back of the paper. The idea is to use a lot of flat, square pressure. You want the heat of the iron to distribute evenly across the copper. Don't worry about the back of the photo paper, it gets peeled off later. I like to start on one end of the PCB, just to make sure I get one portion of the pattern to stick. If you're dealing with a large PCB, move the iron about an inch every few minutes across the board, always applying pressure. Once you know the print out is sticking, you can start to use ironing techniques like flat, quarter rotations back and forth, and flat longitudinal motions. Again the board gets really hot so you might find yourself ironing one end while holding the cooler end steady. The transfer process takes as long as needed. Periodically check the edges by peeling back the corner of the print out to see if the toner is sticking, and the paper is separating. You can bet if the edges are sticking well, the center is sticking well too. I found that 4x4" boards take me about 10-15 minutes to get a good transfer. With some photo paper, you might start to notice the toner pattern developing on the back of the from the iron metal, kind of like a stencil. This is a good rule of thumb that you're toner transfer is close.

I accomplish this step using my etching container. Fill the container with hot, soapy water and submerge the board/ paper transfer. Allow the paper to saturate with water (about 5-10 minutes). After the paper is soaked, it usually peels right off, leaving the toner pattern stuck to the copper. This step is highly dependent on the grade of photo paper and you may only get half to peel off. Successive soaking may be necessary to get all the paper off. I use my thumbs as well because the toner-copper bond is much stronger than the toner-paper bond.