Jmengel shows another way to make two-sided PCBs at home —
This instructable assumes that you know how to generate a layout file using Eagle PCB or similar layout program. I use the toner transfer method of making PCB’s (printed circuit boards) much like many others. The basic idea is to use a glossy paper, print the PCB design on the paper using a laser printer, and to use a hot iron to transfer the toner to the copper. I use the glossy paper that they have behind the counter at Kinko’s. Go to Kinko’s and ask for some sheets of their glossy laser paper, which is really cheap (about 5 cents a sheet). Some people advocate using glossy inkjet photo paper, but I think this is a waste and the cheap glossy laser paper comes off easier.
Anyway, once you have your design and paper, you will need to print the design. The key here is to mirror the top layer so that it will come out correct once transferred to the copper board. It can also help to include alignment marks (the T shaped things in the pic) beyond the edge of your PCB to help you align the two layers.
Two sided PCB using toner method – Link.