Toner transfer method for making PC boards is very practical and economical. The use of heat for the transferring is not. Large boards expand with heat (more than the laser print) and heat is applied to the top of the toner and not to the bottom contacting the copper layer. Too much heat melts and deforms the toner, too little heat and it won't adhere uniformly. In this Instructable I will describe a very simple technique I've been using for over 15 years. It is very fail-proof and involves the use of only 2 common chemicals : Ethyl Alcohol and Acetone. You can replace the Acetone with Toluene or Xylene, but you will have to experiment with the proportions.
Step 1: Toner Is Inert to Alcohol
Alcohol is volatile but neutral to toner or paper. Its purpose is to dilute the Acetone.
Step 2: Acetone Reacts With Toner
Acetone, (pure, not nail-polish remover) dissolves the toner immediately.
Step 3: The Formula
Experimentally I found the best alcohol-acetone proportion is 8:3 (8 volumes alcohol + 3 volumes Acetone) Acetone will "soften" the toner just enough to make it "sticky" but not dissolve or blur.
Step 4: Storage
You can store the preparation for a very long time but the container must be absolutely airtight. Acetone is much more volatile than Alcohol so exposing to air will degrade acetone concentration. The container should also survive the action of acetone. If plastic, it should be HDPE(high density polyethilene, often used in kitchenware)
Step 5: Cleaning
This step is the same you would do for any other toner tranfer method.
Step 6: Procedure
Pour the solution on the board (not on the print) and quickly spread to cover all its surface (quick!, acetone is volatilizing). Place the print on the board and center it in place without pushing down. Now press gently down, fully contacting the solution. Wait 5-10 seconds before finally pressing down to adhere to board (only perpendicular pressure). During those seconds, acetone is reacting with the toner rendering it "sticky". Use some kitchen paper to spread pressure evenly and absorb excess liquid. Let dry, and dip in water.
Step 7: Release the Paper
After a few minutes (don't be anxious) peel the paper off starting from a corner. There should not be any toner on the paper. Rinse the board in water to remove any remaining paper particles.
Step 8: Etching
Step 9: Large Boards
For larger boards, I place board and print between two blocks of wood and press together with a C-Clamp. Place a layer or two of kitchen paper between print and wood to distribute pressure and allow for evaporation.