Homemade PCB with toner transfer method

Make printed circuit boards at home using toner transfer method. How to print and what paper to use for copper layer and silkscreen.

The toner transfer method is a cheap and easy way to make your own printed circuit boards (PCBs) at home. A laser printer is used to print the design on paper. Not all paper types are suitable for this kind of usage. The paper is placed with the printed side over the copper side of the circuit board and then the whole thing is heated. Most people use with good results a common iron, but if you have a laminator, use it instead of the iron. When heated, toner melts and sticks to the surfaces. The idea is to make it stick to the copper layer. After heating, the board is submerged in water and the paper should be easily peeled off from the copper side. A good transfer means no toner remains on the paper. Once this is done, the board can be etched using whatever method you want (ferric chloride for example).

This method is widespread among hobbyists because is cheap and easy. However, for some, the results are unsatisfactory and variable. I will share some of my experiences with this method.

Homemade PCB with silkscreen

The first requirement is to have a PCB design. It can be made in EDA CAD software (for example KiCad, Autodesk EAGLE, Express PCB). The example used in this post has been designed in KiCad because this is a free cross-platform EDA suite (schematic capture, PCB layout, 3D viewer). The first time, I got very confused about mirroring the design before printing. Well, in all CAD tools I know, you design the top layers normal and the bottom layers mirrored (the PCB is transparent - the traces are drawn in see-through mode). So, the following rules apply:

• bottom layers (copper and silkscreen) must be printed as they are in the CAD software. The result will be a mirror of what you see when looking at the real PCB. If designing a single sided PCB, there is only one copper layer and that is usually the bottom one when working with through hole devices;
• top layers (silkscreen and copper) must be mirrored because when you design them they are not mirrored. For surface mount devices, you place parts and draw copper traces on top layer. In this situation you have both silkscreen and copper on top and you need to mirror both when printing.

Let's make a test. Write something on the bottom copper layer and then on the top copper layer. You will see that the bottom text appears mirrored. Try this with other layers too.

Top vs. bottom layers (green text in on bottom layer while the red text is on top layer)

An important aspect of printing PCB designs is the real size. You must make sure the printer does not apply any zooming or shrinking to your design. If you are uncertain about your printer is always a good idea to draw some lines in the CAD software at a known distance (use the grid available in software), then print the design and use a ruler to measure that distance on real paper. If they don't match, you need to apply a correction factor when printing. As long as you select To Scale, 1:1 or 100% when printing, this shouldn't be an issue.

Make sure you select individual layers when printing. You don't want the silkscreen overlaid on top of the copper layer. Also, I find it better to print very small drill marks or no drill marks at all. There is no need to etch the area of a hole. More, if you etch a very small area (small drill mark) this could help you if you make drills with a hand tool. The drill tip will slip into the small depression created in the copper layer (the etch mark) and holes will be centered with ease. So, I prefer to print designs with small drill marks. If you own an automated drilling machine (CNC) do not print any drill marks. If you're using KiCad, you have this option in Print and Plot dialog windows.

You already know the printer must be laser type. If you have large areas of copper it is recommended to set toner density to maximum (the printer will lay more toner on the paper). You can't use normal paper. I used with great success special paper which has a glossy side (on this one you print). This paper does not absorb toner and it does not stick to the copper. You may try with other glossy paper types. One that could work is the leftover peeled from auto-adhesive wallpaper (but it's not standard size and it jams too easy).

PCB design printed on special paper

You should know that this paper is very thin and once it passes through the printer it has a tendency to curl and you cannot feed it again to the printer. You can cut it in half to make A5 sheets for small projects. It is also useful to print multiple layers on the same page. To do this make plots in SVG format (KiCad can do this) or 600 DPI lossless TIF images, then drag them in Inkscape over an empty page. Neither resolution or real size get altered and you can print straight from Inkscape.

When I inserted one sheet of this paper in the tray, the printer recognized it as "vellum paper". Avoid touching the glossy side of paper before and after printing.

Prepare board by cutting it a few millimeters larger than your PCB design. Clean it with some alcohol, then using fine grit sandpaper (> 500), make a few linear movements in perpendicular direction. This will significantly improve toner adherence to copper. Make sure board edges are well sanded (after cutting, a raised copper edge appears). Place the printed side over the copper side of the raw board and keep it in place with some adhesive paper.

Iron the paper over the copper layer. Apply uniform pressure and make circular moves with the iron with great care not to move the paper until it appears to stick to the board. The iron should have a temperature of 150 ... 180 degrees Celsius (for the paper I used). When toner melts, it will appear to you that the paper sticks to the copper. Well, only the toner does that. After a few circular moves with the iron, take the PCB-paper thing and drop it in water. Some say you should wait for it to cool, but I usually drop the PCB in cold water just after I finish heating it. Move your finger over the paper to make sure the water soaks it and let it for no more than a minute to cool. Take it out and slightly peel the paper starting at one corner.

If you applied too much pressure or heat, this kind of paper will begin to stick to the copper and you can't peel it off. Otherwise, if heat was not sufficient, the paper will peel off easy, but toner will remain on it.

After peeling off the paper: the toner print on copper

This was the result for me. There are some small and unimportant imperfections where toner didn't stick to the copper, but overall the print looks good. This needs to be etched. I used ferric chloride (40% solution). Remember to use a plastic container. To speed up the etching process you should continuously move the container with the PCB soaked in chloride. Slightly heating the chloride also speeds up the process, but be aware of fumes it may generate. Heat it by placing it in hot water, not directly on heat source.

Check often the progress of etching. It will take a lot of time until you begin to see through the board, but once you see areas without copper the process will appear to speed up and you're almost done. Do not leave the PCB in chloride unless there is copper to etch. It will eventually pass through toner and etch tracks too. Feel free whatever etching method you have available.

Etched PCB with toner over tracks

After etching, wash the PCB with plenty of water, then use a harder sponge to clean toner. Leave it in water for a few minutes to get rid of all the etchant. Afterwards, you could also use acetone, alcohol or cleaning products. Avoid sand paper. You don't want to make tracks thinner.

Copper tracks after cleaning the toner

Now, all it remains to do is to drill the holes. The toner transfer method can also be used for printing the silkscreen. It looks good although it's not very scratch resistant. Spraying some incolor varnish on it is not a bad idea. Using the same method (obviously without etching) I created the silkscreen shown in the top photo.

To prevent copper oxidation, I recommend covering the tracks with a mixture of rosin flux dissolved in isopropyl alcohol or acetone. If you used acetone, it will soften the toner on the silkscreen, so try to avoid the mixture getting on the other side.