Home made Printed Circuit Boards (PCBs) are a great way to try out your prototypes before sending them for manufacturing. The toner transfer method is a simple way of making PCBs because all you need is a printer, an iron, some laminate and etching agent. However, if your design requires two layers, your challenge is to align them. If you fail to do so, your vias will not connect the layers properly. You might also run into a situation in which you drill through a pad on one side but end up on a net on the other.
In this instructable I will show you how to make a double-sided PCB at home without any extra equipment. It is my first instructable so feel free to let me know what can be improved. Here we go!
Step 1: Print
To begin with, you need to have your board designed. I use Eagle CAD, but it can be any other PCB design tool. Although this instructable is about two-sided PCBs, I recommend using as few vias as possible as this will limit the amount of work later on. It's recommended to include mounting holes in the corners. Even if you don't need them, they will make aligning the layers easier.
Once you're done, you can print your design on glossy paper. Remember to use maximum toner density and resolution.
For the top layer, print the design as a mirror reflection. Include nets, vias and pads. In Eagle I add the dimension layer to make cutting the board easier.
When you print the bottom part, make sure you do not select the "Mirror" checkbox. Otherwise you'll end up with a print that you'll need to transfer through paper. This may be difficult. For the bottom layer include nets, dimension and vias. It is not necessary to include pads.
Step 2: Prepare the Board
Time to get your hands dirty! We'll start by getting the laminate ready. Cut your print along the dimension layer lines with scissors and use a marker to get the dimension on the laminate. Now you'll need to cut the laminate. You can do it with a small saw or very sharp scissors. Once done, remember to clean the top layer well to remove any dust and grease. I use a kitchen sponge and extraction naphta, but any good solvent will suffice. Wear protective gloves!
Step 3: Transfer the Top Layer
The next step is to transfer the printed design onto the laminate. Start off by carefully aligning the print with the laminate you prepared. Make sure not to touch the laminate as grease from your palms may prevent the toner from transfering properly.
Set your iron to max, do not use steam. Keep pressing the iron for about 5-6 minutes. Move the iron around, especially close to the edges to ensure the toner is fully transferred. Towards the end, you should be able to see the PCB layout through the paper. This means the toner has melted and you're ready to remove the paper.
Let the PCB cool down for about a minute and place it in lukewarm water. It shouldn't be hot, but it should not be cold either. About 40-50 degrees Celsius should be just fine. Leave the board be for a while until you see the paper starts peeling off at the sides. You can now gently remove the paper from the board. If it doesn't come off easily, give it some more time.
Step 4: Align the Bottom Layer
Now that you have the top layer on the laminate, it's time to take care of the bottom layer. Start by drilling holes on your PCB. It is recommended to use mounting holes in the corners of your PCB. Even if you don't need them, it is recommended to include them just for this purpose (thanks to MikB for this tip!). If you don't have mounting holes, use vias. You don't have to drill through all of them yet and in fact it's better if you select only those that are as far apart from each other as possible (e.g. close to corners). You will use them to align your bottom layer with the top one. If you drill through vias, small pieces of toner may come off during drilling. Do not worry about this, just make corrections with a PCB marker if needed.
After the holes are drilled, clean the bottom layer to remove dust and grease. Now take the paper sheet with the bottom layer of your PCB printed on it. Punch holes through vias using pins. Then, push the pins through the holes drilled in the PCB, with the paper sheet still on them. This way you've just aligned both layers of your PCB.
You can't use your iron just yet because pinheads are in the way. I use insulation tape (more temperature resistant than regular tape) to stick the paper to the board. Avoid putting tape over the nets of the top layer. As pointed out by rocketman221, Kapton tape works really well for holding the paper on the board. It doesn't melt and leave sticky residue behind like the electrical tape. Remove the pins once the paper sheet is firmly in place.
Step 5: Transfer the Bottom Layer
Now you can transfer the bottom layer onto the laminate. The procedure is the same as with the top layer. I add an additional sheet of baking paper to ensure the iron doesn't get glued to the tape.
After you remove the paper, clean the glue left over from the tape. I didn't which is why you can see copper residues where the tape was stuck.
If needed, now is the time to make final corrections with PCB marker.
Step 6: Etch!
Time to start etching. I use sodium persulfate. You need approx. 100 grams per 500ml of water. Dissolve the powder in water that's about 50 degrees celsius and etch in about 40-50 degrees.
In order to control the temperature, place a smaller container in a larger bowl. This way you can add a little boiling water to the larger bowl while maintaining stable temperature for etching. It will also ensure that if you need to increase temperature by adding hot water, you do not change the proportions of the sodium persulfate solution.
Stir the liquid when etching as this will speed up the process.
Once no more copper is visible, remove the toner with a sponge. You can use the same solvent as you did for the initial cleaning of the laminate.
Step 7: Solder the Vias
Your vias are not plated so you need to make sure they conduct signals. I use remainders of resistor legs, but you can use any conductive material, such as jumper wires. Solder on both sides of the board and cut the excess.
Step 8: You're Good to Go!
Drill the remaining holes and solder and connect the other components to finish your board.
You're done. Enjoy your new gadget!