PCB etching tutorial

In the previous tutorial I wrote about how to draw a schematic and design the PCB layout using eagle, now it’s time to actually use that to etch the PCB.

Things you’ll need:

1. Single sided PCB.
2. Access to a laser printer. (An inkjet will not do)
3. Photo paper. This is the most important part in making the PCB, The kind of paper you use will decide how good the transfer will be.
4. Iron box.
5. Drilling machine which can hold 0.8mm and 1mm drill bits.
6. Ferric chloride powder(Etchant).
7. Nail polish remover.

Other stuff:

1. Scotch Brite.
2. Plastic container slightly bigger than the PCB.
3. Gloves.
4. Safety Glasses.
5. Tooth brush.
6. Plastic(preferred) or metallic forceps.

Theory:

A PCB can be made by many methods like UV etching, Toner transfer method, using a CNC mill etc. We’ll be doing it with the toner transfer method as it’s the only method which doesn’t require access to expensive equipment/materials.

To make a PCB you need two things, an etchant and an etch resist. The etch resist is a material you put on the PCB where you want the copper to stay intact. In the toner transfer method, the toner of the laser printer acts as the resist. The toner is a kind of a polymer mixed with carbon that sticks to the paper when heated.  The toner should be heated until it becomes sticky enough to hold on to the paper but it’s not enough if it’s just heated, a lot of pressure has to be applied to fuse it with the paper. This is what the laser printer does when it prints a paper. What we need is to transfer the toner from the paper to the copper board to act as the resist. To do this, we need to put the paper on the board and heat it using the iron box and apply a lot of pressure. There are people who have modified laser printers to directly print on a copper board but that’s a very complicated method. The kind of paper you use to print the layout can make a huge difference. After a lot of experimentation I found that glossy photo paper work really well, the higher the DPI(dots per inches) the better. You can get a pack of 20-25 papers for around Rs.150 depending on the quality of the paper. After the paper is pressed on to the board and heated, its removed by soaking it in water and rubbing it off. Only the black toner remains on the board after this. Now the etchant comes into picture, the etchant I use is Ferric chloride but you can try a solution of HCL(about 20%) and Hydrogen peroxide(the stuff you get in medical stores) if you can get a hold it. When the board is immersed in the etching solution, the etchant removes the copper wherever there is no resist and the copper remains intact wherever there is resist(that’s why its called a resist). You can now clean the board, drill holes and solder the components.

Ok enough of theory let’s get to the good stuff.

Taking the print out of the layout

If you came here from my previous tutorial about making the schematic then you’ll already have the layout ready in eagle or if you have another layout you can use that.

Open the layout in eagle. If you’re re-opening the file, you might not see the power planes. To see it, go to Tools and press ratsnest.

Now we need to hide all the layers that we don’t need. Go to View>Display/hide layers and select only bottom, pads, vias and dimension.

Your board should look like this

If you don’t own a laser printer and you need to get it printed outside and the guy at the cyber café won’t allow you to install EAGLE, you should export the layout as an image or convert it to PDF. If you export it as an image, the size of the layout might not be to scale when you print it unless you have an image editing software like photoshop. So I suggest you to convert it to a PDF. Go to File>print and tick “Solid” and “Black”. Do not tick “Mirror”. Now press PDF and give it a name, you can use this file to print the layout.

When you’re printing the layout and if you can access the printer settings make the following changes.

Change the type of paper to “Transparency”, this will offer the highest toner density. Turn off any toner saving mode. Choose the highest DPI available and if you have an option to make the print dark, choose the darkest option. It’s better to take the print out when you’re ready to Iron it because you might accidentally touch it or rub it against something and damage the print.

I’ve tried many different kinds of paper like magazine paper, transparent sheets, tracing paper etc but the glossy photo paper always gives me the best result.

This is the brand of the photo paper I use –

If you have a laser printer at home then you can save some photo paper by doing this –

First take the print out of the layout on a normal paper

Next cut a piece of photo paper slightly larger than the layout and stick it to the paper using insulation tape like this

The tape should be near the top of the layout such that it goes into the printer first. You can now put the paper in the printer and take the print out.

Preparing the PCB

Before you can transfer the layout, you must cut and clean the PCB. Use a paper cutter to make deep markings on the PCB and snap it to the required size, leave some room for error.

Uncut PCB

Paper cutter

PCB marked with one of the dimension

PCB after snapping

 

PCB cut to size

 

PCB after filing to make the edges smooth

Cleaning the PCB

Do not use a metallic brush to clean it as it might scratch the surface of the board. I’ve found that  scotch brite does the job excellently(The green stuff which is used to clean utensils). Put some kind of dishwashing liquid if it’s necessary and scrub it with the scotch brite until you can see your face on the copper. I’m just kidding but it should be really clean and shiny like this –

Now dry the PCB using a piece of cloth. Next take a light colored cloth and put some nail polish remover on it and start rubbing the board, you should see some black stuff on the cloth. Move to a clean area in the cloth and put some more nail polish remover and rub it again. Keep doing this until there’s no more black stuff. From now on nothing should touch the PCB except the paper.

Ironing the layout

Before you take the printout, switch on your iron box and turn it up all the way to the maximum setting. Now take the printout on the photo paper and cut it to the exact dimension, do not leave extra space around the edges as it’ll affect the outcome of the PCB when you remove the paper.

Place the layout facing down on the copper side and gently slide the iron box until it covers the whole layout.

Now put a lot of pressure and hold it for at least a minute but make sure you don’t move the paper and also that the paper is flat. After this the paper will get stuck to the board and you can’t move it even if you want to. Now slide the iron box all over the layout and cover every inch of it for a few times.

Now incline the iron box so that only a part of the tip touches the board and rub it all over the board putting pressure. The incline should be really small so that the tip doesn’t accidentally cut the paper.

This step will ensure that all the toner gets transferred correctly. If you do this with a  magazine paper or any other thin paper, the transfer gets smudged and becomes useless. Now iron it again for a few times with the iron flat.

Taking out the paper

After you’ve ironed the layout, let it cool until you can touch it with your bare hands. Now put the board in a soap solution and let it just sit there for at least half an hour.

The soap helps soften the paper so that it can be easily removed. I’ve found that Mr.Muscle(It’s a brand of spray you get to clean stuff) works really well. Leave it for at least 30 minutes. The longer you leave the board in the soap solution, the better, but who’s got the patience really?

Now slowly try to remove the paper, do not force it if it doesn’t come out, try to remove it layer by layer by rubbing in circular motion.

There’s still a layer of paper left. This is toughest part to remove. Try to remove as much as possible by rubbing it with your fingers. Mine came out easily since I’d left it for a few hours.

If the final layer doesn’t come out easily, take a tooth brush and gently rub it in circular motion.

Now dry it with a cloth. If there is any paper left, it’ll become white and you can easily see it.

You can see that there’s a piece of paper stuck between two wires, remove it carefully using a safety pin. Any paper stuck on the board will act as an etch resist, so be sure to remove them. You can also see that all the holes are covered with paper, it is a good idea to remove them too as it’ll help you guide the drill bit easily when drilling.

If there’s a place that the toner is missing or is light, take a permanent marker(Use a Camlin OHP marker, I’ve found other brands don’t work as well) and fill in the missing parts.

Etching

If you’re in Bangalore, you can get a box containing ferric chloride in SP Road which costs about Rs.25. Get a plastic container which isn’t too deep but it should be able to hold the PCB fully. The lid of a plastic box works really well.

Warning : Do all the etching outside as it is extremely dangerous. Do not inhale the gases, they’re toxic. Always wear Gloves and Safety Glasses.

Fill the plastic lid with water, and slowly add the ferric chloride powder. The amount of ferric chloride you add depends on the amount of water you’ve taken. On the container, it says that to make 1 liter of solution you need 500gm of ferric chloride, that ratio seems about right.

Now slowly put the board inside the solution and immerse it completely. Now start rocking the container back and forth to speed up the etching process.

After about 10 minutes, take out the board using the forceps and put it under running water. See how much of the etching is complete and put it back. This’ll give you an estimate for how much longer you’ll have to etch. Etching it for longer than necessary is also not a good idea as even the copper under the resist gets removed. So stop it as soon as its done.

The area inside the red portion hasn’t completely  been etched.

After a couple of minutes take it out again and see how much is complete, if its fully complete move on to the next step, else put it back and rock it till its complete.

Drilling Holes

After you’ve etched the PCB, clean it and dry it. Now its time to drill the holes. To drill the holes you need a drilling machine which can hold really small drill bits. If you’re in Bangalore, you can get this in SP road, it’s called a PCB drilling machine, its really cheap but it’s a hand drill and it takes quite some time to drill. If you want to drill faster, you can invest in a portable drilling machine which will be useful for many other things too. You also need to get 0.8mm and 1mm drill bits which cost about Rs.10 per bit. Get some extra of each as you’ll be breaking a few on your first try.

Soldering the components

Before you can start soldering, you have to remove the toner. Just scrub it with the scotch brite till you can see the copper. Now clean it with the nail polish remover  to remove all the dirt. It’s a good idea to solder it right after you’ve done this, if you leave the board for a long time then the copper will oxidize and make it harder to solder, in which case you have to scrub it again.

Video of etching coming soon.

Please leave your questions/comments below.

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