Homemade PCB: Part One – My Method
As I mentioned in the last post, the power supply for TLC-MBC will be replaced and I’m going to do this with a homemade PCB. This is another first for me, making a PCB. The post will be in two parts, this part will detail everything from what materials I used to what I did, so let’s get on with it..
There are several ways of making a PCB at home, the most popular are:
Toner Transfer Method: The layout is printed by a Laser printer onto paper which is then placed face down on the copper and heated by either an iron or passed thru a laminator to bond the ink to the copper. It is then soaked in water to remove the paper. This leaves the “ink” on the copper which is used to resist the etchant.
Press and Peel: This is similar, again the Laser is used to print the layout but it is on a blue film. This is then pressed down and heated, by iron or laminator, to fuse the ink. Then the blue backing is peeled off. No soaking required. Still need a source of heat but not as messy.
Photographic Method: The layout is printed on a transparency by either Ink-jet or Laser printer. This is then pressed flat on the coated copper and exposed to UV light to develop the coating.
Ink Resist Pen: For simple PCBs all you need is an Ink Resist Pen. Two disadvantages are that it is easy to get finger prints on the copper and you have to draw the circuit back-to-front.
I haven’t got a Laser printer yet, even so the first method sounds a bit messy to me. The last method – forget it! To me there’s to much room for error. This leaves the Photographic method and this looks doable so that’s the method I chose and will explain here.
Homemade PCB: Method
A lot of links are coming up for products that I used, they are NOT affiliate or tracking links. They are there to show you what I used so you can choose to get the same or not – it’s up to you.
As I have an ink-jet printer, I got some sheets of ink-jet transparency and used Kicad to print the traces. The transparencies have two sides, rub your finger against each side one is smooth the other is not – this is the side you print on then let it dry for a couple of minutes. As you can see, I printed the circuit back to front, this so that I can place the ink side next to the copper and it will be the right way around.
For the Photographic method your copper has to be coated with a photo-sensitive chemical. You can buy it in a spray can and do it yourself or you can get pre-sensitized boards. I chose the pre-sensitized as it is one less thing to wrong as I am learning. The local Maplins store had 100x75mm board for only £1.99, so I snapped up a couple of them. As the PCB is roughly 60x40mm I cut one of the boards to size with a hack saw.
The boards have a protective layer of plastic that must be removed before exposure, this must be done in a darkroom. I attached a couple of red leds and a resistor to a 9v battery so I could see what I was doing. I removed the plastic, placed the printed side down on the copper, careful not to touch the surface, and sandwiched this in a picture frame.
To expose the PCB I got a 40w Spiral 6400k Cool Daylight CFL Light Bulb B22 E27, contrary to belief, you don’t need a UV box. I left it for 15mins to expose while I went and made up the chemicals.
From this point on you should wear some latex gloves and probably eye protection at a bare minimum.
You will need three containers, preferably with air-tight lids. First the photo-resist developer, this removes the exposed bits to leave the traces it can take anything from 15secs to a minute. I use a wooden skewer to jiggle the board around. Once developed, I run the board under cold water to wash of any remains of the developer.
Next up is to etch the board. Ferric Chloride has been a popular agent despite the fact that it will stain anything it touches. Don’t really want that so I chose this etchant. It takes a little longer, but it’s not as messy. I dissolved some crystal in the second container and then placed this container in a larger one of hot water. This kept the temperature of the etchant up so that it would work faster. Again I jiggled the board around with a wooden skewer. It seems to take about five minutes to get started. First the edges go then there’s a speed up and the rest of the copper is removed quite quickly. As soon as it’s done, I pulled it out and run it under cold water to remove any traces of etchant and used a paper towel to pat it dry.
Many would stop there and drill the board. But there are several other treatments that are available. There is a green PCB mask that you can spray on and solder thru – a bit messy for my liking and expensive. There is also a Dry Film Solder Mask that is photo-developed like the traces were. But my favorite is to plate the traces with tin. Not as hard as you might think. Get your third container and dissolve some tin plating crystals in it. Leave the PCB in there for five to ten minutes. Job done, again under the cold water for a rinse.
The homemade PCB is now ready to be drilled. I have a Dremel clone from Maplins and thought I would use it. The smallest drill it will take is 1mm which is a bit large for a PCB, but I’m cheap 😉 so that’s what I used. As you can see, the results aren’t that great, some of the pads are now no-existant.
The last step is the silk screen on the front of the PCB. I found this vid on YouTube, word of warning if you don’t like Benny Hill turn the volume down or off! This method looked very easy so I went and had the silk screen printed for me on a Laser printer and followed the instructions. Unfortunately it didn’t work for me. I do have another way. I have some sticky backed transparencies that the ink-jet can print on. I shall try that, the only disadvantage is that all the holes have to be poked thru as I would apply it after the holes are drilled to get it in the right place.
Thoughts on the Homemade PCB
I stopped at this point, I don’t want to waste any components on this homemade PCB. My first mistake was being cheap and getting the Maplins boards. There were two reviews and they were bad, I should have listened..if you look at the last image, you can clearly see the damaged parts, it looks like something has scratched or pressed into the surface. So I have ordered some fresh boards. Also the “Dremel” was a false economy, so I bit the bullet and have ordered a suitable drill.
The other thing that I will change is the size/shape of some of the pads so that there is more room for error. On the whole making a homemade PCB has been a fun experience, it took about an hour from start to finish and it wasn’t messy. So although I have a naff board, I’m not disappointed as I’ve learnt something and I have plans now for other homemade PCBs in the future.
I have plenty of chemicals left and intend to reuse the already diluted stuff as I have them in sealed containers that are marked with what their contents are on the lids. I just have to wait a few days for the new PCBs and drill to arrive and I will post part two of this.