I’ve always wanted to learn how to make a nice PCB that I would be proud to show off. Up until now, I’ve always used perfboard and jumper wires to make my (somewhat) permanent circuits. This had worked great for some of my smaller designs which didn’t have a lot of connections but it was still a pain. Like I said, this worked great for my smaller projects but I have a new design I’m working on that is quite big and a floating rats nest of wires just won’t work anymore.
Short of sending design files off to dedicated PCB manufacturing houses, the only other way I knew of to create a PCB was the tried and tested toner transfer method. I’ve heard of many people claim they had great success in this method of PCB etching but I’ve also heard of even more horror stories about it too. Thats when I discovered the photoresist method. Simply put, you print your ‘positive’ layout (the copper material you want to keep) on a transparency. Using this photomask, you expose a pretreated copper clad board to UV light (again, with the mask covering what you want to keep) then develop this board to remove the resist that you don’t want. The rest is the same as every other method – etch, clean, enjoy.
I won’t go into too many details here simply because there are so many other great tutorials online to follow. I will just go over my experience and how the results turned out.
First, I needed a PCB layout to actually print to act as a mask. There are a lot of great tools out there but in the end I chose DipTrace. Everywhere you go you hear Eagle this, Eagle that so I gave it a try and hated every minute of it. There is a huge learning curve involved and I simply didn’t like the program. Thats when I discovered DipTrace. Its incredibly easy to learn and has a massive library of components. What they don’t include in the library can easily be created in their component editor. This may seem like a shameless plug but I really like how easy it was for a beginner to use. It also doesn’t limit your board size like Eagle does for the free version. Granted, your limited to just 300 pads in the free version, but anything I create at this stage will surely be under 300 pads.
I got started with my schematic first, adding components then connecting everything up and rearranging it to look nice. “That was easy,” I was thinking to myself – well I was wrong but more on that later. I then exported it to PCB and drew up my board. I knew my board was 5″ x 3″ so I drew the board and began adding components. After locking them into place, I told the editor to auto-place the components (big mistake). It sat there trying to find the best way to situate everything and after a while, it was sure it found the best configuration. “Great,” I said. I then set the auto-router to single sided board (as this is my first board, I don’t want to start running with two sided boards yet). I then clicked auto-route and sat back, waiting for the perfect board to appear before my eyes. Boy was I mistaken. After a short minute it said it routed what it could and left me with a jumbled mess of nets that have yet to be routed. Let me just take a step back here. As a beginner starting out with single sided boards, you are going to have to route your own lines.
I learned this the hard way as it refused to autoroute anymore than half of my circuit. It was a little touch-and-go at first while trying to figure out the best way to route the board. In the end, I had to go back to the schematic many times to change component connections in an attempt to optimize routing. I was left with a handful of lines that just wouldn’t route. Thats when I discovered jumpers. It was very simple to place a jumper – so simple in fact that I’m sure I overused it. But in the end, I wound up with a good design.
So onto the next step, printing it. I used some transparencies I bought at the store to print to (using a laser printer of course). I removed all the layers except what I wanted to have on copper then printed. After several failed prints (jams, smudges, etc) I ended up with one that looked good. I then cut it down to size and retreated to my lair-um-garage.
While in the garage under the assistance of a 8 watt nightlight, I carefully removed the board from the plastic bag it had been in since 2011. I pealed back the protective film to expose the green photoresist. I carefully lined up the board with the transparency making sure the image was reversed. Once I was happy with it, I placed a piece of glass I stole from a picture frame on top and set my UV light on top. Now many people online discuss their light sources. Some use the sun, some build crazy contraptions, others use desk lamps. The directions say to use a ‘daylight’ fluorescent bulb (26 watt I think) however I went ahead and bought a UV light box a while back for curing UV sensitive paints.
This same device is sold on everyone’s favorite auction site to cure nail polish. Without knowing how long to expose the board I went ahead and used the 120 second timer built into the UV light and switched it on. After a painful 2 minutes, I anxiously removed the board from the setup and lowered it into the developer. First nothing happened and my heart sunk. Then I brushed it slightly with a foam brush and the bare copper was beginning to peak through. I continued to brush it until I could see the design and I immediately moved it to my second tray to rinse it off.
There I have it, my board with the unneeded resist washed off, ready to be etched.
Now there are many different tutorials online that describe many different ways to etch the board but most of them boil down to two different etchants: Ferric Chloride or Hydrochloric Acid with Hydrogen Peroxide. I’ve used Ferric Chloride many many years ago when I was playing around with a kit I got. I remember it being nasty and stained anything it came in contact with.
For this reason I decided to go with the Hydrochloric acid and Hydrogen Peroxide. Again, many good tutorials out there for how to mix it and use it. I was very impressed by how fast his solution etched away the copper. I believe it took less than 8 minutes overall but then again I wasn’t timing it. After all the unwanted copper was removed, I rinsed it with water and admired my new board.
After the board was rinsed clean, I removed all traces of the resist using some acetone. I found some nail polish remover at the grocery store that was labeled professional strength. This basically means that its 100% acetone and not the watered down and nice smelling stuff ladies use on their nails. I wiped the board several times with a fresh paper towel to remove all traces of the resist.
Now I could have stopped there and drilled the holes but I decided to take it one step further and throw on a solder mask. This would really make it look professional! I found this material (again on our favorite auction site) which is applied very similar to the photoresist process. The solder mask is photosensitive so the entire process is done under my tiny nightlight. The material is applied to the PCB and fed through a laminator several times to ensure it bonds smoothly. A second transparency is printed but this time with just the solder pads. The board and transparency is aligned the same way and held in place with the help of some glass.
The board is then exposed for just one minute and then the pads are washed off with a mild solution of sodium carbonate and water. This leaves just the pads exposed and the rest of the board covered in the solder mask. It is then placed back under the UV light for 30 minutes to finish curing the mask. Afterwards, I have a nice solder mask.
The next, and probably the funnest part, is drilling all those holes. Luckily I have a dremel drillpress but it still was less than fun. I found that my dremel shaft has a lot of wobble to it. luckily the holes in the pads allowed the bit to self center itself which made the process easier. I did run into a bad problem with the drill bit broke and ate up part of the board. Luckily for me it was around the groundplane and no traces were damaged.
Last, all the components get soldered on and the board is finished! The soldermask definitely helped during this stage.