Glass Printed Circuit Board- Part 1

One day I stumbled upon this post from my favorite website. The YouTuber laid out her process for building printed PCBs on glass. The idea struck me, and I decided I had to pursue this idea, and see what I could come up with. And the best idea I could come up with is a binary clock. Clocks have always been interesting to me, it's my dream to build a mechanical clock movement some day. For this particular project, my ultimate goals it to implement the clock using nothing but counters, and logic gates. I have the schematic designed out, but because of the sheer number of components involved, I have decided to start simpler, and power the clock from a micro controller. 


I will continue to update this with my progress as I go along.

EasyEDA is an invaluable tool that I discovered for the first time from the video linked above. It does a surprisingly good job helping you to build a PCB layout. It took a minute to get the hang of the software, but once I did it's amazing how easy it is to design and tweak a PCB with the correct specs.

To start off, Since I currently own a Cricut Explore Air, I decided to follow the same process as the Youtuber. I bought the adhesive backed copper foil, designed then exported an SVG from EasyEda, and got to cutting. After some soldering, here is the final result:

I cannot tell you how difficult it really was to get a successful cut from the Cricut. I cut and recut, and redesigned, and tweaked cutting parameters over and over again, I honed the blade, and even switch to using deep cut blade. But without fail, some of the smaller copper traces would become dislodged during the cut, or if my parameters were such that it would not dislodge any pieces, half the pattern would be merely embossed in the copper because the blade did not fully puncture the foil. Using a deep cut blade, and making the traces thicker seemed to do the trick, though I half suspect I got lucky on the last one as I still had to use tweezers to align some traces . I believe the copper was not stuck strongly enough to the backing for the cricut to cut at that detail. I decided the level of detail I was able to achieve is not going to work for some of my more complicated designs. I would have loved for it to work, but after so many tries, I had to  abandon the Cricut process for the time being.

A note on how I soldered those SMD components; I bought simple solder paste, and squirted the tiniest bit onto each copper pad. I then put the LEDs into place with some fine tweezers (The solder paste is a little sticky, so they stayed), and heated it up in a skillet on my stove. I started heating slowly. When the solder paste started to melt, and flood every where, as this was my first time ever doing any kind of SMD/Reflow soldering. I got nervous that this wasn't going to work out. I may have used a bit too much solder paste too, but I kept the faith and pushed through. I made sure the board was properly heated through, then I turned up the heat. What started to happen is the dull grey solder paste turned into a shiny liquid metal (Just like you're used to in traditional soldering!), and all the flooded solder retracted back onto the hot copper traces/LED leads. I was so happy, especially so when I tested it and discovered that there wasn't a single bridge or NC lead. That leads me to believe that SMD soldering is very forgiving, and you don't have to be an expert to get the solder where you want it.

With the PCB from the cricuit behind me. I looked to the next technique, acid etching. Etching is the much more traditional and professional way PCBs are made. It involves UV lights, UV sensitive dry film resists, and caustic etching chemicals like ferric chloride. I happened to have some ferric chloride sitting in my garage from when I needed to etch my Damascus steel. I won't really go over the specifics of the process because there are plenty of youtube videos that show how to etch PCBs at home using this technique.

One interesting idea that I haven't had the chance to try yet, is using the cricut to cut stencils for the photoresist. Currently I print out a negative of my PCB onto transparencies. It's not very convenient as I have to carefully stack 3 copies so that it will block enough light. The cricut had a hard time with the smaller details, but that's because it was trying to cut the positive versions, I have high hopes that cutting a negative will work much better. Being able to use a single negative is far more convenient, and improves the quality of the exposed resist, which improves the quality of the final board.

When I update again, I will explain the challenge that I've run into attaching the copper foil to the glass.  Until then here are a couple pictures I took of the first etched board :)