Faster PCB Etching with Ferric Chloride

At times I am very impatient when I am working on a project and want to assemble a working design. If the design is simple enough I will assemble it on a copper perf board, but often the component count is high enough where a PCB is a much better solution. If the design has a really high component count with lots of surface mount components I will send the board out to a fab house only to have to wait a few days to a month for it to return before finally finishing my project. Sometimes this is much too long. What if I want to have a finished design that night? The solution is etching... more specifically fast etching.

I have been etching my own boards with ferric chloride for years with great success. The only downside to this is time. A larger board will take 20 to 30 minutes (sometimes even longer) to etch in the solution. It also requires agitation to keep it etching effectively by keeping the fresh solution contacting the copper. This requires you to either shake the container of ferric chloride or push the board around constantly in the solution as it etches.

My solution was to have something agitate the board for me.



This was my first test of using a VWR vortexer to speed up the process. This device was designed for a lab environment to hold test tubes, beakers, and such. The lower plate rotated around causing a mini vortex within the containers solution that would be placed on it. I have modified it to hold a glass container full of ferric chloride to agitate the solution for me. The glass container I am using is perfect for the job. It is a food container called 'Glass Lock' and has a tight fitting plastic lid that locks into place on all four sides. Nothing will be leaking out of it. I bought two of them for the lids. One has small holes that I drilled to allow fumes to evacuate while the second lid is unmodified to store the solution.

Ferric chloride also works better when it is warm. To facilitate this I mounted a good sized peltier junction to the bottom with an epoxy heatsink compound and supplied it with a 12V 2A power supply. It heats the solution up to about 110 degrees Fahrenheit, still below the maximum ferric chloride recommended temp of 135 degrees.

The VWR vortexer as it arrived has an adjustable speed control, the only issue was it had a minimum speed of 1200rpm. This is much too fast for what I needed. Opening up the unit I found two adjustable resistors that let you adjust the minimum and maximum speeds of the motor. I was able to adjust it all the way down to a nice ~200 rpm, perfect to keep the ferric chloride in motion.

In goes the PCB:



With the lid locked on and the vortexer switched on, I checked the board every five minutes.



Total etching time was about 12 minutes, less than half the time of any previous etching I have done. After a quick sanding here is the finished board before tin plating:



Not perfect, but not bad for less than an hour and a half time. I had the design drawn up in eagle in about 45 minutes, the rest was transferring the design to the copper and etching.

Future improvements will be to add a second peltier device to get the solution up to a higher temperature and to also add a digital temperature gauge to make sure the solution does not get too hot.

555 Contest Entry - Audible Level

The deadline for this 555 contest came up very fast, so here I am wiring my blog post for it's entry right around 2am. Over the past few weeks I have been thinking and thinking, trying to come up with an awesome design that used just tons of 555 timers, but with lack of time this month and after seeing some of the other designs posted around I decided to go for something simple.

The design I am submitting is a level that can be used for any purpose where you need to find a level surface in respect to gravity. Typical levels have a clear tube full of a liquid and an air bubble that you have to visually watch. This design uses two separate audio tones at different frequencies that when a level surface is found, the two tones exactly match producing a single uniform tone. With this design, you can listen for a level surface instead of watching. The video has a brief outline of it's function.

When designing it my first idea was to generate two individual frequencies and mix them together, the results being a sounds similar to DTMF tones you hear on a phone. After testing this I realized that it didn't work as well as I would have liked, it was very difficult to accurately detect the 'true' portion of the level. The resulting design ended up working quite well using two tones that are switched back and forth by a 555 as an oscillator controlling an analog multiplexer to switch the voltages. The second 555 is the actual VCO that generates the tones. When an axis on the accelerometer outputs a voltage that is equal to a reference voltage set, the two tones being generated will exactly match and no difference in frequency is heard. To detect a 45 degree angle, you can take the z axis and either the x or y axis outputs and put them both into the multiplexer instead of the reference voltage.

I left the circuit on a breadboard as I didn't see any rule stating that the design must be a finished product, hopefully that holds true. The 555s are basic NE555 timers that I have had forever. The analog multiplexer is a 508A that came off of some old wire wrapped boards that I believe to be used in old radar hardware. The 508A is a very cool chip, it adds to the vintage of the 555s. The accelerometer is a ADXL-330, 3 axis plus or minus 3G which I happened to have on hand. Another idea originally was to cycle between both x and y axis of it along with the reference voltage in order allowing you to be able to level something in two dimensions. This proved to be more difficult to listen to so I stuck with the single axis idea to measure.

I tested the accuracy of this level to see if it was actually practical to use. I mounted this circuit to a small board and lined it up on a piece of wood. I then 'listened' for 45 degrees and drew a line on the board. Using a regular level and protractor I found that I was at 46 degrees which was pretty close. My accuracy became better in subsequent tests resulting in most of my lines being right at 45 degrees. It is cool to see that this circuit has an actual practical application.

Happy Halloween

We had an extra pumpkin and I had 20 minutes... :)


Happy Halloween.