In my electronics class, we made custom circuit boards by drawing with sharpie on copper-clad boards and etching the unprotected sections with Ferric Chloride acid. This process was very time-consuming and yielded large and imprecise boards. To streamline this process, I developed a method of creating PCBs in a similar method using the laser engraver.
This circuit board for a metal-detector uses the whole 1.5"x2" board and leaves a lot to be desisted in terms of accuracy as hand-drawn traces tend to be inaccurate.
My teacher and friends were unsure my idea would work, but I persevered.
These blank PCBs are made from a fiberglass-like material called FR4/G10 or Garolite, which is coated in a 1/1000" thick layer of copper. The process of making a circuit board involves removing most of the copper so that only circuit traces remain.
My first idea was to simply laser-etch away the copper layer but I soon learned that that would not work. The wavelengths of light produced by a CO2 or Diode Laser cutter reflect off copper and do not damage the material in any way. This both made my job harder and paved the way for my next idea.
Since I had to remove the copper using the acid, I would have to protect the areas of copper I wanted to keep with some coating; for this I chose spray-paint as it is cheap, plentiful, and easy to apply.
My first attempt used white spray-paint and only engraved a small outline around the traces I wanted to keep.
The laser lines were from the start a little bit distorted and did not go through the mask layer fully
The next attempt, I used black paint and that seemed to improve the engrave depth but it still only burnt off the pigment and left a thin clear layer that would continue to shield the copper from the acid.
At this point, I am already able to fit the original metal-detector circuit into half the space previously used.
I tested different speeds and powers but none of them were able to go through the clear coating.
After many tests, I tried sanding the board with scotch-brite before dipping it in the acid and that did scrape off the clear layer without damaging the mask. This worked but still took a long time to engrave.
With one pass of the laser, the paint was burning off and leaving residue, to counter this, initially, I had just slowed down the laser but that was wasting significant time so I tried running two passes of the same engrave job which did a much better job.
In parallel with fine-tuning the process, I was also starting to design my own PCBs that could be engraved. I used Fusion 360 eCAD (electronic CAD) to draw out circuit diagrams and design the final PCB.
I used this design to make a PCB with all the knowledge I gained in the previous experiments.
*This video has been significantly sped up; total job was ~10 mins
The Final Process
Step 1: PCB Design
Design a circuit and the corresponding PCB in Fusion 360 using your components.
Step 2: Preparing the Blank PCB
First, clean off the oxidized copper layer with Scotch Brite, then paint over the PCB with matte black spray paint before giving it time to start oxidizing.
Step 3: Engraving
Engrave with two passes, 1200DPI on a laser engraver.
You will have to do some testing to find a speed and power combination that works well, and always prefer higher speed and power over lower speed and power. (some lasers might work better at almost max speed ~95%)
Step 4: Preparing for Acid
Sand off the clear coating to expose the unwanted copper. Then, drill a small hole in an unimportant part of the PCB to tie a string to. Finally, rinse the whole PCB in water and fully dry before putting in acid.
Step 5: Dip Into Acid
Leave in acid with heat and agitator on until all exposed copper has been dissolved.
Step 6: Remove Excess Mask
Use Steel wool to scrape off the excess mask covering the traces.
Step 7: Drill Holes
Use a Rotary Dremel and Dremel workstation/drill press with 0.7mm drill bits to drill holes into each pad.
Final Remarks
Developing this process was a journey that I am grateful I went on as it taught me a lot more than just how to make PCBs with the laser engraver.
Next year, I am going to refine this process to automatically drill the holes and make double-sided PCBs as well.
Resources:
https://www.makerlessons.com/home/circuitree/soldering-and-pcbs - My teacher's website that explains the sharpie etching process in greater detail.
https://www.autodesk.com/education/edu-software/overview?sorting=featured&filters=individual - Fusion 360 free for education
https://www.youtube.com/c/ProductDesignOnline - Very valuable Fusion 360 lessons