The following post is more a reminder to myself, how to etch a PCB. I tested a lot and finally found my way to etch all boards, I need for my hobby.
I use Cadsoft Eagle to create the schematics and layout the boards. There is a free version restricted to 2 layers and a defined board-size. For me it’s enough 🙂
As described in thousands of tutorials you can find in the web, I select the Top-layer together with Pads and Vias to print it to a PDF (filled black and mirrored).
Then I switch the Top- with the Bottom-layer and print it to another PDF (filled black but not mirrored).
The both PDF-files I merge in Photoshop to only one PDF with both layers side-by-side with a little distance between. As you can see in the image below, both layers are mirrored to each other, so the raw PCB can be wrapped into it.
The Image is printed two times to an overhead transparency sheet with my old HP Laserjet 2420N. I bought it on eBay for only 9,90€ and with 2400dpi. I’m also able to print PCB with 0.5 pitch elements on it like most of my STM32Fx-MCU.
Next I cut the sheet around the print with a border of maybe 1-2cm around the board and glue it together with superglue, but before the glue I use Acetone in a closed plastic-can for 30 min to darken the toner of both sheets.
Now the glue … I only use small drops of glue around the board and not in the middle between both layers. I use it as double-layer, because the toner is not dark enough for most laser-printers. It uses only a few seconds and I can continue with the process. Why not between the layers? Because next I cut the upper transparency sheet in the middle, so I can fold the lower one along the line between both layers and so, that both layers are congruent with each other.
Now, after pulling-off the protective layer on both sides of the photo-resistive laminate, I put the PCB inside the folded transparency sheet and place this between two glass-panels, I salvaged from old picture-frames. So it’s possible to turn the PCB during the exposure-process.
I use an old Halogen-lamp with a distance of around 20cm for 10 minutes for each side and after that, the PCB can rest for 30 more minutes in a dark place.
NaOH (Natriumhydroxid) is used to develop the PCB. It takes around 2-3 minutes, then you can rinse it under water. It’s no need for destillated water as written in some tutorials.
The next step is the etching process and for that, I use FeCl3 (ferric chloride). I heat it to 50°C on the kitchen stove and then etch the PCB for around 15 minutes.
Be careful, as FeCl3 is dangerous for skin and eyes. Wear protective glasses and gloves. After 10-20 minutes it should be finished and the board can be rinsed under water again.
You can stop here and use the board as it is, but I prefer tinning the board and add a solder mask on both sides. For that I use Sur-Tin and Dynamask.
The final result look like that (it’s another board, a WiFi-shield for my STM32F7-discovery board).