Layout and etching of PCB

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 🙂
eagle_schematic
eagle_board

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).
Layer_top
Then I switch the Top- with the Bottom-layer and print it to another PDF (filled black but not mirrored).
layer_bottom
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.
2-Layer
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.
IMG_0016
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.
IMG_0024
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.
IMG_0019
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.
IMG_0022
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).
IMG_0013

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