PCB Etching
Contents
Description
A logical extension to the Kicad workshop (electronics design) is to realize the designed PCB. There are 3 ways to produce PCBs at FIXME (with the required components):
- PCB Milling with a CNC Router
- PCB Etching using toner transfer method
- PCB Etching using the photosensitive positive method
Goal
- Make custom PCBs for FIXME members and projects.
Obstacles
PCB Milling with a CNC Router:
- Cost
- Make a lot of dust
PCB Etching using toner transfer method:
- Use chemicals requiring precautions for use
PCB Etching using the photosensitive positive method:
- Use chemicals requiring precautions for use
- Need an insolation box
- Number of step for the process
Components
- Iron(III) chloride / Perchlorure de fer Corrosive!
or
- HCl + H2O2 / Acide chlorydrique + Peroxyde d'Hydrogène (eau oxygénée) => HCl+H2O2 method on Hackaday
Photoresist PCB Etching
Parts
- Uv light (UV LED strip or DIY UV LED fixture?)
- Pre-coated photoresist positive pcb
- Lye (NaOH)
- Ammonium persulfate
PCB Layout
The pcb layout should be the positive (black parts are where copper will stay) and *mirrored* image, full size (1:1) of the layout.
This layout is printed on standard paper with a laser printer (or copier) and set the toner density to the maximum value. This will make the black part really dark so the light can not pass trough.
The paper is then drenched in a 'drying' oil (like sunflower seed oil). This will make the white parts of the paper transparent. Remove the extra oil carefully.
Exposition
Remove the plastic protection on the PCB. Place the printed side of the layout against the copper side of the PCB. Remove the air bubbles captured under the greased paper
Place the PCB & Layout inside the exposure box. Then let the UV light do the work for 3-4 minutes This is a completely arbitrary timing, we should test different values
Remove the PCB & Layout from the exposure box
Remove the the layout paper (if you want to reuse it, you can dry it)
Development
We use a 1% Lye (Sodium Hydroxide = NaOH) solution for development. (Add 10 grams of Lye to a liter of water)
To know if the development process is finished, take a look to the traces. They should be clearly distinguishable.
Etching
The etching solution is a 200g/L ammonium persulfate mix.
The etching process can take to over an hour. To speed up this shit, you can add heat and/or bubbles to the solution.
The solution should take a blue to deep blue hue.
The reaction is (NH_4)_2 S_ 2 O_8 -> CuSO4 + (NH4)_2 SO. The resultant liquid is less harmful than ferric chloride but should still be treated with other chemical waste
Safety
Equipment:
- Gloves
- Goggles
- Lab coat
Docs:
- Iron(III) chloride / Perchlorure de fer : (de) Sicherheitsdatenblatt (fr) Fiche de sécurité
- Stop using Ferric Chloride etchant : [On instructables]
