EtchingBox

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The Idea

Build a portable / mobile PCB etching workstation that fulfills these criteria

  • waterproof
  • able to etch 100x160mm double sided boards with 8mil precision
  • low cost. total bill of materials should not exceed 150 CHF
  • diy approach, mostly laser cut plexi and easily sourceable materials
  • fits in a RAKO Box

Some guiding ideas

  • use very little but always fresh chemicals
  • good heat management: etching has to be done at 45-50 degrees celsius, developer has to be kept at >20 degrees as well (in my workshop, temperatures can easily drop below 16 degrees and developing is a pain).
  • all material and chemicals travel in the box. liquid waste can travel in the box as well until it can properly disposed of.
  • should be easy to clean. no electronics exposed to moisture.
  • as few as possible switches and electrical contacts exposed to the harsh etching environment
  • self illuminating

The Project

Components

Power Supply

should be able to provide at least 2 x 2 Amps for heating, 1 Amp for lights and a bit more for micro controller, displays and stuff so at least 12V / 6-8 A, 72W - 100W

still have to find a good / cheap one

Master Controller

Gnusbuino based?

Controls

  • exposure start switch
  • relais/FET for UV lamps
  • 3 letter seven segment display for display of remaining exposure time
  • 2 letter seven segment display: developer temperature
  • 2 letter seven segment display: etching solution temperature
  • 2 temperature sensors
  • 2 FET for heating control

14 pins for display, 2 AD, 4 digital -> Total 20 I/O pins

UV Exposure unit

Slot loading, double-sided UV exposure: put PCB and overhead slide between two glass plates. The mechanism presses glass plates together. Exposure starts when assembly is fully inserted. You can stop exposure anytime by retracting the assembly. Otherwise it will stop at a predefines time interval.

First tryouts with UV fluorescent lamps seemed promising - you can get DULUX S style UV lamps for nail polish hardening on ebay for about 2.50 Euro. But two bulbs, 8cm apart, 6cm distance from PCB don't give an even enough light to expose a full 160x100mm PCB - 3 minutes exposure seems to overexpose the center while the corners still don't get enough light. You can put 2 Dulux S on one ballast, so adding a third lamp per side means 3 ballasts if I want to stick with double sided exposure.

UV LEDs?

LEDs would be much easier to control, they are low voltage DC, safer to operate in a potentially humid environment. You could put plenty of leds dispersed on a eurocard size PCB and achieve a much more even lighting. Just found and ordered these suckers:

http://ch.mouser.com/ProductDetail/Vishay-Semiconductors/VLMU3100-GS08/?qs=sGAEpiMZZMurHQmwyojo5KE6XmIXmZykD37eu9T8%252bzE%3d

Heating

Developing and etching solution have to be heated / kept at specific temperatures. How to build a acid resistant heating element that can be immerse in fluid?

Resistance Wire?

Some ideas: Kanthal/resistance wire in Teflon tubes?

DIY resistance boards?

Or diy etched heating pcbs. Using this chart http://www.mikrocontroller.net/articles/Leiterbahnbreite I easily designed a small pcb with a meander that is exactly 6 Ohms -> @ 12V this means 2 Amps heating. Just how to protect the board from the etching acid? Dumped in silicone, waiting for it to settle - will post back.

Induction?

some smaller scale version of this, with a stainless steel / titanium plate inside the acid bath? http://www.rmcybernetics.com/projects/DIY_Devices/diy-induction-heater.htm

Chemical Containers

Use conventional Tupperware style containers for baths.

Recycling Station / Waste manangment

Developer: NaOH 1%

In DIY quantities you can pour it down the drain without bad conscience.

In this thread: http://www.mikrocontroller.net/topic/139625#1284004 some guy asked Bungard if the photo resist is biodegradable, this is the internet, need more sources, but here's the alleged response:

"Es ist aus umweltechnischer Sicht nicht erforderlich, den Entwickler
überhaupt zu neutralisieren, wenn Sie an ein Klärwerk angeschlossen
sind !

Eine Neutralisierung mit HCL ist aber, wie von Ihnen beschrieben, 
möglich.

Das im Entwickler in Spuren gelöste Harz ist organisch abbaubar und
stellt nach heutiger Sicht keine relevante Gefährdung für die Umwelt dar."

Etching solution: NaPS 20% & Cu2+ Ions

DO NOT POUR DOWN THE DRAIN - the dissolved copper is very toxic for fish and for bacteria doing important work in your water treatment plant.

http://www.tuf-ev.de/workshop/aetzen/EntsorgungAetzen.htm

12.05.2014 Punkt 2: Aetzbad auf PH 3 einstellen. Laut Indikatorpapier ist ph meiner verbrauchten Aetzlösung zwischen 1-2. Ich muss 2 Liter Wasser zu 1dl Lösung geben um auf PH 3 zu kommen. Resultierende Lösung scheint nicht mehr mit Stahlwolle zu reagieren...

Todo

  • find a catchy name for the thing
  • build one for proof
  • spread over the world

Source Files on Github

https://github.com/mirdej/etchingbox