====== pcb-pool etch bath ======
{{tag>project hardware electronics pcb chemistry howto}}

[[http://shackspace.de/gallery/index.php/Projekte/pcb-pool-equipment/etchbath/DSC_4206|{{http://shackspace.de/gallery/var/thumbs/Projekte/pcb-pool-equipment/etchbath/DSC_4206.jpg}}]]

  * Flower vase
  * 50W aquarium heater
  * Aquarium air bubble thingy with pump
  * 3D-printed top and PCB holder

Note: the PCB holder doesn't have much grip.  The 3D-printed screws are also a bit difficult to tighten/loosen.
 

====== Modifications ======
===== PCB Holder =====
The PCB holder already has some grooves to better hold the board. However, these weren't wide and deep enough to really hold on to the board so we've simply used a saw and widened them a bit.

===== Heating-element =====
The heater is a simple aquarium heater.  By design the peak temperature is 37C controlled by a bimetal switch.
This temperature is not high enough for [[https://secure.wikimedia.org/wikipedia/en/wiki/Sodium_persulfate|sodium persulfate]] (Natriumpersulfat) etching.

The mod overrides the bimetal switch and puts the heating element into an always-on mode.
A temperature sensor element was also fitted inside the heater just above the heating element to measure the approximate temperature of the heating element.  There's a [[http://shackspace.de/gallery/index.php/Projekte/pcb-pool-equipment/etchbath/10k3950|conversion table for sensor resistance to temperature]].

Tests showed that controlling the temperature is not necessary, since the heating element peaks at around 55C and begins to slowly (read: several minutes) oscillate between around 45C and 55C.
The modified heater was able to raise the temperature of the etch batch to around 47C which is a nominal increase of around 10 Kelvin over the unmodified off-the-shelf model.

[[http://shackspace.de/gallery/index.php/Projekte/pcb-pool-equipment/etchbath/DSC_4199|{{http://shackspace.de/gallery/var/thumbs/Projekte/pcb-pool-equipment/etchbath/DSC_4197.jpg}}]] Soldering in the bimetal override.

[[http://shackspace.de/gallery/index.php/Projekte/pcb-pool-equipment/etchbath/DSC_4199|{{http://shackspace.de/gallery/var/thumbs/Projekte/pcb-pool-equipment/etchbath/DSC_4199.jpg}}]] Fitting a temperature sensor inside the heater.

[[http://shackspace.de/gallery/index.php/Projekte/pcb-pool-equipment/etchbath/DSC_4200|{{http://shackspace.de/gallery/var/thumbs/Projekte/pcb-pool-equipment/etchbath/DSC_4200.jpg}}]] Fixating the sensor using hot glue.

[[http://shackspace.de/gallery/index.php/Projekte/pcb-pool-equipment/etchbath/DSC_4201|{{http://shackspace.de/gallery/var/thumbs/Projekte/pcb-pool-equipment/etchbath/DSC_4201.jpg}}]] No more temperature dial, just the cables for override and temperature sensor. 

[[http://shackspace.de/gallery/index.php/Projekte/pcb-pool-equipment/etchbath/DSC_4202|{{http://shackspace.de/gallery/var/thumbs/Projekte/pcb-pool-equipment/etchbath/DSC_4202.jpg}}]] Test-driving the modified heater.