Homebrew PCBs

On 17/02/14 07:01, Philip Pemberton wrote:
> On 16/02/14 16:41, Sam Rod wrote:
>>
>>
>> Perhaps you only need more room for the foam? Or reduce the liquid
>> content translating into more room for foam. Put another way if your
>> etchant is working.... The foam control is a small easily solved
>> byproduct. :)
>
> The tank is 1.5 litres, filled with 500ml of etchant, leaving 6-8 inches
> of space from the liquid level to the top of the tank. The foam was
> overflowing the tank after about ten minutes.
>
> I really don't think 500ml of etchant should produce that much foam!
>
> Aeration is an aquarium air-bubbler hose ("air curtain"), a little like
> this one: http://www.ebay.co.uk/itm/181124311130
> The difference is, mine has a right-angle connector on the end instead
> of a straight fitting.
>
> I checked the chemistry a few minutes ago -- bath parameters are:
>
>    Acid molarity      1.3 Molar
>    Specific gravity  ~1.225
>
> I left a board etching earlier this afternoon - after half an hour the
> CuCl had taken a fair bit of copper off but seemed to stop etching as it
> got towards the end. I ended up dumping the board in the ferric chloride
> tank to finish it off.

Foaming is usually a sign the liquid viscosity is too high. Long etching times 
are a symptom of that too.

The active ingredient should be diluted 1:1 with water. Add a few percent (like 
half a cup) of hydrochloric acid too. When topping up is need every few months, 
just add more hardware shop hydrochloric acid (it has water in it anyway).

With a setup similar to yours (but working properly), full etch happens in 
12mins at room temperature.

An air-ator that blows thousands of tiny bubbles may cause more of a foaming 
problem than one that blows coarser bubbles. Mine blows coarse ones like this:

<http://www.instructables.com/id/Vertical-Etching-Tank-for-DIY-PCB-etching/>