On 5/1/08, warrenbrayshaw <
warrenbrayshaw@...> wrote:
> I have been pondering the false walls idea for a while. I would
> experiment with driving the bubbles up the tank walls to cause the
> return flow of 'Unbubbled' etchant to flow down the surface of the
> PCB. -This should take away the etching issues caused by the
> incorrect bubble size or rate of bubbling.
>
> The spacing between the false walls and the PCB should be kept small
> to ensure there is a decending flow at the surface of the PCB. As the
> etching by-product is heavier, having a decending flow makes sense.
>
> The bubble bar/hose should be a little way up in the bubble channel.
> I suspect the greater the column height of the bubbles the greater
> the etchant flow rate will be. Bubbling may need to be much stronger
> with this arrangement to induce the desired flow
The false walls mustn't be too close to the PCB either or the flow
will be impeded. I don't think "bubble drive" will create much
pressure.
I was thinking to have the false walls guide the bubbles towards the
PCB (narrowing at the top), but that would still leave the issue with
distributing bubbles evenly over the length of the PCB. This idea
would mostly eliminate that problem.
ST
> It would be good if the etch by-products could stagnate on the bottom
> of the tank and not be involved in a new etch cycle. This would
> probably be achieved by having the false walls rest on the bottom of
> the tank but have slots or a row of holes 15cm up the walls for the
> etchant to flow back into the bubble channels during etching.
>
> If the false walls are thick, then less etchant is required in the
> tank.
>
> The etchant decent rate over the PCB surface could be tested with
> water and food colouring.
>
> Regards
>
>