pcb etch station

[Adrian Godwin]

The pcb etch station is currently out of use.

The ferric chloride was exhausted and has silted up the bubbler, so it
can't work. I have emptied the tank of etchant and left it soaking
with water as a first stage of cleaning the bubbler.

The cupric chloride in tank 4 has been reported as being exhausted
too. This is recyclable so do not empty it. I cannot test the strength
at the moment as there is no NaOH left - I'll bring some more next
time i visit, which I hope will be Thursday.

If you wish to help, further changes of water in the etch tank and
attempts to clear the bubbler using low-pressure air would be helpful.

Do not connect the bubbler to the big compressor.

Do not put any ferric chloride in the etch tank.


-adrian

[pad...@padski.co.uk]

Great stuff Adrian, I shall do what I can on Monday..
Paddy

Sent from my thing.

[Adrian Godwin]

On Sat, Oct 13, 2012 at 8:29 PM, Adrian Godwin <artg...@gmail.com> wrote:
> The pcb etch station is currently out of use.
>

The etch tank is almost ready for use again.

The cupric chloride etchant in the 4th tank is up to strength and may
be used if you keep the pcb constantly moving by shaking the basket. I
have left the small bubbler running to complete the regeneration but
it's only lightly used. This bubbler should normally be left running
for long periods if the etchant has turned from a bright emerald green
to a denser green.

The bubble bar in the normal etch tank has enough holes cleared to
work, It would be better to clear them all, but they're hard to find.
I understand that the bubble bar is sealed into the plastic tank so I
don't want to disturb that and create a leak.

I haven't yet put etchant into the proper tank, because one of the
failure modes when the pipes block is to blow the plastic pipe off the
rear of the tank, dumping etchant into the floor of the cupboard
(cleaning this up was one of the jobs necessary to sort it out). I
don't want to refill the tank with acid until I've found a good way to
stop this happening.

Please don't refill the tank with ferric chloride.

-adrian

[Russ Garrett]

On 21 October 2012 10:33, Adrian Godwin <artg...@gmail.com> wrote:
> The bubble bar in the normal etch tank has enough holes cleared to
> work, It would be better to clear them all, but they're hard to find.
> I understand that the bubble bar is sealed into the plastic tank so I
> don't want to disturb that and create a leak.

It's been removed several times before (at least once by me), without
causing any problems. IIRC the seal is a rubber compression grommet
thingy which is quite effective.

> I haven't yet put etchant into the proper tank, because one of the
> failure modes when the pipes block is to blow the plastic pipe off the
> rear of the tank, dumping etchant into the floor of the cupboard
> (cleaning this up was one of the jobs necessary to sort it out). I
> don't want to refill the tank with acid until I've found a good way to
> stop this happening.

So, I suspect the way this is meant to happen is that the weakest
joint in that tube is meant to be one of the ones further down the
line (after the tube has been looped above the level of the liquid). I
don't really know how to ensure that, however.

--
Russ Garrett
ru...@garrett.co.uk

[Mike Harrison]

On Sun, 21 Oct 2012 10:54:53 +0100, you wrote:

>On 21 October 2012 10:33, Adrian Godwin <artg...@gmail.com> wrote:
>> The bubble bar in the normal etch tank has enough holes cleared to
>> work, It would be better to clear them all, but they're hard to find.
>> I understand that the bubble bar is sealed into the plastic tank so I
>> don't want to disturb that and create a leak.
>
>It's been removed several times before (at least once by me), without
>causing any problems. IIRC the seal is a rubber compression grommet
>thingy which is quite effective.

The problem is it's compressed by a plastic (nylon?) collar into a plastic (polythene?) thread in
teh tank, and if overtightened, can terminally mangle the thread in the tank.

I've found the long-term solution for these tanks is to ignore the tank bar and use an L-shaped bar
in the basket (This can be the original bar, heat-bent from its normal U into an L), passing up
through the lid, onto which you attatch a silicone tube.
This solves two problems - it's easy to access for cleaning, and if the tube comes off, it's above
the liquid level so no leaks.

>So, I suspect the way this is meant to happen is that the weakest
>joint in that tube is meant to be one of the ones further down the
>line (after the tube has been looped above the level of the liquid). I
>don't really know how to ensure that, however.

Cable tie(s) on the lower joint.
I think the original pump that came with the unit wasn't capable of enough pressure to blow the
tubes off.

[Adrian Godwin]

Thanks for the comments, Russ and Mike - I had thought removing the
pipe was more difficult than that.

No, the original pump failed and I replaced it with a rather more
powerful one, largely because it kept the holes free more easily. It
has flow restrictor but not a pressure control. It does blow the pipe
off more often than it should, and though this is usually the
easily-accessible one on the pump, it has occasionally been the other
one. I could fit a more suitable pump, but this is a very solid,
reliable medical one that's a lot easier to access, and I would like
to keep using it if possible. The pressure is only a problem when the
holes get blocked.

I was intending to at least add cable ties and maybe a pressure
regulator, but I like the idea of the independent bar.

-adrian

[Russ Garrett]

On 21 October 2012 11:16, Adrian Godwin <artg...@gmail.com> wrote:
> I was intending to at least add cable ties and maybe a pressure
> regulator, but I like the idea of the independent bar.

Yes, I think putting a new bar in (and potentially capping off where
the old bar was) is definitely the best way to go. It'll make it much
easier to clean.

--
Russ Garrett
ru...@garrett.co.uk

[Adrian Godwin]

The etch tank has been refilled with cupric chloride etchant. This can
be rejuvenated easily and will not, I hope, suffer from silting up
like the ferric chloride (it doesn't have the hard, insoluble waste
material).

Although the etchant will not stain like ferric chloride, it's still
pretty corrosive. Don't get it on your hands or your clothes.

Especially, DON'T PUT FERRIC CHLORIDE in the etch tank if you think it
needs topping up. This will ruin the etchant and we'll have to make
more, which is quite time-consuming and uses a lot of acid.

There are maintenance instructions on the wiki, but Eugene (mentar)
and I will be trying to actively keep it in good condition so this
should not be necessary. Please consult one of us before changing
anything.


A warning : there is a problem with the thermostat on the etch tank.
It's either set too high or it isn't working. On a brief test last
night, the tank got to 50 degrees and didn't stop heating. DO keep an
eye on it, and DON'T leave it switched on. You probably won't need to
get it up to full temperature - it etched a small board in 3 minutes
at that temperature and should probably be made a bit weaker.

There is a small aeration pipe attached to the lid of the etch tank.
This is needed to aerate and regenerate the etchant. I'm sorry, it's a
bit inconvenient when using the washer - we will make it a priority to
improve this. Please be patient with it.

The distribution of ferric chloride around the tanks suggests people
use it rather carelessly, wasting etchant and polluting the other
tanks. When you use the tanks, make sure that you :

1. Allow the basket to drip back into the tank as you remove it. Don't
move it across the workstation while dripping rapidly.
2. Put the basket (and board) through a wash tank before moving to the
next stage. Always use the wash tank BETWEEN the baths you're
transferring, i.e. to the right of the tank you just used.


-adrian