[chbot] chemical milling

[Ivo Gorny]

Just to but a different opinion on the table:

I have done a lot of home brew PCBs, and tested a variety of etchants - my
preferred process, using a self-built double sided UV exposure box with
vacuum pump, is:

1) Create the layout and print it on a transparent paper (like architects
use). Laser printer setting on 'Black as possible'.
2) Use a UV sensitive film and expose the layout as a contrast enhancement
to the film. Do twice, if two sided layout.
3) develop like regular B&W film (yeah, that vinegar smell again) - and dry
properly.
4) expose the PCB. Now, I buy photosensitive PCBs, but one can easily buy
the spray with the photoresist and coat your PCB (or copper sheet metal)
yourself. tested that successfully.
5) develop the photoresist.
6) Etch the PCB. I have best results with Ferric Chloride, at ~60°C and
slight movement. I am very careful not to drip or splash around, oh, and
the halflife of the solution can greatly be enhanced by adding a bit of
Hydrochloric Acid when it starts to look more muddy green then yellow. All
other chemicals are too expensive or dangerous and do not offer the
halflife.

The detail level goes down to track/gap widths of 0.4..0.5mm. But with
cheap PCBs available from China nowadays, I am not doing it very often...

The challenge is to get the chemicals for the film nowadays...

If the layout is simple, it can be cut out of plack paper and glued on
clear film, cutting out the step of producing a film.

Ivo

On Mon, 7 Dec 2020 at 13:10, Mark Atherton <markaren1 at xtra.co.nz> wrote:

> In the order of 500u copper. Also wondering if I can chemically-mill
> nickel. Piece is likely to be 20mm dia, with a 750u hole in the centre.
> Final application is a wehnelt cylinder.
>
> -Mark
>
> On 7/12/2020 12:19 PM, ceo at andygardner.com wrote:
> >
> > Copper thickness? (Thinness?)
> >
> > Do you have a rough sketch of what you need?
> >
> >
> >
> > On 7/12/20 12:09 pm, Mark Atherton wrote:
> >> ERT
> >>
> >> On 7/12/2020 12:05 PM, ceo at andygardner.com wrote:
> >>>
> >>> Are you milling a channel in the copper or want to eat right through
> >>> to the other side?
>
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