Re: gEDA-user: PCM making methods - was - Re: alarm clock update

[DJ Delorie <dj@xxxxxxxxxxx>]

> DJ - When you are etching your brass stencils they are almost all
> resist and only tiny apatures.  If you work out the cost of inkjet
> ink and the amount of coverage you need - it may make a $200K laser
> cutter seem like a prudent investment :D

More like $90k.  I've checked.  And you can put a drill/mill head on
it and use it for other aspects of PCB making.  But I don't have $90k
:-P

But I use a laser *printer* not a laser *cutter*.  Printing a page of
mostly-black isn't that expensive.

> The photo paper is quite reasonable in terms of quality and I may
> use it from time to time on single sided baords with 16/16 rules.

I do 8/8 with TT but them I'm using the special paper that releases
easily.

> I am going to stick to photo for the DS 6/6 stuff though.

The limiting factor (for me) for the TT is the quality of the edges.
I haven't tried disableing REt though, it might be "dithering" the
edges for me.

> HCl/H2H2 (and the CuCl I use) do not give as sharp an edge as
> FeCl3. Also I think for your brass masks that HCl may not be the
> best solution.  Check with someone smarter than me, but I think it
> is bad with brass.

The problem with brass is that it's *thick*.  Consider an 8 mil
opening in 5 mil brass - the opening is almost *square* vertically.
The undercutting from the etchant distorts the shape of the hole.
Hence my desire to etch from both sides; on 3 mil brass DS you're only
etching through 1.5 mil, not 5 mil, that's 1/3 the distortion.

Comapre to 1.3 mil for a 1oz copper PCB (or 0.7mil for 1/2oz that I
use), and it's a big difference.


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