We have cuprous chloride vertical rotary etcher.  No evidence of this
phenomenon.

Wayne Thayer

>>> [log in to unmask] 11/22/2006 12:49:24 am >>>
Dan,
As far as I remember someone made in the past vertical etchers.
Interesting, if really PCB etched in such etchers are suffering more
of
"acid" traps.
Edward

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dan Skweres
Sent: Tuesday, November 21, 2006 9:58 PM
To: [log in to unmask]
Subject: Re: [TN] Acid Traps

Wayne,
I have to agree whole heartedly. We use with both cupric chloride and
ammoniacal etchants and never encounter "acid traps" or the likes. I
suppose if I were able to pull a panel off the conveyor of the etcher
prior to rinsing and leaned it against something vertically (not that
I
would) that any traces or features that could trap the chemical would
be
a trap.;)
Dan S

>>> [log in to unmask] 11/21/06 12:34PM >>>
Several weeks ago I challenged TechNetters to get a photo of "acid
trap"
phenomenon.  No one volunteered.  Not a big sample set, but I believe
that this is one of those things which was a problem at the dawn of
pcb
manufacture, but is inapplicable to today's processes.

The closest respondents could come up with was  to point out that
alkaline ammoniacal etch solution has a tendency to eat more copper
once
it has some copper in solution.  But, obviously, this process will
starve itself out too:  There must be a peak copper concentration in
the
bath for highest activity, otherwise the reaction would continue until
the solution was 100% copper decomposition products.

I can provide photos of the inverse phenomenon, which most pcb
manufacturers are aware of:  Pads spaced way out in the middle of
dielectric tend to become over-etched, whereas tight lines/spaces tend
to be under-etched.  No big surprise there, since its harder to get
aggressive fluid activity in tight areas.  For cupric chloride
etchant,
These lone pads really take a beating because once the dielectric
around
them clears, the hungry acid droplets will splash sideways along the
dielectric until they bump into something.

As to boards continuing to etch long after they've come out of the
etching machine, I think that's completely ridiculous.

Wayne Thayer

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