Terry please see below

----- Original Message -----
From: "Terry Harris" <[EMAIL PROTECTED]>
To: "Protel EDA Forum" <[EMAIL PROTECTED]>
Sent: Tuesday, October 08, 2002 12:36 PM
Subject: Re: [PEDA] OT - Complex boards and time to Layout?

> On Tue, 8 Oct 2002 11:18:07 -0700, you wrote:
> >Some boardhouses may still "dip" or submerge the board into an "etchant
> >tank", where the board simply sits in the etchant, however, there should
> >enough "agitation" or "circulation" of the etchant to prevent what they
> >describing from happening.
> Nothing you can do will eliminate the problem, just hope to reduce the
> effects. A lot of copper in one area of the PCB will take longer to etch
> resulting in over etching (undercutting) in areas with less copper. The
> board house can't afford to over etch because some tracks will undercut
> unacceptably (or even completely and fall off the board), under etching
> risks leaving shorts in the dense areas. You are giving them process
> control and yield problems seems reasonable they want you to pay extra.

I can accept this as applies to a board with different weights of copper on
each side, but not for the same thickness of copper (specifically not to the
extent that you appear to be stating here), where the only issue is "area",
and there is proper replensihment and removal of etchant.

(Please see my reply to Brad)

> Before the etching problem there is a similar problem with plating. Need
> 100A for the copper on one side of the board and 5A for the other - how do
> you arrange that? I think the only thing they can do is fiddle around with
> anode spacing on each side of the board to try to balance it a bit. They
> can't plate at 100A anyway because it puts too much current through the
> sparse areas and leaves the tracks with an uneven 'frazzled' appearance.

Plating is an issue that IS related to surface area, and NOT what we are
talking about here, although it would be an somewhat applicable comparison
if in fact there was no "agitation" or "circulation" of the etchant, which
is what I was saying was a problem in the first place.

> Again you are giving them process control and yield problems and slowing
> them down.

Again, I will state that I believe that the original statement by the board
house, as stated in the post that I responded to, indicates a problem with
how the board house is dealing with the board (unless there are addional
factors that were not stated, such as uneven weights of copper on the
different sides of the board).


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