Jami,
        that's just blatantly not true! There is nothing questionable about
a board house that directs you to issues of uneven etching or plating
because of varying Cu distribution. Not even with spray etchers.

        Spray etchers are generally better than tanks but they are not
perfect either when it comes to unbalanced copper. Some of the best fab
houses using spray etchers will still point out unbalanced etching because
of unbalanced copper, even though they 'can' adjust the spray rates and
pressures to compensate at least side/side or one general area to another.
However, they cannot compensate for variances in a different areas over the
same side. It is all a time issue, how long is the area of copper in the
etchant, spray or otherwise, verses how much copper there is to etch off.
The more copper to remove, the more time required. Less copper to remove,
less time. Thus with unbalanced copper the shop has to define some median
time to adequately remove all the copper to be etched without removing or
undercutting other areas too badly. Remember that these spray etchers are
conveyorized, they can't sense areas of a board and speed up or slow down
the conveyor. Let alone sense what is on the other side of the panel, what
is on the other board within the panel but 16 inches away under the other
etchant nozzles. Or how about the etch nozzles that swivel/sway back and
forth, how would you vary them for differing areas of the board when they
are sweeping large areas of a panel that is also moving. It is all a game of
averages, you average your Cu distribution, they average their etching, you
receive a good well-etched board.

        We tightly control our etching tolerances and undercut on almost all
of our boards. So we go through this all  the time with big high tech
fabricators and smaller low tech fabricators as well. Some of the biggest
etching F-ups and the whining afterward, have come from big high tech shops
with very good reputations and the best etching equipment around. I have had
fabricators hedge their bets against being able to control their etching to
our requirements, until they can see our boards/panels. They are looking for
the even distribution of the Cu in order to meet the tight etching
tolerances.

Sincerely,
Brad Velander.

Lead PCB Designer
Norsat International Inc.
Microwave Products
Tel   (604) 292-9089 (direct line)
Fax  (604) 292-9010
email: [EMAIL PROTECTED]
http://www.norsat.com
Norsat's Microwave Products Division has now achieved ISO 9001:2000
certification 



> -----Original Message-----
> From: JaMi Smith [mailto:[EMAIL PROTECTED]]
> Sent: Tuesday, October 08, 2002 11:18 AM
> To: Protel EDA Forum
> Cc: JaMi Smith
> Subject: Re: [PEDA] OT - Complex boards and time to Layout?
> 
> 
> Rob,
> 
> As AJ points out, part of what they say is correct, and you do need to
> "balance" the layers, and the primary reason is to prevent 
> "warpage" and
> related problems.
> 
> However, the remaining issue, is raising a "flag" about your 
> boardhouse.
> 
> Most boardhouses today use equipment that continually 
> "sprays" the etchant
> on the surface of the board, and hence also washes away the 
> "etched copper".
> 
> Some boardhouses may still "dip" or submerge the board into 
> an "etchant
> tank", where the board simply sits in the etchant, however, 
> there should be
> enough "agitation" or "circulation" of the etchant to prevent 
> what they are
> describing from happening.
> 
> What they are telling you is that they simply "dip" your board into an
> etchant tank and leave it there, with no "agitation" or "circulation",
> which, yes, will cause the symptoms they describe.
> 
> But they are also telling you that they are not making your 
> boards properly
> and that you should be looking for another boardhouse.
> 
> JaMi
> 

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