Brad see below . . .

----- Original Message -----
From: "Brad Velander" <[EMAIL PROTECTED]>
To: "'Protel EDA Forum'" <[EMAIL PROTECTED]>
Sent: Tuesday, October 08, 2002 12:25 PM
Subject: Re: [PEDA] OT - Complex boards and time to Layout?


> 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.

what are you saying and meaning when you speak of "unbalanced copper".

first - to my knowledge we are not talking about 1/2 oz on one side and 1 oz
on the other side, which is does in fact cause uneven etching problems, but
that was not stated in the original post that I responded to, nd as far as I
know this is not the topic of this discussion.

secondly - we are not talking about the "warpage" issue which I specifically
excluded.

all that taken into consideration, given the proper circulation of the
etchant (which includes removal of the etched copper now in solution),
copper is copper, and etchant is etchant, and a specific etchant will remove
a specific thickness of copper in a given period of time, irrespective of
whether we are talking about a 1/4 sqiare inch area or a 10 square inch
area.

? ? ?

> 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.

all other things considered, this is usually a "thickness" issue, and not an
"area" issue, unless you are talking about larve "variances" in thichness",
which I would call a process control or material problem.

> The more copper to remove, the more time required. Less copper to remove,
> less time.

again "thickness', not "area".

> 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.

as far as I know this only applies to boards or panels or layer pairs where
the copper weights are "unbalanced" from one side to another, and NOT to a
board or a panel or a layer pair where the weights are "balanced", but there
is more copper to remove on one side or the other.

> 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.
>

again, I / we are NOT talking about different weights of copper on the
different sides, which leaves us with a simple "area" problem, and I don't
think that what you are saying is really applicable, given a proper rate of
etchant replenishment and removal.

> 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.
>

All of what you say above is true for any board in a general sense, except I
can not accept your trying to to apply it to different size areas of copper
where the thickness is the same, because it simply does not apply in
anything more than the most minor sense.

All of what you say does apply where you are etching a board / panel / layer
pair with different weights of copper on each side, but that is not what the
discussion was about.

JaMi

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* To post a message: mailto:[EMAIL PROTECTED]
*
* To leave this list visit:
* http://www.techservinc.com/protelusers/leave.html
*
* Contact the list manager:
* mailto:[EMAIL PROTECTED]
*
* Forum Guidelines Rules:
* http://www.techservinc.com/protelusers/forumrules.html
*
* Browse or Search previous postings:
* http://www.mail-archive.com/proteledaforum@techservinc.com
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

Reply via email to