Brad,

You've kind of lost me here, because while I know that this thread was
originally started back on 9/24, and has meandered around "topicwise" for a
while, the specific post that I responded to, is copied here for
clarification.

>Interesting, I thought that the copper "balancing act" was only for
>containing possible warpage. Makes sense, though. Thanks for tip.
>
>aj
>
>> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
>>...
>> I did this type of pour and had the board house
>> slap my wrists ...The explanation was that if
>> you have a big pour with lots of copper on one
>> side you need about the same copper on the other
>> side to balance it. Otherwise the acid on one side
>> gets weak while the other side remains strong,
>> resulting in overetching on one side or
>> under-etching on the other

This is when I entered the conversation, earlier today, and this last
paragraph is what I am commenting on.

Specifically, the sentance that begins "Otherwise the acid . . . " is what I
am having trouble with.

I do admit in my initial reply that there are in fact reasons to "balance
copper", but my problem is that I do not believe that this is one of them,
or certainly not a major one.

Please note that the we are simply talking copper removal given the above
parameters, and not talking about different weights (thicknessess) of copper
on different sides of the board, nor are we talking about warpage, but
simply about the last sentance of the above statement (beginning "Otherwise
. . .).

This is why I asked you what you ment by "unbalanced copper", because there
is absolutely nothing in the above statement to indicate different weights
or thicknesses.

Do all of your comments apply when you have different weights or
thicknesses? Of course.

Is designing a board with uneven distributions of copper or uneven
distributions of layers prone to warpage? Of course.

Once again, what do either of these issues have to do with what is discussed
in the above statement that I replied to?

Since I made my comment on the above statement, there have been three
replies that I am aware of, your original reply, a reply by Terry Harris,
and your followup reply which I am responding to here.

Maybe I am not getting all of the emails on this subject, but Terry hardly
constitutes "three others".

I still say that if you limit your term of "unbalanced copper" stricly to
"area", as indicated in the above statement, then I still say that the last
statement beginning "Otherwise . . ." indicates that there is a problem with
the board house, because with proper "agitation" and "circulation" there
will not be a problem that in anyway lives up tp the enormity that you guys
(you and Terry) are making of it. That does not mean  there is no difference
at all, but that just as I said, there is not a "problem", and certainly not
a "major problem".

Do board houses want you to have the minimum amount of copper removal on all
of your boards so that they can extend the life of their etchant? Sure, but
that does not mean that it they have to etch a lot away that it is a bad
design, does it? Of course not.

I would suggest that the only way that this would become a major problem,
would be if there were not enough replenishment of the etchant coupled with
removal of the etchant containing copper in solution.

To me, this problem speaks of there not being enough "replenishment" and
"removal" of the etchant as described above, and if your board house seems
to consider it a major problem, then maybe you should be asking the same
question of "why" as it relates to them. Are they simply dropping your
boards in a tank with out any agitation or circulation too?

Anyway, how does a spray system with a common collector and pump that
supplies the same etchant to all of the spray nozzels, end up with "weak
acid" on "one side" any how?

And please do feel free to pick on me when I need it, which I know I do from
time to time.

JaMi

----- Original Message -----
From: "Brad Velander" <[EMAIL PROTECTED]>
To: "'Protel EDA Forum'" <[EMAIL PROTECTED]>
Sent: Tuesday, October 08, 2002 3:38 PM
Subject: Re: [PEDA] OT - Complex boards and time to Layout?


> Jami,
>
> Unbalanced copper is exactly what the conversation started on,
> uneven distribution of Cu and spaces or gaps across the surface or area of
> the PCB. I am not talking different Cu thicknesses.
>
> I am not trying to pick on you Jami, but I deal with numerous
> fabricators on this very issue day in and day out. To achieve even and
equal
> etching one must have an even distribution of Cu and similar gaps or
spaces
> across a prescribed area. At least three others have answered your
comments
> with similar and like comments, nobody has stood up to defend your
comments.
> Seems like there is a consensus building.
>
> I might add that you may think that your boards are being controlled
> and monitored for undercut but unless you are testing or specifically
> ordering tests (cross-sections) to be performed , then you are probably
not
> getting what you think you are getting.
>
> 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
>

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