What are you using this for? If it is to be a current sensor, (just
guessing),  Have you thought of the heat the copper will get under load?
Will it exceed the Tg of the board material in a worst case scenario?

Plating is not a very precise process... and most shops don't have real
tight controls over the thickness which can vary from the morning to the
evening depending on the frequency of plating bath refreshing to nominal
levels and the amount of current applied and time the board spends in
the plating bath. 

 You need to specify what you want on the fab drawing and discuss the
intent with the vendor that makes your boards to get a good result. They
will probably want to charge extra for the service to make sure you get
the copper thickness exact within that tolerance. It's far easier to
place a 1 OHM resistor on the board with it's close tolerance than to
plate the feature into the board. 

The other option that comes to mind is laser trimming of the printed
feature like they do to screened embedded resistors... that might make
it possible to get the tolerance you want by making it a lower value and
then laser trimming it up in resistance to the range desired... but
there is a charge for that as well... 

Interesting... I'm curious about the application and what is driving the
need for it.
 

Bill Brooks | Datron World Communications, Inc.
PCB Designer/Engineer | Office: 760-602-7004| Fax: 760-597-3777 |
[log in to unmask]
1808 Aston Avenue, Suite 230, Carlsbad, CA 92008 | www.dtwc.com

Performance You Require. Value You ExpectTM

-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Steve Roy
Sent: Thursday, October 22, 2009 10:28 AM
To: [log in to unmask]
Subject: [DC] Finished copper thickness...

Hello,

I'm trying to use a copper plane for a small amount (less than 1 ohm) of
resistance and I need to have my 2 oz. finished copper thickness
consistently .0028 inches +/- .0005 inches).  How can I tell if my
copper
weight is consistent across the entire board or plane?  Is there a
specific
IPC standard (besides IPC 4562) that I should call out on my fab drawing
to
hold the board shop to a tight tolerance?

Thanks in advance...

Steven D. Roy, CID
PCB Designer
Audio Authority Corp.
2048 Mercer Road
Lexington, KY  40511-1071
(859) 233-4599 X-159
[log in to unmask]

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