They may be using the track resistance as a low cost current sensing
element, in which case, ensuring that it meets intended tolerances only
makes sense.

A large fall-out tells the designers that they've got a problem that may
need attention - especially if it does have cost implications. Let them know
it.

Rob Legg
[log in to unmask]

----- Original Message -----
From: "Don Vischulis" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, April 12, 2002 11:48 AM
Subject: [TN] Interesting question


> Techies:
>
> I received the following email today, and it aroused my curiosity.  What
> reasons exist for specifying dc track resistance when minimum resistance
is
> governed by a combination of copper weight and design width, and track
> length?  Is this a case of over zealous specification or is there a
purpose
> behind adding another test requirement to a product with extensive
> specifications?
>
> Don Vischulis
>
> Original message:
> You may be able to help me, as I would
> like to know why - in addition to specifying
> impedance - an increasing number of PCB designers
> and PCB fabricators are also specifying DC resistance
> of PCB tracks?
>
> I have had an increasing number of clients ask
> me about series resistance being specified on
> PCB tracks, but no one seems to know why..
>
> If you are able to help with some of the reasons
> why, I would very much appreciate hearing from you.
>
>
> Kind regards
> Martyn Gaudion
> www.polarinstruments.com
>
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