Something seems to be wrong, here. Those numbers seem way too high . . .
I'm guessing that there some uncompensated lead resistances or contact
resistance showing up. I calculate that a 1 inch long 1 mil wide trace of
1/2 oz. copper gives about 1 ohm. If you want some easy suggestions as to
how to get better numbers, I'm sure we can come up with a lot of low-cost
approaches.
Later,
Carl
Carl Van Wormer
Cipher Systems
1800 NW 169th Place, Suite B-100
Beaverton, OR 97006
Phone (503)-617-7447 Fax (503)-617-6550
-----Original Message-----
From: DUTTON Phil [mailto:[log in to unmask]]
Sent: Wednesday, December 15, 2004 4:14 PM
To: [log in to unmask]
Subject: Re: [TN] Resistive internal layers
Blair,
Yes the lead resistance was taken into account.
Phil.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Blair K. Hogg
Sent: Thursday, 16 December 2004 12:04 AM
To: [log in to unmask]
Subject: Re: [TN] Resistive internal layers
Phil,
I'm curious, when you measured these did you use a 4-wire meter or some
other method to eliminate the meter lead resistance?
Blair
>>> [log in to unmask] 12/14/04 07:26PM >>>
Just some further findings on this particular problem;
There are four through hole connector pads (A,B,C,D) in a row, each pad 0.8
inches from the next pad. There is a 6 thou, half ounce track (same internal
layer) running in parallel with the four pins, about 100 thou from the pads.
The four pins are connected to the pads with stubs. IE: the traces do not go
through the pads
The resistance measurements are as follows:
A to B = 1.2 ohms
B to C = 1.2 ohms
C to D = 1.2 ohms
A to C = 2.5 ohms
B to D = 2.5 ohms
A to D = 3.7 ohms
Which makes the trace stub and pad/via resistance approx 0.05 ohms And the
parallel trace resistance between any two adjacent pins approx 1.2 ohms
The other internal layer is the same, but the A to D resistance is 2.4 ohms
Some other PCBs show approx identical resistances
While others have different resistance but the same ratios
Some are OK
None of the external traces show this effect. Even those going through vias
from the top to the bottom of the PCB.
regards,
Phil.
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