I have seen great responses to your question but the first place to look is
your measurement tool.

I would run a gauge R&R first. Make sure the system is stable and capable.
Buy a 50 ohm reference standard. Plot periodic standard measurements and
only calibrate when the chart shows an out of control situation.

Impedance is tough to measure accurately as the cables, probe and technique
easily skew the results. The best system is a very short cable and the
ground pin fixed to the probe. This needs a coupon with the pads laid out
the same way, but it's worth it. Polar makes a simple to operate and
accurate machine.

Also, the length of the trace and whether it is straight is another critical
factor. Try to measure a coupon, then a trace on the same board.

You should not tighten the spec until you prove it is possible.

Steve



-----Original Message-----
From: Ken Patel [mailto:[log in to unmask]]
Sent: Thursday, August 26, 1999 2:51 PM
To: [log in to unmask]
Subject: [TN] Any connection: Impedance Control value & RF Board


Experts,
We have couple of RF boards which are relatively new to us. Many times, we
have to replace passive components to make it work. Hence, I have this
hypothetical question for you. Is it due to not having correct impedance
value even though measured value on coupon falls within 50+/-10 ohms%? Do
you think we may to have tighten our current impedance specification
(50+/-10 ohms%) if there is a relationship?

Being a mechanical kind of guy this question may sound stupid! Hope to hear
from many of you.

re,
ken patel
______________________________________________________
Ken Patel                       Phone:  (408) 490-6804
1708 McCarthy Blvd.             Fax:    (408) 490-6859
Milpitas, CA 95035              Beeper: (888) 769-1808

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