Tightening down the tolerance gets expensive and can effect
the PCB yields considerably. Maybe the nominal value should
be offset alittle. i.e., I've seen 55 Ohms called out and when
I asked the customer why 55? They said that the "lump sum"
was 50 Ohms including pad capacitance and all (Measured by
Network Analyser on the "Critical" Traces). But the single
ended TDR target was 55 Ohms. There was no price difference
of just shifting the nominal.

Dave
-----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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