Hi Ken,

Sounds to me like the design is marginal and has not taken tolerances into
account. These tolerances can be either component tolerances or board dielectric
constant / manufacturing (trace topology) tolerances.

Do you have the same problem with the same batch of boards? With the same batch
of components? Across different batches of each? These factors give you a clue
about where the marginal design exists.

Normal impedance tolerance on a manufactured board would be +/- 5 percent - a
ten percent tolerance might be enough to stop something working but I would put
that in the "marginal design" bracket.

Do you have access to the design engineers? They would have lived with something
like this in their development and are probably very familiar with your problem.
However, getting them to admit that might be problematical  :-)

Cheers

    Andy Kowalewski
    NEC Amrica, Inc.


____________________Reply Separator____________________
Subject:    [TN] Any connection: Impedance Control value & RF Board
Author: Ken Patel <[log in to unmask]>
Date:       8/26/99 2:50 PM

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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