Hi Mitch!
Thanks for the quick response!
As regards the IPC specs, one of my old friends and former colleague
Rich Mellitz did a lot of work for the IPC specs in the area of TDR and
impedance measurement. Rich is a stickler on Z0 measurement accuracy.
Rich, if you're out there - Hi!!!!!
We do Z0 testing on all our protos. This is in addition to work the
board shop does. The TDR setup we use launches a 30-35ps risetime pulse
with a 1/2 volt step. In addition to the Z0 itself, we take delay
measurements as well as watch the risetime at coupon launch and at
coupon exit. The measurement procedure is critical for accuracy.
Other test beds may do slower as you mention (200ps).
One thing I noticed was that you specified a slower pulse, i.e. in
microseconds. How does this benefit you?
Regards
Gerry
-----Original Message-----
From: Mitch Morey [SMTP:[log in to unmask]]
Sent: Thursday, May 21, 1998 2:55 PM
To: [log in to unmask]
Subject: Re: [TN] Frequency problems with FR-4
Gerry,
I might have gotten the "values" mixed up. I think I intended to say the
testing was requested to be done at 20us (micro) instead of the usual
200ps (picoseconds), not Db. Sorry for the confusion. I've been going
around my office looking for the fabrication drawing this was specified
on, but I can't find it. I hope I'm right this time. Best to talk with a
fab house
about impedance testing issues. Our fab house at that time couldn't test
to the higher spped, so they had to have it done somewhere else.
Also, ask for the certification on your fab drawing. They will supply it
to
you, if they DO do it.
But, A great reference spec for impedance testing, unless you use the
IPC-TM-650, is IPC-2141 (design for High Speed applications)
Thanks for the input.
Mitch
>>> "Gerald G. Gagnon" <[log in to unmask]> 05/21/98
09:22am >>>
Hello Mitch
You wrote:
Snip....
One thing we did was ask for impedance testing to be done to
200db levels instead of the standard 20db. This would show any and all
discontinuities along the traces.
Snip.....
Question: With the impedance measurement techniques I've seen, this
parameter is not mentioned. How does one determine
from a given procedure, the dB level of the
particular test they are running?
BTW, I agree with your assertion that FR4 can be used with significant
signal content in the 1Ghz range.
Regards
Gerry
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