Fred,

Another concern is with the 5 mil lines at 50 ohms. For you microstip
layers (external), you'll only have about 3.5 mils of dielectric material to
the ground/power reference plane! That's a pretty thin dielectric
separation. For your stipline layers (internal) you'll have about a 7 mil
dielectric separation to your reference planes, so that should be ok, but
the external layers might be a concern for you.

Eddie bunker wrote:
(snip) Multek visited Dovertron in Cork (part of the same group of
companies), and good friends of ours too. The article focused on his
warnings that at 300MHZ and above, Fr-4 is unsuitable and future
substrates should be of alternative materials... (snip)

Interesting, coming from manufacturing companies. If I talk to my fab
shops they say there is no costs difference using GETEK material. Might
be interesting to see if Multek feels the same. Next thing, can Multek
supply the data they have to make this determination?

Good luck again,
Mitch Morey

>>> Fred Watt <[log in to unmask]> 05/21/98 07:25am >>>
        Has anybody had any problems with FR-4 at 100 to 200 MHz?  I
have several boards from several fabrication shops in which the signal
loses amplitude above 80-100 MHz.  The boards are controlled
impedance (50 Ohms) with 5 mil traces and 5 mil dielectrics.  The traces
are about 6.5" long.
        I would appreciate any comments on this subject.  The supplier of
the material says that FR-4 should be good to 400 MHz.

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