RE: [SI-LIST] : High-Speed Materials {[DC] & SI-List}

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From: Zabinski, Patrick J. (zabinski.patrick@mayo.edu)
Date: Thu Feb 03 2000 - 10:16:16 PST


Alexis,

We have tried several such materials, and some of them
have worked out "fine". However, nearly all of the
PTFE-based (teflon) materials have presented problems with
adhesion, rigidity, and/or strength; their electrical properties
have been good, but their mechanical properties were less
than optimal.

If you're looking at Getek, I suggest looking at similar
materials from other sources (e.g., Nelco). Several other
companies are making competing materials at lower cost.

One point to keep in mind: the dielectric is not the only
limiting factor at the higher frequencies; the conductor
loss generally becomes a bigger factor with the materials
that with standard FR4. I'm not sure of the details, but
to obtain the same peel-strength with the non-FR4 materials,
some (not all) of the materials use a larger toothing profile
(i.e., surface roughness) than FR4, which can really eat away
at your signals. So, even though your dielectric losses
are better, the rougher metal increases your conductor
loss. When looking at the various materials, be sure
to keep this in mind.

From my personal experience, the Getek, Nelco, etc. materials
are marginally better that standard-FR4, but I have yet
to be convinced that PTFE-based materials are worth the
cost/mechanical-weakness for complex multi-layer boards.

Pat

>
> We are currently researching materials that will handle
> high-speed circuits
> (over 1 ghz) better than the current FR4 that we've been
> using. We've talked
> to our fab vendors and they are recommending alternatives
> such as Getek,
> Tetra 2, and Rogers 4350. Now I'd like to hear from the end users. Has
> anyone out there gone through a similar transition? What were your
> experiences with the more costly materials? Any input would be greatly
> appreciated.
>
>

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