Fancy PCB materials--wisdom?

Phil Hobbs · 2013-03-27T20:41:19+00:00

Hi, all, So I've designed this front end for a surface voltage tool for testing silicon wafers. Since the input is uber-high-Z, it needs to keep the stray capacitance very low and very stable, so it has a fancy bootstrapped input stage and a bootstrapped shield connected to a bootstrapped reference plane. I'd like very much to reduce the board capacitance. Naturally I thought of using a fluorocarbon circuit board material, but no, the really low epsilon ones all seem to be PTFE, which has a glass transition at room temperature, and so is horribly unstable. Any favourite low-epsilon materials with high surface resistance and good stability near room temperature, that won't cost the earth or give the board house conniptions? Thanks Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net

Mar 27, 2013 40 Replies

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josephkk 13 years ago

No board. Low k ceramics and air. Maybe you can get some "0 pF" 0402s to substitute for standoff insulators. Hmmm

AVX has a nice selection of low value COG caps in various packages, intentionally tombstone some of these and build your circuit on the other ends and include device C in the circuit. You could even include mounts for "shield" planes. Ultra low c/ft triax.

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