Dielectric Constant of Polymers vs. Temperature

May 25, 2004 1 Replies
T

I am trying to measure the capacitance of a small component over temperature, from about -40 to about 120 C. I have tested the bare fixture, and its capacitance seems to change by about 5% over this temperature range. As an example the fixturing changes from about 220 to about 200 fF (decreases as temp increases)



I think that this change might be from the plastic pieces of the fixture (PCB boards, cable insulation) changing dielectric constant over temperature. I looked for dielectric constant over temperature data for polymers but have not hae much luck.



Can anyone recommend a source (pref on the web) with data for dielectric constant over temperature for some polymers? Does anyone have a source for a discussion of this effect?



Thanks in advance,



Andrew


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P

Have you dried out the board? Water has a dielectric constant of 80 at low frequency, so it doesn't take much water to cause problems like this.

The capacitance change is a combination of dimensional change (CTE) and dielectric constant change. Polymers have very large CTEs, probably enough to dominate the TC of dielectric constant.

Cheers,

Phil Hobbs

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