Forums

C0G ceramics vs humidity---I think I have the answer

Started by Badbob April 10, 2015
Follow my logic:

The reason a polymer capacitor drifts with a change in humidity is that 
water is a very polar molecule w/ a dielectric constant of about 80. 
Polymers are much lower, 2-8 more or less.

Add .1% water to the plastic and you get a large change in d constant, 
around 4%.

C0G material has a constant that varies but usually similar to water. 
Add .1% water and you get a change around .1%.

That even assumes C0G will absorb that much water.  So the answer is 
yes, C0G could drift with humidity but it can't be much.

I was reading some papers on plastics, humidity etc. and it sort of came 
together.

Bob
On Friday, April 10, 2015 at 10:40:56 AM UTC-7, Badbob wrote:
> Follow my logic: > > The reason a polymer capacitor drifts with a change in humidity is that > water is a very polar molecule w/ a dielectric constant of about 80. > Polymers are much lower, 2-8 more or less. > > Add .1% water to the plastic and you get a large change in d constant, > around 4%. > > C0G material has a constant that varies but usually similar to water. > Add .1% water and you get a change around .1%.
This, I don't see. C0G is a temperature characteristic, there's potentially dozens to hundreds of different ceramic formulations that achieve that characteristic. The ceramics could have chemical (composition change) or physical (swells when wet) or even erosion response to moisture. The usual ceramics do NOT absorb moisture, because sintering to high temperatures, the bonding is stronger than one expects from wetting forces. The metal electrodes, and a paint layer, on the other hand, are in contact with the ceramic and cycle through liquid-solder temperatures. That's why 0.1% measurement of a capacitor is unlikely to tell you what value it has after soldering. And 0.1% deviation in an AC signal only makes about a 0.009 dB difference...