From: rbmccammon@mmm.com (Roy McCammon)
Newsgroups: sci.electronics.components,sci.electronics.basics
Subject: Re: capacitor materials...what's the diff??
Date: 3 May 1996 16:28:16 GMT
Organization: 3M

There are many differnet types of capacitor material because no material
provides the best performence in every regard.

Here is a quick list of some of the characteristics.  You can find worse
and better units in each type.  I'm shooting from the hip, not looking 
anything up, so I may be wrong on some of the particulars.

Aluminium Electrolytics:
1. Cheap per farad
2. Small per farad
3. Drifty
4. Limited life (they dry out, especially if hot)
5. Leaky
6. Poor at mid and high freq.  Some designers won't use them in a high fi
   audio path.  Generally seen in power supplies.
7. Tolerance: poor
8. temperature range: restricted

Tantalum Electrolytics
1. Cheap, but not as cheap as Alum
2. Small, but not as small as alum
3. Drifty, but better than alum
4. Better life than Alum
5. Less leaky than alum
6. Good up to high audio freqs.
7. Tolerance: better than alum
8. temperature range: better than alum,

PolyEster (mylar)
3. much less drifty than electrolytics
4. much longer life
5. very low leakage
6. usable up to RF
7. Fairly tight tolerence available
8. temperature range: good at low temps, can melt at high temp

Ceraminc.  There are many kinds, I'll call them low, medium, and high.
                 Low 
1. Cost:         high per farad               
2. Size          large per farad
3. Drift:        among the best
4. Life:         long
5. Leakage:      very low
6. Usable freqs: RF
7. Tolerence:    very tight
8. temperature range: wide
9. Voltage:      very high available

                 Medium               

3. Drift:        better than electrolytic, worse than polyester
4. Life:         long
5. Leakage:      low
6. Usable freqs: RF
7. Tolerence:    moderate
8. temperature range: wide

                 High                
3. Drift:        very
4. Life:         long
5. Leakage:      low probably (not sure)
6. Usable freqs: low RF
7. Tolerence:    medium to poor
8. temperature range:restricted high and low

This is not an exhaustive list of types or significant parameters.


Opinions expressed herein are my own and may not represent those of my employer.