[log in to unmask] asks:

Does anyone have any information on the affects that the soldering 
process has on X7R or Z5U type dielectric capacitors? What change in 
capacitance can be expected due to the result of capacitor aging?

**************************

According to Howard W. Johnson and Martin Graham in their book entitled
"High-Speed Digital Design, A Handbook of Black Magic":

Z5U and X7R capacitors decrease in value at a rate that is proportional to the 
logarithm of time since firing.  SOLDERING A CHIP CAPACITOR RESETS ITS AGING 
CLOCK.

Z5U ages at a rate of about -2% per decade.  Preaging the caps for 100 hours or so ensures no more than an additional 2% loss of capacitance over the next 
1,000 hours, another 2% loss over the next 10,000 hours and so on.  Temperature
derating is horrible with Z5U.  Vitramon quotes a +22 to -56% variation over 
the range of 10 to 85 degrees C.  Below 10 degrees C Z5U is not recommended.  
Summing the initial tolerance, ageing for 100,000 hours, and a temperature of 
10 degrees C, we lose 2/3 of the advertised capacitance value.

X7R ages at a rate of about -1% per decade.  X7R has a lower dielectric 
constant than Z5U, but better temperature and aging properties.  Temperature
derating for the X7R material is +/-15% over the range -55 to 125 degrees C.
Between the initial tolerance (10%), ageing for 100,000 hours, and a temperature
of +/-55 degrees C, we lose only 29% of the advertised capacitance value.

It should be apparent from the difference in dielectric that more capacitance
can be had in a smaller package with the Z5U material.  However, it is also
the least stable material as described above.

Gary P.
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                                  Gary D. Peterson
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