Nora, here are two proposed models that have been used to determine the
accelerated life of a PCB under Temperature, Humidity and Voltage. In each
case no values for constantans are given since these are material and design
dependant.

 1)  MTTF = ax[1 + bx(L*n)/V]  x(RH*c) x exp (E/(RxT))

      by T.L. WElsher etal, International Reliability Physics, 1980 pp 39-43

 2)   MTTF = a x(RH*b) xexp (E/(RxT)) + dx(L*2)/V)

      by J.P. Mitchel etal, Proceedings Printed Circuit World Convention II,
1981, 
      pp 80-93

where MTTF = Mean Time To Failure
          a, b, n, c,  d are all constants to be determined experimentally
for a given product, L conductor spacing, V applied DC voltage, RH relative
Humidity, R is gas constant and T absolute temperature, E is activation
energy.

Pratap Singh
RAMP Labs
(512) 255-6820

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