RH Function Based on Pore Distribution

RH Function Based on Pore Distribution. Anotherway of expressing the relative humidity effect on metal migration is derived from the assumption that a surface or an interface between a film and a substrate can be imagined as consisting of a log-normally distributed pore-network in which water condensation will first occur in the smaller pores as the 

Equation 13 is assumed to be the probability to have a water path. Substituting r from Eq. 12 into Eq. 13, we express such probability in terms of relative humidity, temperature, water surface tension  

Note that since RH replaces the variable r and full condensation is assumed In all pores (not just up to f) when RH = 1, Eq. 14 had to drop the 1/2 coefficient, thus conforming to the conditions P(RH) = 1 whenRH = 1, P(RH) = 0 when RH = 0. 

Both models, Eqs. 11 and 15, are functions of the same three test variables and both have been used to interpret the results of Ag migration in vehicles having epoxy and silicone backseals. The models have been used to project electric failures (due to Ag dendrites grown under accelerated test conditions) to field conditions, thus allowing the calculations of failure rate based on a distribution of fails in time. 

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