THB reliability models and life prediction for intermittently-powered nonhermetic components

Results of temperature-humidity-bias (THB) acceleration experiments are often expressed in terms of a power-law function of relative humidity and an Arrhenius temperature dependence (Peck's model). For steady-state operation, we show how to calculate the effect of power dissipation on service life (or its reciprocal, acceleration). We derive an interesting inequality involving Peck model parameters which determines whether a moisture-related mechanism is accelerated or decelerated by increased power dissipation. For intermittently-powered components the steady-state acceleration is multiplied by a time-on factor (TOF). We introduce a new, broadly applicable, formula for the TOF. The formula involves thermodynamic properties of the molding compound encapsulating the die. The formula applies to most plastic encapsulated devices under typical "use" conditions.<>