Relative lifetime prediction for CPV die-attach layers

In concentrating photovoltaics (CPV) cell assemblies, a large-area die-attach layer is subjected to thermal cycles, leading to thermomechanical fatigue. This causes cracking and the eventual failure of the CPV cell by thermal runaway. We define a damage metric representing lumped progress toward failure and present a numerical model for computing the accumulation of damage for arbitrary transient temperature conditions. The model is applied to a particular design with a solder dieattach layer. We show that accelerated-test thermal cycles with higher ramp rates cause more damage, both per cycle and per unit time. Outdoor exposure to one entire year in two geographic locations is also simulated, revealing that a year of exposure in Golden, Colorado is equivalent to 1.4 years of exposure in Oak Ridge, Tennessee.