Comparison of plastic and hermetic microcircuits under temperature cycling and temperature humidity bias

Plastic and hermetic integrated circuits, as discrete packages and as assembled on circuit card assemblies, were temperature cycled between -55 and +85°C through 1000 cycles, and 26 parametric values were observed in terms of failure rates or shifts. The circuit card assemblies were then tested for up to 650 h at 85°C-85% relative humidity (RH). Circuit cards were also assembled using both plastic and hermetic versions of a custom IC, for comparison with each other as well as with an older discrete version of the card, which had a history of reliable operation for over 20 years. The IC version of the cards were coated with either urethane or parylene and, along with unassembled ICs, were tested for 1000 h at 85°C-85% RH with intermittent bias temperature, humidity, bias (THB). Conservative lifetime estimates, for both the plastic and the ceramic ICs, for avionics applications, were determined to be well over 20 years. It is concluded that, in this and similar applications, there is no reliability advantage for either plastic or ceramic ICs