Moisture uptake and chemical compatibility of semiconductor plastic encapsulant materials

Moisture uptake of semiconductor devices encapsulated in five different mold compounds in routine production was determined gravimetrically and control charted over a two-year production period. Mean moisture uptake and associated 3σ upper control limits ranged from a low of 0.29 and 0.52 weight percent to 0.40 and 0.82 weight percent, respectively. Two of the mold compounds studied were not capable statistically of published specification maxima for moisture uptake. The compatibility of three mold compounds with different chemicals was determined at 25°C and at boiling temperature. Weight change of units ranged from a maximum increase of 0.18% in boiling JP8 jet fuel to a maximum loss of 0.19% in boiling Ionox FCR alcohol. Dimensional changes ranged from a maximum increase of 0.58% to a maximum decrease of 0.78%. In a third aspect of this study, 90 units were subjected to natural temperature/pressure cycles from sea level to altitudes of 41,000 feet, during 168 flights of a business jet aircraft across the US. The effects of these conditions on glass transition temperature, coefficients of thermal expansion and physical integrity of the units were determined