Plastic encapsulated device

Over 95% of all the microcircuits made are packaged in plastic, usually a transfer moulded epoxy resin. Changes in packaging technology will occur away from the familiar PDIP (plastic dual-in-line package) to smaller SOT or chip carrier formats but plastics will continue to be the dominant packaging material for cost reasons. At the same time there is a need to improve the reliability of plastic encapsulated devices (PEDs) as they find further use in professional and certain military applications. 

Since absorption and permeation of water through polymer materials are inevitable, the most serious problem in plastic encapsulated devices is aluminum metallization corrosion in moist atmospheres, which leads to functional failures of the devices... 

Harrison, J. C., Long term reliability of plastic encapsulated devices through control of the encapsulation material. Proceedings of Symposium on Plastic Encapsulated Semiconductor Components, Malvern, 1976. 

A number of factors have enabled the economies in cost possible with the use of plastic packaged devices to be realised. The development of new grades with freedom from the ionisable impurities that could result in corrosion problems when transported to the chip surface by water permeation, the incorporation of corrosion inhibitors, the careful selection of plastic material (to avoid thermal expansion mismatches with resulting stresses on the chips) and the reduction in life expectancy of current equipment due to the rapid rate of development and outdaring of equipment associated with the new silicon technology has now resulted in plastic encapsulated devices dominating the component field. 

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