Patrick McCluskey, Kofi Mensah and Casey O'Connor
CALCE Electronic Products and Systems Center
University of Maryland, College Park, MD 20742
Dexter Electronic Materials
Over 97% of all integrated circuits produced today are available only in plastic encapsulated, surface mountable, commercial grade or industrial grade versions. This is especially true for the most advanced technologies, such as high-speed microprocessors. The cost, availability, and functionality advantages of these devices are causing many electronics manufacturers to consider using them in elevated temperature applications such as avionics and automotive under-hood electronic systems to ensure early affordable access to leading edge technology. However, manufacturers only guarantee the operation of commercial devices in the 0oC to 70oC temperature range, and industrial devices in the -40oC to 85oC temperature range.
This paper describes the first study which addresses the reliability of plastic encapsulated microcircuits (PEMs) in the range from 125oC to 300oC , well outside the manufacturer's suggested temperature limits. Previous work has indicated that PEMs sold for use in the commercial and industrial temperature ranges can often operate within the manufacturer's suggested electrical parameter specifications at much higher temperatures. For example, in this study the Motorola MC68332 microcontroller, which is widely used in avionic systems, remained fully functional to 180oC . This is in accordance with previous work that indicated no fundamental constraints to the operation of silicon devices at temperatures up to 200oC . However, this study also revealed that industrial grade, plastic encapsulated MC68332 devices had less than half the lifespan at 180oC than similar MC68332 devices packaged in hermetic ceramic packages. In addition to the MC68332, the other nine types of plastic components studied had a shorter lifespan at 180oC than their ceramic packaged counterparts. Outgassing of flame retardants with the associated catalysis of the growth of intermetallics was determined to be the principal cause of failure in the plastic components.
Further studies conducted on 84-lead plastic quad flatpack (PQFP) lead frames encapsulated in two different molding compounds revealed that the plastic encapsulant itself begins to lose its ability to insulate leads at temperatures greater than 250oC and can actually combust at temperatures greater than 300oC . Both insulation resistance degradation and cracking were found to be more prevalent in novalac than biphenyl. In summary, these studies have shown that while plastic encapsulated microelectronics can operate at temperatures above 125oC , they have less than half the life of ceramic microcircuits at 180oC and they begin to show signs of insulation resistance degradation after 300 hours at 250oC .
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