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Electronic Design

High-Temperature Glass Used To Seal Diodes

High-temperature sealing of silicon-diode sheets has been achieved with a technique that may provide hermetically sealed semiconductor devices without the use of cans. The method is adaptable to volume production, and tests indicate that excellent surface protection is provided.

The glass-sealing process, developed by International Business Machines Corp.'s Components Div., Poughkeepsie, N.Y., begins with the formation of a silicon-dioxide surface on a silicon wafer, which has been conventionally masked and diffused. Then, a powdered, chemically resistant glass—such as Pyrex, which has a coefficient of thermal expansion about equal to that of silicon—is applied to the oxided surface. The glass then is chemically fused to the oxide surface by heating it to about 845°C.

Yields of 95% to 100% were achieved, according to IBM, using an oxide thickness of 5000 A and glass thickness of 3 microns, with a firing time of 10 min. Individual devices were cut apart with an ultrasonic cutter, and leads were attached through small holes etched through the glass and oxide coating.

Individual planar-diffused diodes made by this technique were subjected to various tests, including the conventional Mil 1-202A, as well as much more severe types. In the military tests, the devices were cycled between 25° and 65°C while 90% to 95% relative humidity was maintained. No devices failed in five months. Diodes tested under 20-V reverse bias and similar environmental conditions did not show any changes after two months of testing, according to IBM researchers. (Electronic Design, October 25, 1961, p. 22)

Glass passivation was a giant step forward in improving the reliability of semiconductor devices.

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