Cold temperature failures of the older 2N2222A and 2N2907A transistors led to the discovery of a major manufacturing defect. Some manufacturers were connecting the collector wire with a point contact in the TO-18 headers. The connection would be held in place by filling the bottom of the header with a glass sealing powder.
The collector lead connection to the header, and thus the connection to the transistor die, was a pressure point contact (see Photos A & B) that was held fast by the contraction of the sealing glass during formation of the seal. The failure was seen after hours of cold soaking the equipment without power and then applying power at low temperature. Open collector circuits were found causing catastrophic failure.
The construction design of some other manufacturers had…
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CQ Amateur Radio (Digital) - 1 Issue, December 2022