Silicon power transistors of the n⁺-p-n-n⁺ type have been developed for automotive applications. In order to obtain highly reliable performance under the severe environmental conditions usual in such applications, the characteristics of power transistors having a high degree of second-breakdown resistibility were investigated and a method of evaluating such transistors was developed. A nondestructive method of evaluating resistibility to “thermal-mode” second-breakdown that uses the characteristic change in the current gain hFE of a transistor has been developed and applied to optimize the design of devices for automotive applications. The resistibility to “thermal-mode” second-breakdown of power transistor chips in hybrid integrated circuits was evaluated with this new method. It became clear that the thermal conditions between a chip and its almina substrate could be optimized to improve the resistibility to “thermal-mode” second-breakdown. Many kinds of automotive equipment that includes power transistors with a high degree of second-breakdown resistibility has been put to practical use in actual automobiles.

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