Secondary breakdown
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Secondary breakdown is a catastrophic thermal failure mechanism of semiconductor devices, supposed to be the result of current concentration ("current crowding") which then causes the junction temperature locally to exceed the maximum limit. It is an independent failure mechanism, not the result of any other failure mechanism.
To prevent its occurrence in service, the manufacturer defines a Safe Operating Area (SOA) for the semiconductor device, usually in terms of a family of I/V curves with pulse duration as a parameter.
The possibility of secondary breakdown is inherent in bipolar junction transistors, for example, although the SOA varies with the type of construction of the device, and can be optimized by suitable geometric layout. Some types of semiconductor devices do not suffer the problem.
