Reverse breakdown of BE junction: damaging current?

[dom0]

So ... the reverse breakdown of the BE junction of BJTs is well-known. What doesn't seem to be well-known is how high the breakdown current must be to permanently degrade the part. I read some vague references like "Beta is permanently lowered at low reverse currents" and the like, but nothing solid. Does that mean µA? A few hundred nA? So, what's the maximum reasonable reverse ib for your average few-hundred mA ic, couple-dozen V Uces low power transistor like a 2N2222 or a BC337?

[T3sl4co1l]

Depends on the extent of damage.  I've never seen data on how fast the damage accumulates (presumably, it's a dosage measured linearly by charge), and to what currents it causes problems at (presumably, higher doses cause a higher current threshold effect?); you'd have to run trials yourself to see.

Also interesting to see, would be the effect on low frequency noise (0.1-1000Hz?).

Supposedly, it can also be partially annealed at soldering temperatures.

Maximum safe level?  Vebo is measured at 10uA, but beyond that, Idunno.  To what end?  If you want a good zener, get a real one; much less noise, and guaranteed voltage level.  If for repetitive conditions in an amplifier or switching circuit, use an antiparallel (E-B) protection diode (or a lower voltage bidirectional TVS, or a series prevention diode).

Tim

[dom0]

Thanks for the answer. It still does surprise me that no one ever collected this data, but then again countermeasures are usually simple or not needed at all by design.

[nqtronix]

I've used the BE breakdown of the BC807/817 to protect the gate of (slow switching) mosfets a few times. They break down relative precisly at 8V, which is good enough for me. Considering a typical zener diode withstands several mA witout issues I decided to go up to 1mA BE reverse current. Till now it works fine. If you don't care about the accuracy of the breakdown voltage, b
and just need a relativly current independed voltage drop like the 0.7V pn diode drop then go for it, else get a zener diode.

[edavid]

So ... the reverse breakdown of the BE junction of BJTs is well-known. What doesn't seem to be well-known is how high the breakdown current must be to permanently degrade the part. I read some vague references like "Beta is permanently lowered at low reverse currents" and the like, but nothing solid. Does that mean µA? A few hundred nA? So, what's the maximum reasonable reverse ib for your average few-hundred mA ic, couple-dozen V Uces low power transistor like a 2N2222 or a BC337?

Zero tolerance!

(I just don't see any reason why there would be a threshold.)

See also: https://www.eevblog.com/forum/projects/bjt-ce-breakdown-permanent-degradation/msg633836/#msg633836 and later posts in that thread