Diode Failure: Causes & Effects

[Shadrack]

Does anyone have any information on diode failure? I'm interested in knowing how diodes can fail and what happens when they do fail.

Specifically, what conditions of a diode will cause it to fail to be a closed circuit either direction criteria (like, become as useful as a wire)?

 

[NoTime]

Voltage transients tend to cause the wire effect.
Overcurrent tends to cause an open, like blown fuse.
On rare occasions you can get states between these extreams.

What happens depends failure mode and on what its being used for.

 

[berkeman]

Take a look at the full diode curve, including both the forward bias area and the reverse avalance breakdown area. Both of those areas can result in significant power dissipation, where you have both voltage and current at the same time. That power dissipation causes heating, which in the forward conduction region lowers the forward voltage and increases the forward current. I'm not sure what increased temperature does in the reverse avalance region offhand -- probably helps to limit it since avalanche is related to mean free path. Also in the forward bias region, heating and the positive tempco effects can cause current bunching, which accelerates failure modes.

In my experience, the heating first melts the silicon (in the current bunching areas), which then looks like a low-impedance short. If there is sufficient power from the source, the fail-short will blow open as a fail-open. If there is not sufficient power from the source, it will likely stay a fail-short.

The maximum junction temperature is one key to calculating whether you are at risk for failure. There are also SOA considerations, and the geometry of a power diode construction can help to ease the current bunching issue.

 

[Shadrack]

Thanks for the input NoTime and berkeman!

I will need to study the curves of the diode in question to see what could possibly be occurring. Is it possible that being in a high-temperature enviornment over the span of years will causs a melt in the silicone that will causs a low-impedance short? Or are we looking at a momentary high-temperature condition that is at the melting point of silicone?

I wonder what the melting point of silicone is...

 

[NoTime]

High temps with current over years will affect the impurity diffusion in the device structure and destroy the junction properties.

Don't know if it's the same as melting point, but outright junction failure will occur somewhere around 190c in silicon.