How Mosfets Burn Out with Heat

[D from BC]

In my experience, overheating Mosfets fail with all the pins shorting
out.
I guess the mosfet turns into a conductive blob.
Then the currents can 'take out' other electronics too.
Poof...then poof...and poof..until something breaks the loop.

Is this a typical fail mode?


D from BC
British Columbia
Canada.

 

[MooseFET]

In my experience, overheating Mosfets fail with all the pins shorting
out.
I guess the mosfet turns into a conductive blob.
Then the currents can 'take out' other electronics too.
Poof...then poof...and poof..until something breaks the loop.

Is this a typical fail mode?

A MOSFET can fail in an overheating manner that ends up as a shorted
blob. You can also punch the gate oxide and get a resistance from the
gate to the channel. If you apply too high of a dV/dt at the edge of
turn off you can get a reduced drain breakdown voltage etc.

 

[Joerg]

In my experience, overheating Mosfets fail with all the pins shorting
out.

I have seen some where one pin was _gone_. Seriously.

 

[Winfield]

In my experience, overheating Mosfets fail with all
the pins shorting out. I guess the mosfet turns into
a conductive blob. Then the currents can 'take out'
other electronics too. Poof...then poof...and poof..
until something breaks the loop.

Is this a typical fail mode?

You may want to check a bit more carefully. In my
experience a common overheating failure mode is a
gate-drain short. This means the MOSFET turns on
from the drain voltage and stays on hard enough to
pull the drain voltage down to about Vgs=5V, etc.
While you could call that a "short," it's actually
a slightly specialized version of a short.

 

[Spehro Pefhany]

I have seen some where one pin was _gone_. Seriously.

In that case, they tend to fail open.


Best regards,
Spehro Pefhany

 

[John Larkin]

In that case, they tend to fail open.

ftp://66.117.156.8/ExFets.jpg


John

 

[D from BC]

ftp://66.117.156.8/ExFets.jpg


John

Nice collection...
"
I call this one 'Poppy'.
And I've named this one 'Cracky'.
That's 'Snappy'.
And that one is 'Poofy'....."


A good reason to wear eye protection. *;(

Most circuits I make can't draw enough power for an explosion but seem
to have enough power to 'blobbify' the die.


D from BC
British Columbia
Canada.

 

[D from BC]

You may want to check a bit more carefully. In my
experience a common overheating failure mode is a
gate-drain short. This means the MOSFET turns on
from the drain voltage and stays on hard enough to
pull the drain voltage down to about Vgs=5V, etc.
While you could call that a "short," it's actually
a slightly specialized version of a short.

I'll check for that in the future..
It just seems I discover 3 pins shorted out more often than just 2
pins.

For example:
I recently killed a FCPF11N60 TO220.
No external damage. Removed from circuit.

Gate to Drain: 2ohm
Gate to Source: 2ohm
Drain to Source: 0.1ohm (probe wire resistance)

However, this one didn't die due to a slow rise in temperature.
That mosfet was working fine until I goofed up a test.
It fried instantly after power up.


D from BC
British Columbia
Canada.

 

[legg]

In my experience, overheating Mosfets fail with all the pins shorting
out.
I guess the mosfet turns into a conductive blob.
Then the currents can 'take out' other electronics too.
Poof...then poof...and poof..until something breaks the loop.

Is this a typical fail mode?

It's a typical end result of all failure modes, if bonding wires don't
fuse first.

Mosfets will still function at temperatures where the die-bond solder
is liqufied and migrating out of the pckage seams.

You're supposed to be able to recognise these temperatures before this
happens, if all nuts and bolts are secure. It's a detectable and
recoverable condition. (how many times.......?)

RL

 

[Jakthehammer]

150V when it's fully off = 0W
90A when it's fully on (perhaps 0.006ohm) = 48W
15V at 4.5A = 72W

I know that. That's why it doesn't make any sense, I tried IR, VISHAY parts, they all behaved the same. I tried their sample circuit, none of them can survive the Kickback 1.2KW transformer.

Did you provide somewhere for that heat to go?

Yup Fully heatsinked.

 

[Jakthehammer]

150V when it's fully off = 0W
90A when it's fully on (perhaps 0.006ohm) = 48W
15V at 4.5A = 72W

I forgot to mention that I did find the solution for my Mosfet problem, by using 4 MOSFET's, they seemed to be Ok. 4 X 300W = 1200Watts total.

 

[Joerg]

Nice collection...
"
I call this one 'Poppy'.
And I've named this one 'Cracky'.
That's 'Snappy'.
And that one is 'Poofy'....."


A good reason to wear eye protection. *;(

Most circuits I make can't draw enough power for an explosion but seem
to have enough power to 'blobbify' the die.

You never know. On the one with the vaporized leg they thought so, too,
because it was battery operated. But then there was this huge capacitor ...

 

[Jakthehammer]

A MOSFET can fail in an overheating manner that ends up as a shorted
blob. You can also punch the gate oxide and get a resistance from the
gate to the channel. If you apply too high of a dV/dt at the edge of
turn off you can get a reduced drain breakdown voltage etc.

Right but WHY WHY? did they rate it at 90Amps? 150V? I put in only 15V 4.5 amps. How can this overheating the funky MOSFET? Someone lies about their spec.... but who cares, I go with Transistors, they're forgiving than Mosfet.

 

[Clifford Heath]

Right but WHY WHY? did they rate it at 90Amps? 150V? I put in only 15V 4.5 amps.

150V when it's fully off = 0W
90A when it's fully on (perhaps 0.006ohm) = 48W
15V at 4.5A = 72W

Did you provide somewhere for that heat to go?

How can this overheating the funky MOSFET? Someone lies about their spec....

Someone should try to *read* the spec and apply Ohms's law

but who cares, I go with Transistors, they're forgiving than Mosfet.

Not to someone who doesn't read the specs.

 

[Dave Platt]

Right but WHY WHY? did they rate it at 90Amps? 150V? I put in only 15V
4.5 amps. How can this overheating the funky MOSFET? Someone lies
about their spec....

.... or somebody is misreading the spec?

If I recall correctly, MOSFETs which are designed for power-switching
service are spec'ed by their maximum standoff voltage, and their
maximum on-current when driven into full conduction, and their maximum
power dissipation. The latter is *not* the product of maximum voltage
(at zero current) and maximum conduction current (at minimum voltage
drop across the conduction channel).

If you try to use one of these MOSFETs in an application where you
aren't switching it hard-and-fast, you can end up dissipating more
power in the MOSFET junction than you'd expect, and may exceed the
max-dissipation or junction-temperature limits, even if neither the
voltage nor the peak current approaches or exceeds the spec limit.
You end up pushing the part out of its safe operating area, and it
releases its magic blue smoke.

but who cares, I go with Transistors, they're
forgiving than Mosfet.

In some ways, yes, in other important ways no. Bipolar parts have the
same sort of safe-operating-area limitations as MOSFETs. In some ways
they're even more trouble-prone, if you ignore SOA rules, as they're
more prone to second-breakdown thermal runaway.

 

[RRogers]

It's a typical end result of all failure modes, if bonding wires don't
fuse first.

Mosfets will still function at temperatures where the die-bond solder
is liqufied and migrating out of the pckage seams.

You're supposed to be able to recognise these temperatures before this
happens, if all nuts and bolts are secure. It's a detectable and
recoverable condition. (how many times.......?)

RL

Quite right. Drop the drain voltage or pulse the drive, then touch
the FET with your fingers (an instrument that is always available
unless you are really careless) and you should find that the FET is
getting too warm. Having found that, review your circuit carefully;
sketch VI curves, calculate switching losses, check worst case
threshold voltages, etc.........

 

[D from BC]

Quite right. Drop the drain voltage or pulse the drive, then touch
the FET with your fingers (an instrument that is always available
unless you are really careless) and you should find that the FET is
getting too warm. Having found that, review your circuit carefully;
sketch VI curves, calculate switching losses, check worst case
threshold voltages, etc.........

Of course...
But sometimes I get math lazy and just pop in the best guess and let'r
rip..
Then poof!
Most often I find mosfet pins all shorted out after a failure.
Not entirely a bad event
It gives me an idea of how much more 'upstream' damage can happen in
cause of mosfet failure.
Ex. Exploding driver chips.


D from BC
British Columbia
Canada.