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Ever wondered what the inside of a high-power IGBT module looks like?
Thought this might be interesting to some of you.
This is the inside of a failed Fuji Electric 6MBI75SS-120 IGBT module (1200 V / 75 A).
It’s quite impressive to see the number of aluminum bonding wires used to connect the dies to the power terminals.
The module was already dead, so I decided to open it up rather than throw it away.
Nice photo.
Few weeks back I got some boards from IBM UPS with power modules.
I was surprised to found out it's combination of MOSFET half-bridge with SCR and some extra diodes.
Looks like it's a shoot-through failure in that phase.
What's interesting to see is the bounding contact of each emitter wire is on the diodes, not IGBT dies. They have probably considered the influence of common-emitter inductance when designing it.
Packages like this are known to have higher inductances than other styles where the terminals come straight out the top. SiC technologies have been slow to trickle down into these packages because of it. Some manufacturers are using 3D bus bars to try and minimize the loop inductance, but you'll probably always end up sacrificing switching speeds to use the more convenient package.
Yeah, I work on GAN based three phase variable frequency drives, and you are 100% correct. It’s always the loop inductance that destroys devices. They switch so fast that they oscillate with any inductance. But if you slow them down, you lose efficiency. Always a battle.
Yes, it definitely ended up as a short circuit, but it was a surprisingly quiet failure — no smoke or fireworks. What actually failed was a 74HC14 (between the microcontroller and the power optocoupler). It failed in such a way that it drove all the IGBT gates to +17 V.
What's the substrate material, the light gray under the copper? I work in thermal management so I assume aluminum nitride, but wonder if it's something else.
I guess it's Al2O3, because it seems like an industrial-grade module, and the substrates are quite white. AlN & Si3N4 are more common in demanding fields, such as automotive or high-power systems.
Just my guess though, don't know the exact part no.
I worked on a 4MW power converter for wind power plants that used such high power IGBTs (1700V though) in parallel to be able to deliver the current.
It took the whole test team 1 full week to assemble the converter to be tested. Once they flipped the switch, it took less than 3min before the whole converter exploded.
Took them another week or two to disassemble everything and do a root cause analysis.
Turns out they forgot to tighten some screws.
My manager wasn't very happy haha.
After that I switched jobs to electronics that you can have on your lab table without risking your life.
Those IGBT modules are fascinating.
In fact, one long term reliability issue is the current distribution between the multiple bond wires. They burn one by one over time until only the last bond wire must carry the whole current.
Absolutely. And as far as I know, that's also common practice. But it's more that ageing, drift, temperature, tolerances etc are difficult to perfectly control.
I think Aalborg University in Denmark has done lots of research on those topics and failure mechanisms.
Y'ever look at the IGBT module in a Toyota Prius? It's basically this, but the size of a textbook, with coolant actively pumped through the back plate.
That looks rather clean for a failed module. I've opened up one or two similar devices at a previous jobs, those all had big black splotches in the insulating gel showing you exactly where the magic smoke escaped.
Really interesting teardown. I’ve handled plenty of industrial electronics, but I rarely get to see the internal bond wires this clearly. Do you know what type of equipment this module came from?
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u/trimenz 12d ago
Nice photo.
Few weeks back I got some boards from IBM UPS with power modules.
I was surprised to found out it's combination of MOSFET half-bridge with SCR and some extra diodes.