Standard Tests for IGBT Inverter Packages

[mattysiebs]

Hi, new Forum member here!  Decided it was FINALLY time I join and ask some questions seeing as I'm running up against a real quandary here.

So, context:  I work for an electronics assembly materials company (develops solder paste, sinter materials, epoxies, etc) and I work on customer applications with the sinter material group.  I have my BS in Mechanical Engineering from the University of Maryland for additional context.

One of my projects involves a novel double sided inverter module for a company (name disclosed) and I am getting some strange feedback from the customer group.  The first pass I made at this project, the modules failed high voltage testing.  Second round, the modules passed high voltage, however they failed in DC testing.

So, my questions are the following:  What are standard tests for IGBT inverters (for electric vehicles, solar power inverters, etc)?  Does high voltage test include switching of the gate for the IGBT or is it a characteristic curve generator?

[MagicSmoker]

Is this HiPot or breakdown voltage testing? If the latter, then this is typically done by shorting the gate to the emitter and applying a steadily increasing but current-limited voltage across the collector-emitter terminals. Once collector current exceeds the datasheet value for off-state leakage that is the breakdown voltage. Optionally, the voltage can be increased until avalanche breakdown occurs.

HiPot testing is also done with a current-limited power supply, except usually all of the active terminals are shorted together and the voltage is applied between them and the baseplate.

DC testing isn't rocket science, either: just apply the proper voltage to the gate-emitter and pass a known current through the collector-emitter. A "fail" can be from the collector-emitter drop being too high as well as the more obvious modes, like letting out the magic smoke.

[mattysiebs]

I guess I must be overthinking this then.  Honestly the worst part is the team I'm working with is horrible at communicating what happened. I only just got as much information as I've shared.

I assumed the DC test was some form of load testing but I could be wrong.

[jmelson]

I guess I must be overthinking this then.  Honestly the worst part is the team I'm working with is horrible at communicating what happened. I only just got as much information as I've shared.

I assumed the DC test was some form of load testing but I could be wrong.

Since your only responsibility here is the soldering process (if I understand correctly) then there are really only two things involved.
The HV testing is probably related to board cleanliness after the soldering and cleaning process.  And, one thing is the boards have to be DRY (!!!) before the test can be performed.  If it fails here, there may be some reside of solder flux left behind.

The DC test could only be affected by the resistivity of the solder.  If the IGBTs are sitting on big "pillows" of solder, instead of being pulled down flush to the copper of the board, that could affect it.  So, possibly, they are applying too much solder to the board.

Just a few guesses based on the very thin details you have given (sounds like that's all they have given YOU)  If they want your company to help, I think they need to tell you a LOT more about what, specifically, is going wrong.  And, maybe the problem is, they have NO IDEA what they are actually doing.

Jon

[MagicSmoker]

...
The DC test could only be affected by the resistivity of the solder.  If the IGBTs are sitting on big "pillows" of solder, instead of being pulled down flush to the copper of the board, that could affect it.  So, possibly, they are applying too much solder to the board.
...

Good point, also a common reason for failing DC testing is the presence of voids in the die attach solder, leading to hot spots. Unfortunately, you need an x-ray inspection system with a wide anode voltage range for that. The OP's mentioning of double-sided dice might make x-ray inspection especially difficult, however.

[mattysiebs]

Since your only responsibility here is the soldering process (if I understand correctly) then there are really only two things involved.
The HV testing is probably related to board cleanliness after the soldering and cleaning process.  And, one thing is the boards have to be DRY (!!!) before the test can be performed.  If it fails here, there may be some reside of solder flux left behind.
[/quote]

Clarification:  not soldering, rather sintered die attach.  Pretty cool tech with a bunch of advantages over solder.  I have plenty of information about that if you are curious!

So my understanding (after chasing the issue for a little), the high voltage test used a curve tracer (presumably to plot I V curves at varying gate voltages) and the failure mode in that sense was a short circuit (presumably through the silicone?) because the top side connects of the die weren't thick enough.  At least that's the explanation given.  The DC tests however I am still trying to understand.  What little explanation I have managed to get about the DC tests is that there was some connection issue to sensors onboard the IGBT die (current and temperature).

Maybe I'm freaking out about nothing ;P.  Thanks for the inputs!

[jmelson]

Maybe I'm freaking out about nothing ;P.  Thanks for the inputs!

OK, die attach can have MANY more issues than installing packaged parts onto PC boards.  Since they are doing the whole process and you are only a material provider, then you have to be able to determine if the material is performing correctly.  Since these die are exposed, there could be contamination of the die that could cause immediate or delayed failure.  Then, they are attaching wires to the die.  If the surface of the die were contaminated, the wire bonding could be affected.

This could get complicated pretty quickly.

Jon