[s-cars] POS failure analysis

[Richard Tanimura]

My car doesn't have the POS component so I am not affected either way. But I
have enormous respect for those people who really dig in and give us hard
facts. This is a salute to you and the others on this list that do this.

Rich

-----Original Message-----
From: s-car-list-bounces at audifans.com
[mailto:s-car-list-bounces at audifans.com]On Behalf Of Mike Sylvester
Sent: den 11 mars 2004 20:02
To: s-car-list at audifans.com
Subject: [s-cars] POS failure analysis


A colleague and I performed a failure analysis on my failed POS.

1st we did some non-destructive testing.
x-ray didn't reveal anything except mildly interesting photo.
The curve tracer confirmed that ports 1 and 3 were OK and port 2 was open
circuit.

The part was then opened up.

Inside are 3 FETs or IGBTs potted in some very soft clear material, almost
liquid.

The dies look OK, so the failure is not from an overheating condition.

Under magnification we found that a bond wire failed where it connects to
the output terminal.

This failure is most likely from thermal shock  ( Rapid temperature change)
or fatigue.

As someone else had mentioned, hitting this part with water when washing
your engine could rapidly cool the part.


This finding does not totally discount the theory of poor heat dissipation.

It is possible that the bond wire joint was marginal from the factory, but
if the heat dissipation was poor due to lack
of thermal paste the internal temperature extremes may have fatigued the
bond wire joint over time.


I am curious if this is the common failure.  If anyone has a bad POS that
they would be willing to give up, I could take a look at it.

Mike Sylvester

P.S.

This weekend I will post the photos of the FA to my website.
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