Jim Levie wrote:

On Wed, 09 Feb 2005 14:39:57 -0800, Jim Stewart wrote:


I think that you've oversimplifed the situation. I don't
think you will find much difference in lifetimes between
a semiconductor running at 20 deg C and one running at
80 deg C. Not today with modern parts. As long as the
part is working with within it's current and voltage
safe operating area and within it's temperature range,
you should not expect more failures than if it were
running at 20 deg C.


As far as I know the characteristics of materials hasn't recently,
although manufacturing processes have. Modern parts are better but the
effects of temperature on material migration is solely a materials
property. Testing that I was involved in some 15 years ago showed
measureable changes in device characteristics after relatively short runs
at the upper limit for a number of devices. Extrapolating that out results
in the prediction of earlier failure as compared to the same device
running at the lower end of the temperature range.

I used to have a number of papers from other studies done on a wide
variety of devices that supports what physics says should happen.

That's not to say that the manufacture's data is wrong. Many devices have
a published lifetime vs temperature spec and on average those devices will
run according to that curve. But that wasn't the question the OP asked.

I went back and reread your post and I don't
disagree in principle. The failure rate may
indeed be exponential with temperature. The
*practical* issue is "where are we on the knee
of the curve"? If, at 80 deg c, we are still
way down on the flat part of the curve, the
temperature effects on reliability are very
small-to-nonexistant. I maintain that this
is the case with modern power semiconductors
in decent metal-and-glass packages, operated
within their specifications.

I would have no problem designing, selling, and
standing behind a warranty on a product whose
parts are operating within the manufacturer's
specifications, even if it meant running a power
semiconductor at 80 or 100 deg C, as long as
I knew that worst-case, the value would never
be exceeded.