Fair enough, but in my opinion, a blown chip on a logic board is almost
invariably down to overheating.
This is only *my* opinion, though, and based on what I see coming
through for recovery.
This is also supported by semiconductor quality today. Except for some
known cases (the last one was the problem with new flame retardant
that killed a series of Fujitsu drives several years back),
semiconductors reliability is quite predictable. However they have a
limited lifetime and that derates with the operating temperature. Rule
of thumb is half the lifetime for each 10C more. (Applies to logic and
memory. Power semiconductors are less sensitive.)
The base point seems to have shifted up in the last decades, at the
moment it possibly is around 50 years at 50C. There is also
catastrophic failure temperature at 150...200C chip temperature,
depending on technology.
Today, if a chip works for some months or years and then fails, it is
allmost allways due to temperature. Example: Run a chip at 90C (chip,
not package surface temperature), and get something like 1.9 years of
lifetime.
In addition chips have "hot spots", were the local temperature is
significantly higher than the overall chip temperature. Especially
pocessor lik structures suffer from this, which includes controller
chips on disks and chipsets.
In short, if a semiconductor fails prematurely, but after working
for some time, it was in most cases insufficiently cooled and
the failure is not a surprise at all.
Arno
