Operating temperature of Integrated circuits

Hi,
The UCC3817A PFC controller IC has an operating temperature range of 0-70degc.
However, its junction temperature is said to be rated to 150degc

Do you know what would happen if it was operated at say 100degc for 8 hours per day for 30 years?

UCC3817A
https://www.ti.com/lit/ds/symlink/u...l-digikeymode-df-pf-null-wwe&ts=1593441712447

Ther is, or was, a UCC1817 which would have been rated and
qualified to -55C - 125C. MIL qualification would have aimed
at 125C for 10 years. This "ought to" make 100C / 30 years OK
as lifetime is said to halve every 10 degC. However this is more
"rule of thumb" (depending on physics of failure, activation
energies and dominant mechanisms) than a hard fact.

Still if you can find the 1817A part and its reliability information
(which TI is pretty good about making available) you can get
some feel for the deal.

There's rated temp for reliability and there's temp-range
conditions for the electrical performance tables. "Back in
the day" companies like TI would design for the most
extreme temperature, and then tighten the "commercial
grade" parts' spec table to what was manufacturable
given that test temp range (likely binning out the best, for
the higher-margin industrial and MIL part grades). Anyway,
performance spec table basis and reliability (abs max)
table basis are separate things.