In article , DoN. Nichols says...

The thermal expansion/contraction of repeated on-off cycles, tending to
make something "crack", coupled with the fact that chemical reactions
take place faster at higher temperatures, would make me think that lower
temperatures would make for longer life.

In particular, there are existing cracks in chips resulting from
the dicing process (breaking apart the silicon wafer into all the
individual chips).

Another issue is that the die are typically wire-bonded to the
head it is on. The bonding wires are relatively fragile and
the bond between the die metalization and the wire itself is
a source of failure. Again this is exacerbated by thermal
cycling issues.

When I wire bond stuff, I use a puff of gas from a hand-held
gun to apply force to the bonds. Any ones that are weak will
detach at this point and ones that pass this test will not
fail under repeated thermal cycling.

Many commercial ICs have the bonds encapsulated - but the combination
of Si die, aluminum wire, and polymer goop never have exactly the
same thermal expansion.

Jim

Jim


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