[clug] Effect of operating temps on life of integrated circuits
David Tulloh
david at tulloh.id.au
Sun Jan 24 01:26:58 MST 2010
steve jenkin wrote:
> I've been trying to track down any estimates/rules-of-thumb about the
> effect of increased junction temperature on expected lifetime of IC's
> like CPU's and RAM - and was hoping the Collective Wisdom of CLUG (and
> some better Google-Fu than mine) could come up with quotable figures.
>
This is real dark art stuff. Having spent (literally) months working
with a team trying to diagnose an IC failure it's not easy to figure out
(we never really did). There's a lot of stuff that could go wrong here
and it's not predictable unless you work in the area (by which I mean
being an Intel IC guy).
As the articles said, temperature basically increases the rate of
chemical reactions. Temperature cycling induces physical stress based
on things moving with the heat.
Chemical reactions that could occur that I am aware of are bond
migrations and silicon whiskers.
Whiskers are the big threat from the new ROHS (no lead) mandates,
essentially a thin whisker grows out from the joint causing a short if
it hits another joint.
The bond migrations occur at the joins of the silicon and the outside
world. I think they cold weld the copper wires onto the silicon pads,
if this is done too strongly the copper migrates into the silicon and
the pad can rip off, too little and the copper wires get too thin and
break. The migration speed would be affected by temperature, the
ripping off by temperature cycling.
You probably get migrations across PN junctions with temperature, which
is what I think you were initially referring too. That seems possible
but most of the IC failures that I'm aware of came from the
manufacturing of the package rather than breakdowns within the silicon
itself.
My advice. Forget about trying to determine your failure rate from the
mechanisms of failure. There's too many and you won't get enough
information to properly determine the failure rate. Rather just get
figures of the failure rates of CPUs in general and assume they roughly
hold. Overclockers forums could give anecdotal information.
David
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