[clug] Effect of operating temps on life of integrated circuits

[steve jenkin]

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.

There's a good paper "Calculation of Semiconductor Failure Rates" by
William J. Vigrass that lists a bunch of failure mechanisms and models,
but no values.
[PDF's available through google]

Related pages, quick reads, apart from 1st:
<http://www.tmworld.com/article/320758-What_Causes_Semiconductor_Devices_to_Fail_.php>

<http://www.tmworld.com/article/324462-Models_Predict_Failure_Rates.php>

<http://www.tmworld.com/article/317633-Using_Models_to_Predict_Semiconductor_Failures.php>

<ttp://www.tmworld.com/article/318052-The_Effect_of_Temperature_on_Failure_Rate.php>

The "Arrhenius Equation" is commonly used as an empirical method for
estimating MTTF (lifetime) from Accelerated testing. [The proposition is
that silicon devices fail for physico-chemical reasons, so lifetimes are
determined by rates of chemical reaction.]

Arrhenius observed that rates of chemical reactions approx doubled for
each 10°C rise of temp [why milk 'goes off' quickly when left out].
Individual reactions can be described by two constants (Acceleration
Factor and 'Activation Energy').

While I've come up with pointers to the theory, I wanted some more
specific numbers to use/chuck around :-)
How much lifetime do you sacrifice by running your CPU hotter?
Inversely, how slack can you be with your server room cooling and still
expect a 5 year life?

The closest I've come is this nice little table. "TEC" ==
"Thermoelectric cooler" (peltier devices)
<http://www.rmtltd.ru/subpages/app_tips_tec_high_temp.htm>

Operating temperature, °C vs TEC Lifetime, hrs
  25	  70	   85	  125	  150	  200
9,9E+05	6,0E+04 2,7E+04	4,6E+03	1,8E+03	3,6E+02

5years ~= 45,000 hrs, or 4.5E+05.
or between 125°C and 150°C in the table above.
BTW, this piece implies MTBF is median life (50%-ile), elsewhere MTTF is
quoted at 1-std. deviation (63.2%).

Thanks in advance for any insight/help/pointers.

regards
steve


PS:
If anyone wants to waste time reading, there's a nice 'Peltier Guide':
<http://www.heatsink-guide.com/peltier.htm>

One of the 'gotchas' is their inefficiency, for every Watt moved, they
can consume  1-2 Watts. If you have a 60W CPU, you end up burning
another 120W in cooling, needing a total of 180W dissipated by the
heatsink! :-(

Another cute factoid I ran into about Fans:

Noise varies with *5th* power of fan speed.
Running fans at half-speed is much quieter :-)

Not sure about the power-draw of fans w.r.t. speed.
I'd have thought cube of speed, but that article said "square law" :-(

-- 
Steve Jenkin, Info Tech, Systems and Design Specialist.
0412 786 915 (+61 412 786 915)
PO Box 48, Kippax ACT 2615, AUSTRALIA

sjenkin at canb.auug.org.au http://members.tip.net.au/~sjenkin