On Fri, 03 Sep 2010 09:27:56 -0700, Jeff Liebermann
wrote:

http://www.intel.com/design/packtech/packbook.htm
for Intel's packaging handbook. Also see 14.10 section for a little
on thermal performance. There's a section on thermal package stress
at:
http://www.intel.com/Assets/PDF/pkginfo/ch_04.pdf
See section 4.2.1 under "Stresses generated during a thermal
excursion".

I just noticed table 4-14 on Page 4-24 of the above handbook. It's a
table of the number of power cycles a CPU is expected to endure before
failure.

4.2.2 Temperature Cycles in Operation
A microprocessor package is subjected to numerous heating and
cooling cycles in operation. When the device is powered up, its
temperature rises, and when it is shut down, its temperature drops.
The magnitude of the maximum temperature on the die surface depends
on the thermal solution employed, and is usually between 80 to
125°C. In addition to these power on and power off cycles
(maxi-cycles), the microprocessor is cycled between different
intermediate temperature values depending upon processor usage
(mini-cycles) in any application program. The Institute for
Interconnecting and Packaging Electronic Circuits [2] lists the
typical worst case usage conditions for personal computers and
consumer electronics as given below. This table is intended only as
a guideline, and individual companies use different field use
conditions based on their research.

Category Worst case use environment
Tmin °C Tmax °C DT °C Dwell (hrs) Cycle/yr Approx. Years in Service
Consumer 0 +60 35 12 365 1-3
Computers +15 +60 20 2 1460 5

As I read this, if you turn your computer on and off once a day for 5
years, the CPU could fail due to thermal fatigue. For consumer
electronics, it's 1-3 year. Lovely...




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Jeff Liebermann
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Santa Cruz CA 95060 http://802.11junk.com
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