Finding Case Temp
Finding Case Temp
(OP)
Sorry if this is a dumb question. I'm new and an Intern. I have some thermocouples mounted into the base of some heat sinks to get temp readings while running a stress test in my chamber. How can I find out what the case temp is of the chips? Do I just need to worry about the thermal conductivity of the thermal greese since the thermal couples are mounted in the base of the heat sink? Thanks ahead of time for any help.





RE: Finding Case Temp
RE: Finding Case Temp
RE: Finding Case Temp
If I were trying to do that I would attempt to use the absolute smallest T/C you can possibly get your hands on and then make sure it is touching the actual IC case.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Finding Case Temp
RE: Finding Case Temp
1) Use thermocouple to measure the chip in a couple of known steady state power consumption scenarios.
2) Use the thermocouple to measure the heat sink under the same thermal loads.
Now you know the difference between case and heatsink.
RE: Finding Case Temp
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Finding Case Temp
TTFN
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RE: Finding Case Temp
Other option is a thermographic camera. These are expensive but can normally resolve 0.1C or better. Depends on just how accurate you need to be - if you are running a device so close to the limit that a degree or two is the difference between survival and failure then there is a problem. That's why the heatsink temperature is normally a good enough measure.
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Sometimes I wake up Grumpy.
Other times I just let her sleep!
RE: Finding Case Temp
Sort of works.
RE: Finding Case Temp
Technically, there is another factor, PhiJ-B, that may be more appropriate to your situation. It depends on your system, i.e. system exposed to open enviornment with air movement, system in enclosure with minimal air movement / no appreciable cooling of the flowing air, circuit connected to a large ground plane (a.k.a. huge heat sink / spreader
The best method for estimating die temp is to use the method outlined by IRSTUFF. I have used that method successfully in the past, and found it be VERY accurate (ran a correlation exercise with the component manufacturer and the correlation factor was like 98%). Furthermore, it makes the most sense. You are measuring a property on the actual die that is linear over temperature. Plus you don't have to worry about the thermal lagging / smoothing effect of the case and/or PCB.
RE: Finding Case Temp
TTFN
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RE: Finding Case Temp
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Sometimes I wake up Grumpy.
Other times I just let her sleep!
RE: Finding Case Temp
RE: Finding Case Temp
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Finding Case Temp
it can make remote measurements on larger surfaces like heatsinks , and closeup case temps on single power devices without making physical contact.
to decide if something is thermally challenged, check the thermal derating of those hot devices along with the actual thermal dissipation taking place in a worst case situation.
hope this helps.
RE: Finding Case Temp
Just a thought.
Mike