Junction temperature estimation
Junction temperature estimation
(OP)
If you dont have any thermal information on a chip and need to estimate the temperature of the junction, how would you do this? Also, I dont have any dimensions of the die or any internal chip info. What I have been doing is estimating a combined thermal conductivity representing the chip and calculation a maximum temperature using a CFD program. Then I use the thermal resistance if I have it available. If not, I use thermal resistances of similar packages to estimate junction. Anyone know of a better way?
thermdes
thermdes





RE: Junction temperature estimation
If not, try harder to get the data from the manufacturer -- you may have to get your VP to call their VP. Or my preference, if possible, is to get a sample and cut it in half.
ko (www.ecooling.biz)
RE: Junction temperature estimation
RE: Junction temperature estimation
TTFN
RE: Junction temperature estimation
RE: Junction temperature estimation
To be fair, die and package construction details are proprietary and the trend is slowly going in the right direction: more manufacturers are now providing j-b and some even provide compact models.
ko (www.ecooling.biz)
RE: Junction temperature estimation
TTFN
RE: Junction temperature estimation
For all other cases, you need more data. The thermal path to the circuit board is very application-specific, anywhere from 5 to 95% of the heat can take that path.
That reminds my of another way to estimate j-b:
If the supplier's test setup is defined, including pcb copper content, you can model their test and vary j-b until your model matches the j-a test data.
btw, what's an OP?
ko (www.ecooling.biz)
RE: Junction temperature estimation
TTFN
RE: Junction temperature estimation
thermdes
RE: Junction temperature estimation
TTFN
RE: Junction temperature estimation
RE: Junction temperature estimation
Typically, we ahve a -30ºC to +50ºC temperature range of usage with nary a iota of data on actual temperatures and actual usage and actual duty cycles. That results in something like a 104range on lifetime. A 10ºC error in junction temperature in your model would harly make a dent.
TTFN
RE: Junction temperature estimation
A better way to make design decisions is to keep all dice below their maximum operating temperature when your product is operating in it's specified worst-case environment.
Thermdes, there are a wealth of papers on using CFD to model IC packages. Browse through these sites
http:
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Still, the bottom line is if you don't know the internal construction of a package and do not have a detailed or DELPHI model, then you cannot "accurately estimate junction temperature". Even if you have Flopack, you must either enter the precise details or use estimates based on similar packages...
When you need more accuracy, the only choices I'm aware of are what I already mentioned, all of which have their own set of pitfalls.
1. Get the details from the supplier
2. Take the package apart
3. If the supplier has j-a test data, simulate the supplier's test and adjust your package model to match their test at several points
ko (www.ecooling.biz)