recently, ee times ran a piece called, “make accurate temperature measurements using semiconductor junctions”. the ee times piece does a good job of describing how to measure junction temperature using diodes and the calculations necessary to convert those readings into useful temperature measurements.
at coolingzone, we’ve run a four part series by dr. bruce guerin entitled, “determining the junction temperature in a plastic semiconductor package” that is a good companion article to the from ee times. in this series, dr. guerin takes you through the steps to determining junction temperature. read about determining the junction temperature in a plastic semiconductor package part 1, part 2, part 3 and part 4.
finally, a word of caution for the sytem level thermal engineer with regards to junction temperature, beware the designer who uses theta-ja for predicting the absolute value of the junction temperature in their particular design! according to jedec, “the intent of theta-ja measurements is solely for a thermal performance comparison of one package to another in a standardized environment. this methodology is not meant to and will not predict the performance of a package in an application-specific environment." read about theta-ja [junction temperature] cautions.
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