2 Heat Sink Temperature Sensor Monitoring

As shown in option 2 of Figure 1-1, a common method of tracking critical component temperature is to capture the temperature of a heat sink contacting the device to be monitored. Mechanically the sensors in these applications can either be attached to the heat sink with an epoxy, clip, or a bolt if the package permits. The equivalent thermal circuit for this method is shown in Figure 2-1, where the R_ϴJC(top) is the thermal resistance from the junction of the processor/MCU to the top of the device.

Figure 2-1 Equivalent Thermal Circuit for Heat Sink Temperature Sensing

When using this style of temperature monitoring, the measured temperature at the sensor will lag the actual processor temperature significantly due to the relatively large thermal mass of the heat sink. This additional thermal mass can slow system response to sudden changes in component temperature and can allow for component damage. Additionally, the contact between the heat sink, sensor, and processor will eventually degrade due to breakdown of the contact adhesives from time and temperature cycling. Component temperature in these types of sensing applications can still be successfully monitored with enough due-diligence in system characterization, to provide sufficient safety margin for these extreme cases.