Motorola PrPMC800/800ET Processor PMC Module User Manual

Some components have an on-chip thermal measuring device such as a thermal diode. For 
instructions on measuring temperatures using the on-board device, refer to the 
PrPMC800/800ET Programmer’s Reference Guide and to the component manufacturer’s 
documentation listed in 

Measure the case temperature at the center of the top of the component. Make sure there is 
good thermal contact between the thermocouple junction and the component. We recommend 
you use a thermally conductive adhesive such as Loctite 384.

If components are covered by mechanical parts such as heatsinks, you will need to machine 
these parts to route the thermocouple wire. Make sure that the thermocouple junction contacts 
only the electrical component. Also make sure that heatsinks lay flat on electrical components. 
The following figure shows one method of machining a heatsink base to provide a thermocouple 
routing path.

Machining a heatsink base reduces the contact area between the heatsink and 
the electrical component. You can partially compensate for this effect by filling 
the machined areas with thermal grease. The grease should not contact the 
thermocouple junction.

Measure local component ambient temperature by placing the thermocouple downstream of 
the component. This method is conservative since it includes heating of the air by the 
component. The following figure illustrates one method of mounting the thermocouple.

Thermocouple 
junction

PWB

Tape thermocouple wire to 
top of component

Air flow