B-4
Computer Group Literature Center Web Site
Thermal Analysis
B
Allow the board to reach thermal equilibrium before taking measurements.
Most circuit boards will reach thermal equilibrium within 30 minutes.
After the warm up period, monitor a small number of components over
time to assure that equilibrium has been reached.
Measuring Junction Temperature
Some components have an on-chip thermal measuring device such as a
thermal diode. For instructions on measuring temperatures using the
onboard device, refer to the component manufacturer’s documentation
listed in
Appendix C, Related Documentation
.
Measuring Case Temperature
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.
Note
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.
