A common thermal debug and characterization technique involves the use of one or more thermocouples or thermistors placed within the system to obtain real-time temperature measurements. This approach provides valuable insight into the thermal performance and limitations of the system. However, certain precautions must be taken to ensure that the results gathered are accurate and that thermal operation is properly interpreted.
AMD does not recommend placing a thermocouple between the heatsink and the device to perform case measurements, as this practice can yield erroneous readings, compromise system performance, and, in some cases, cause damage to the device. Instead, it is suggested to first measure temperatures at multiple points on the external base and/or fins of the heatsink to assess thermal conduction to the heatsink. If there is a significant temperature variance between the SYSMON reading and the heatsink measurement, it is advisable to investigate the heatsink contact with the device and/or the heatsink construction as an initial course of action. If no issues are found in those areas and a device case measurement is still required, the best method is to drill a hole through the heatsink to the area of the device that is intended to be probed.
Ensure there is very good contact between the thermocouple and the device through the provided hole. Achieving this can be challenging, and poor contact with the device often results in erroneous readings. For this reason, along with the potential modification or damage to the thermal system required for this measurement, it is advisable to consider this method only as a last resort. In most cases, it is not necessary to diagnose thermal issues in the system. When adhering the thermocouple to the measurement point, as repeatedly emphasized, maintaining good contact with the measuring surface is essential. Improper application of thermal epoxy, such as when the thermocouple lacks direct contact with the case or when excessive epoxy is applied, can lead to several degrees of discrepancy compared to the actual surface measurement.
Using thermal tape is a more common method to attach the thermocouple to the measurement surface because it is less permanent. However, a frequent issue is maintaining adequate contact. If the tape is not taut enough or does not have a good surface to adhere to, the thermocouple can lift, resulting in reduced readings. Coupling these common issues with the inherent uncertainties of the thermocouple measurement itself can often lead to misinterpretation of results. Therefore, it is essential to address these and other potential sources of error before drawing conclusions from the data.