Analysis of system temperature monitoring method

For many system designs, it is necessary to monitor high-power components (processors, field programmable gate arrays, field effect transistors) to ensure system and user safety. The nature of temperature readings is very important because it allows designers to improve performance while staying within safe limits, or to reduce system costs by avoiding over-designing elsewhere. Texas Instruments (TI)'s compact high-precision temperature sensor product line can be placed closer to these key components to achieve measurements.
How to monitor the circuit board temperature
Temperature problems in the circuit can affect system performance and damage expensive components. By measuring the temperature of areas on the printed circuit board (PCB) where there are hot spots or high power consumption integrated circuits (ICs), it is helpful to identify thermal problems and take preventive or corrective measures in time.
You may want to monitor the die temperature of high-power-consuming ICs (such as central processing units, dedicated ICs, field programmable gate arrays, or digital signal processors) to dynamically adjust their performance, or you may want to monitor hot spots around the power stage in order to Control the fan speed in the system or initiate a safety system shutdown procedure. The ultimate goal is to optimize performance and protect expensive equipment.
Heat transfer from PCB to temperature sensor
Local temperature sensors measure their own die temperature to determine the temperature in a specific area. Therefore, it is important to understand the main temperature conduction path between the die and the object or environment around the sensor. There are two main ways to conduct heat: through the die attach pad (DAP) connected to the package or through the package lead pins. DAP (if present) provides the main thermal path between the PCB and the die.

Package with DAP
If the package type does not include DAP, the leads and pins provide the main heat conduction path.

Package without DAP
Molding compound provides additional heat conduction paths, but due to its low thermal conductivity, any heat transfer through the molding compound itself is slower than heat transfer through leads or DAP.
thermal response
The package type determines the response speed of the temperature sensor to temperature changes. The figure below shows the relative thermal response rate of different types of selected surface mount technology package types for temperature measurement.

Packages without molding compound (chip scale package, die-size ball grid array package) and packages with DAP (quad flat no-lead [QFN] package, double-sided flat no-lead [DFN] package) are designed for The PCB is designed for applications with fast heat transfer, while the package without DAP is designed for applications that require a slower response rate. The fast thermal response rate enables the temperature sensor to respond quickly to any temperature changes, thereby providing accurate readings.
Design Guidelines-Bottom Installation
The sensor position should be as close as possible to the heat source to be monitored. Avoid perforations or cuts on the PCB between the heating IC and the temperature sensor, as this may slow down or prevent the thermal response. If possible, install the temperature monitor on the bottom of the PCB directly below the heat source.

The sensor is installed on the other side of the heat source
TI recommends using vias to quickly transfer heat from one side of the PCB to the other side, because vias have better copper thermal conductivity than FR-4. You can use as many parallel vias or filled conductive vias as possible to transfer heat from the heat source to the temperature monitor in order to achieve rapid thermal balance between the two ICs. A QFN or DFN package with DAP helps to further shorten the thermal resistance path between the via and the sensor die.
Design Guidelines — Stratum Considerations
If it is impractical or uneconomical to place the temperature sensor on the other side of the heat source, place it on the same side as close to the heat source as possible.
Common formation helps to achieve thermal balance

An effective way to establish a thermal balance between the heat source and the temperature monitor is to use the formation. A solid ground that extends from the heat source to the temperature sensor should be used.
  in conclusion
In the PCB design with thermoelectric area or high power consumption IC, temperature monitoring is very important. It must be evaluated whether the selection of the local temperature sensor complies with the system requirements and protection schemes of the relevant design.
The sensor location and high thermal conductivity path should be considered to establish a rapid thermal balance between the sensor and the heating element.