PCB News - Two good ways to check PCB thermal design

Briefly describe two good methods for testing PCB thermal design
1. Inspection method of PCB thermal design: thermocouple;
The practical application of thermoelectric phenomenon is of course the use of thermocouples to measure temperature. The complex relationship between electron energy and scattering makes the thermoelectric potentials of different metals different from each other. Since the thermocouple is such a device, the difference in thermoelectric potential between its two electrodes is an indication of the temperature difference between the hot and cold ends of the thermocouple. If the thermoelectric potential of all metals and alloys are different, it is impossible to use Thermocouple to measure temperature. This potential difference is called the Scebeek effect. For a pair of conductors A and B of different materials, one junction is maintained at temperature T1, and the two free ends are maintained at a lower temperature To. The contact point and the free end are both located in an area of uniform temperature, and both conductors experience the same temperature gradient. In order to be able to measure the thermoelectric potential difference between the free ends A and B, a pair of conductors C of the same material are respectively connected to the conductors A and B at the temperature to and connected to a detector with a temperature of T1. Obviously, the Seebeck effect is by no means a phenomenon at the connection point, but a phenomenon related to the temperature gradient. In order to correctly understand the performance of thermocouples, this point cannot be overemphasized.

The application range of thermocouple temperature measurement is very wide, and the problems encountered are also various. Therefore, this chapter can only cover some important aspects of thermocouple temperature measurement. Thermocouple is still one of the main methods of temperature measurement in many industries, especially in steelmaking and petrochemical industries. However, with the advancement of electronics, resistance thermometers have become more and more widely used in industry, and thermocouples are no longer the only and most important industrial thermometers.
Compared with the thermocouple (resistance measurement and thermoelectric potential measurement), the advantage of resistance thermometer is the fundamental difference in the working principle of the two components. The resistance thermometer indicates the temperature of the area where the resistance element is located, and it has nothing to do with the lead and the temperature gradient along the lead. However, the thermocouple measures the temperature difference between the cold end and the hot end by measuring the potential difference between the two electrodes of the cold end. For an ideal thermocouple, the potential difference is only related to the temperature difference between the two ends. However, for an actual thermocouple, a certain non-uniformity of the thermocouple wire at the temperature gradient will also cause a change in the potential difference, which is still a factor that limits the accuracy of the thermocouple.

2, PCB thermal design inspection method: temperature rise test;
As for the thermal design, we must actually verify it in the follow-up work to make sure that the operating temperature of each chip is within the normal range. Generally, chips and components with relatively large heat generation are selected to test its maximum load working temperature, that is, to see the working temperature condition when full load for a long time. Before the test, the designer determines the chips and components with a large amount of heat. In addition, the highest temperature point of the chip is also required to be provided. Thermocouple wire is used for temperature measurement. The wire length is generally about 2m. Place the connection point of the wire head at the position to be measured and fix it with tape (the tape must be high temperature resistant and high viscosity to ensure that the high temperature does not separate and the temperature Accuracy of measurement data). At the same time, pay attention to the line not to be folded, otherwise it will affect the test accuracy.

The above is the introduction of two good methods to check PCB thermal design. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology