Introduction of Two Common Test Methods for PCB Thermal Design

Last Update Time: 2018-12-28 10:26:41

In addition to useful work, most of the electrical energy consumed by electronic equipment during operation is converted into heat. The heat generated by the electronic device causes the internal temperature to rise rapidly. If the heat is not dissipated in time, the device will continue to heat up, and the device will fail due to overheating, and the reliability of the electronic device will decrease. SMT increases the installation density of electronic equipment, reduces the effective heat dissipation area, and seriously affects the reliability of equipment. Therefore, research on thermal design is very important. In this article we will introduce two usual testing methods for PCB thermal design.

Method one: Thermocouple

The practical application of the thermoelectric phenomenon is of course to measure the temperature using a thermocouple. The complex relationship between electron energy and scattering makes the thermoelectric potentials of different metals different from each other. Since a thermocouple is such a device, the difference in thermoelectric potential between the two electrodes is an indication of the temperature difference between the hot and cold ends of the thermocouple. If the thermoelectric potentials of all metals and alloys are different, it is impossible to use. A thermocouple is used to measure the temperature. This potential difference is called the Scebeek effect. A pair of conductors A and B of different materials maintain one contact at temperature T1 and the two free ends at a lower temperature To. Both the junction and the free end are located in a uniformly temperature region, and both conductors are subjected to 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 connected to conductors A and B at temperature to, respectively, to a detector of temperature T1. It is quite obvious that the Seebeck effect is by no means a phenomenon at the junction, but a phenomenon related to the temperature gradient. In order to properly understand the performance of the thermocouple, this cannot be overemphasized.
Thermocouple temperature measurement is used in a wide range of applications, and the problems encountered are diverse. Therefore, this chapter can only deal with several important aspects of thermocouple temperature measurement. Thermocouples are still one of the main means of temperature measurement in many industries, especially in the steel 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 most important industrial thermometers.
Resistance thermometers and thermocouples (compared to resistance measurements and thermoelectric measurements) have the advantage of fundamental differences in the operating principle of the two components. The resistance thermometer indicates the temperature of the area in which the resistive element is located, independent of 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 at 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, some non-uniformity of the galvanic filament at the temperature gradient also causes a change in the potential difference, which is still a factor limiting the accuracy of the thermocouple.


Methodd two:Temperature rise test
 For thermal design, we must actually verify in the subsequent work to determine that the operating temperature of each chip is within the normal range.

Generally, chips and components with relatively large heat are selected to test the operating temperature of the maximum load, that is, the operating temperature condition when the vehicle is fully loaded for a long time. The chip and components that generate a large amount of heat are determined by the designer before the test, and the highest temperature point of the chip is also required (the highest temperature point can be determined by an infrared thermal phase detector).

The temperature measurement uses thermocouple wire. The wire length is generally about 2m. Place the connection point of the wire at the position to be measured and fix it with tape. The tape must be high temperature resistant and highly viscous to ensure high temperature and no temperature. The accuracy of the measured data). At the same time, it should be noted that the line cannot be folded, otherwise it will affect the test accuracy.


This article is from Allicdata Electronics Limited. Reprinted need to indicate the source.