source:power adapter Popular:adapter release time:2021-04-21 09:52:20 Article author:sznbone
The early industrial standards for heat transfer of power adapters were mainly SEMI standards, which defined the test standards for IC packaging in natural convection, wind tunnel, and infinite flat test environments.
Since 1990, the JEDECJC51 committee has invited manufacturers and experts to formulate new industrial standards for heat transfer, and put forward a number of standards for thermal management. Compared with the SEMI standard, although the basic measurement methods and principles of the new heat transfer industry standard are the same, the content is more complete. In addition, some definitions are explained more clearly.
Two thermal resistance values are defined in the SEMI standard, namely Rja and Rjc. Among them, Rja measures the heat transfer from the chip interface to the atmosphere under natural convection or wind tunnel environments. Since the measurement is carried out under standard conditions, there are different results for different substrate designs and environmental conditions. This value can be used to qualitatively compare the ease of heat dissipation of the package. Rjc refers to the thermal resistance of heat transferred from the chip interface to the IC package shell. It is necessary to contact an isothermal surface during measurement. This value is mainly used to evaluate the performance of the heat sink.
With the change of packaging form, several measurement parameters such as Rjb, ψjt, and ψjb have been added to the new JEDEC standard. Among them, Rjb is the thermal resistance from the chip interface to the test board in an environment where almost all the heat is transferred from the chip interface to the test board. This value can be used to evaluate the heat transfer efficiency of the PCB. ψjx is a heat transfer characteristic parameter, which is defined as follows.
(1) The definitions of ψ and R are similar, but the difference is that ψ refers to the majority of heat transfer, while R refers to the entire heat transfer. When the actual electronic system dissipates heat, the heat will be transferred from the top and bottom of the package or even around it, and not necessarily in a single direction. Therefore, the definition of ψ is more in line with the measurement conditions of the actual system.
(2) ψjt refers to the thermal resistance generated when part of the heat is transferred from the chip interface to the upper shell of the package. This value can be used to predict the chip interface temperature from the external surface temperature of the IC package for actual system products.
(3) ψjb is similar to Rjb, which refers to the thermal resistance generated when part of the heat is transferred from the chip interface to the test board under the environment of natural convection and wind tunnel, which can be used to predict the junction temperature from the board temperature.
Although the various thermal resistance measurements in the standard can be applied to the temperature prediction of actual system products, there are still great limitations in actual application. When using standard Rja, Rjb, ψjt, ψjb and other measurement parameters to predict the temperature of system products, pay attention to the size of the test board, copper foil layer and copper content used in the standard test conditions, and also pay attention to the nature of the measurement. The difference between convection and wind tunnel environment and actual system.
Generally speaking, the thermal resistance or heat transfer parameters measured by experiments are mainly used to qualitatively compare the heat dissipation performance of IC packages. That is, no matter which package factory is packaged, as long as the standard method is met, the heat dissipation conditions can be compared. It is very helpful to understand the heat dissipation design or heat transfer status of the IC package. In addition, experimental measurements can also be used for verification and simplification of numerical simulations.
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