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As the power level required for multi-phase regulator applications is getting higher and higher, and the available circuit board area is constantly decreasing, PCB circuit board routing design has become an important part of the regulator's thermal design. The PCB board can help dissipate most of the heat generated by the regulator, and in many cases this is the only way to dissipate heat. Well-designed traces can improve the thermal performance of the circuit board by enhancing the effective thermal conductivity around the MOSFET and IC.
On the other hand, in order to reduce costs, unnecessary wiring needs to be reduced. Therefore, in order to meet the above goals, it is necessary to estimate and adjust the PCB thermal conductivity changes around the voltage stabilizer and its impact on the thermal performance of the voltage stabilizer during the design stage.
A common thermal analysis method is to calculate the average value of the effective parallel and normal thermal conductivity of the entire circuit board based on the number, thickness and coverage percentage of copper layers and the total thickness of the circuit board, and then use the average parallel and normal thermal conductivity to calculate the thermal conductivity of the circuit board . However, this method is not suitable when local changes in the thermal conductivity of the circuit board must be considered.
Icepak is a thermal modeling software tool that can be used to study local changes in thermal conductivity in circuit boards. In addition to computational fluid dynamics (CFD) functions, the software tool also takes into account the wiring and vias of the circuit board to calculate the thermal conductivity distribution of the entire circuit board. This feature makes Icepak very suitable for the following research work.
Original design and model verification
Icepak model is created based on ECAD file in 1U server application. The trace and via information of the original circuit board are imported into the model.
In order to check the thermal conductivity distribution, the 45 degree Celsius constant temperature boundary condition can be assigned to the back of the PCB board, and the uniform heat flux boundary condition can be assigned to the top of the PCB.
High temperature represents low thermal conductivity, and low temperature represents high thermal conductivity. It can be seen from the figure that the temperature is higher in the area where there is no trace, and the temperature is lower in the area with more traces. In areas with large vias, the temperature is close to 45°C.
This shows that the thermal conductivity distribution is consistent with the trace distribution in the original design. In order to obtain the local effect of the small holes, a smaller background grid size should be used.
In this example, the background grid size is 1*1mm. Each grid contains a circuit board unit, which has its own thermal conductivity in the X, Y, and Z coordinate directions, and generally they have different values.
In this model, the power loss of regulator components and traces. These power loss values have been verified in the aforementioned tests.
1U application model, in which there is air flow above the circuit board. The ambient temperature is 25°C, and the internal air flow rate is 400LFM. Figure 2b shows the temperature of the surface and components on the circuit board. The component with higher temperature is the MOSFET in the regulator.
When comparing the simulation results of the maximum temperature of each key component group with the test results, we found that they have good consistency.
Reduce circuit board traces
The original PCB design has a relatively large trace coverage, the purpose is to increase the heat dissipation in the circuit board, thereby reducing the temperature of the voltage regulator. However, in some cases, in order to reduce costs, it is necessary to reduce the trace coverage and not to use a heat sink. Therefore, the traces will be modified, and then the verification model will be used to predict the temperature of the regulator.
The above is the introduction of PCB thermal design application using CFD modeling method. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology.
