How To Improve The Thermal Reliability Of PCB

In many applications, the weight and physical size are very important. If the actual power consumption of the components is very small, it may lead to a high safety factor in the design, so that the circuit board design uses the component power consumption value which is not consistent with the actual or too conservative as the basis for thermal analysis.  

In general, the distribution of copper foil on PCB board is very complex, and is difficult to model accurately. Therefore, it is necessary to simplify the shape of wiring when modeling, and try to make the electronic components on the circuit board of ANSYS model which is close to the actual circuit board, such as MOS tube, integrated circuit block, etc.  

Thermal analysis

Thermal analysis during patch processing can help designers to determine the electrical performance of components on PCB board, and help designers to determine whether components or board will burn out due to high temperature. The simple thermal analysis is only to calculate the average temperature of the board, while the complex one is to establish a transient model for the electronic equipment with multiple boards. The accuracy of thermal analysis ultimately depends on the accuracy of power consumption provided by the board designers.  

In many applications, the weight and physical size are very important. If the actual power consumption of the components is very small, it may lead to a high safety factor in the design, so that the circuit board design uses the component power consumption value which is not consistent with the actual or too conservative as the basis for thermal analysis. On the contrary (and more serious), the design of thermal safety factor is too low, that is to say, the temperature of components in actual operation is higher than that predicted by the analysts. Such problems are generally need to be solved by adding heat sink or fan to cool the board. These external accessories increase the cost and prolong the manufacturing time. Adding fans to the design will also bring instability to the reliability. Therefore, the PCB board mainly adopts active rather than passive cooling methods (such as natural convection, conduction and radiation heat dissipation).  

Simplified board modeling

Before modeling, analyze the main heating devices in the board, such as MOS transistor and integrated circuit block, which convert most of the lost power into heat. Therefore, these devices should be considered in modeling.  

In addition, the copper foil coated as a lead on the circuit board substrate must also be considered. They not only play a conductive role in the design, but also play a role in conducting heat. The board with large thermal conductivity and heat transfer area is an indispensable part of electronic circuit. Its structure is composed of epoxy resin substrate and copper foil coated as a lead. The thickness of epoxy resin substrate is 4mm, and the thickness of copper foil is 0.1mm. The thermal conductivity of copper is 400W / (m ℃), while that of epoxy is only 0.276w / (m ℃). Although the added copper foil is very thin, it has a strong guiding effect on heat, so it can not be ignored in modeling.