The central topic of the power module: This article refers to the address: http:// Package options for onboard power modules Power module solution: Understanding the thermal performance of the power module from the air flow diagram Currently, distributed power architectures are widely used in communications and computing equipment, which often employ on-board power (BMP) modules to perform power conversion wherever possible as close to the point of load. Over the years, advances in devices, circuits, and packaging have made BMP modules more efficient, smaller, lighter, and thinner. These all lead to an increase in power density, which in turn poses a challenge to packaging technology. Although the open power module design has the advantages of thin thickness and light weight, there are design deficiencies in terms of thermal performance, strength and long-term reliability. In fact, although the market supports open power modules and their voices that do not require the benefits of heat sinks, there are few fair and objective data on the characteristics of different BMP packages. As a result, many BMP module users are often confused when choosing the right power module for their particular application. There are four main types of BMP packages to consider: single-board closed, double-board closed, single-board open, and dual-board open Power module. Single board enclosed and open power modules Open modules are often considered to perform better in terms of thermal performance than the same closed modules, but this is only partially correct. Factors affecting thermal performance include air flow patterns (layered or turbulent), airflow region distribution, material properties, and geometric configurations such as board spacing, device spacing, and alignment, so only a large surface area is not always Means more efficient heat transfer and better thermal performance. Modules without heat sinks were simulated using computational fluid dynamics. The air flow pattern (whether layered or turbulent) determines the thermal performance. The flow diagram is characterized by the Reynolds Number, which is defined by the rated air velocity, characteristic length, and air viscosity. For typical BMP applications, airflow can be divided into crossflow or inflow. The airflow velocity is usually measured at a distance from the PCB between the PCBs, and the board spacing is taken as the characteristic length. For cross-flow, the point of transition from lamellar to turbulent flow occurs at R~2100, which is roughly equivalent to the case where the airflow velocity is 1.25 ms-1 when the board spacing is 0.984 inches (25 mm). Air is a poor thermal conductor, so that the thermal conductivity of the edge layer of the laminar airflow in the open module is poor. In contrast, the thermal conductivity of the package around the enclosed module is about 0.25 W/mK, which is about ten times better than air, which helps to dissipate heat. Therefore, the metal shell of the closed module now functions to expand the heat transfer surface. In the 1.25~1.9ms-1 airflow transition region, more air enters between the components of the open module, thereby increasing the local heat convection conductivity and effective surface area, while the heat dissipation from the enclosed module housing The effect has not increased correspondingly. As a result, the thermal performance of open modules begins to increase at some point faster than closed modules. When the air flow rate is less than 1ms-1, the closed module has better thermal performance, and the maximum and average device temperatures are lower than the open module. The situation between the two modules is different between 1ms-1 and 2ms-1. The turning point of the performance of the two occurs at a flow rate of about 1.25 ms-1, which is the transition point of the gas flow from the laminar airflow to the turbulent flow. Open modules exhibit better performance when the flow rate exceeds 2ms-1. As this example clearly shows, the flow diagram determines the difference in thermal performance between closed and open modules. Air flow rates between devices in open modules are often overestimated at lower input airflow rates. It is found that the average air velocity between devices is less than 0.25ms-1 when the input airflow velocity is 1ms-1, which is similar to natural convection. When the input airflow is in the lamellar region, there is no evidence that the device height variation of the open module can lead to turbulence. At the same time, it is also found that the closed circuit module does not always have a much higher flow resistance than the open module. At low flow rate to medium flow rate, the difference between the two types of modules is small, only in the high flow rate range (≥3ms- 1) It only began to become apparent. Dual board module test The two-board power module test uses a half-brick module in which one core FR4 board is embedded with a core winding and the other IMS (insulated metal substrate) board is mounted with a power semiconductor device. The nominal spacing between the FR4 and IMS boards is approximately 0.2362 inches (6 mm) and the gap between the module and the test board is approximately 0.1575 inches (4 mm). At this time, the open module gets some benefits from the airflow between the FR4 and the IMS board, and its metal plate also enhances the convection at the top, where the airflow speed is the fastest. In contrast, closed modules have a smaller surface area and increase the thermal resistance of some devices, both of which result in higher temperatures for closed modules under the same thermal and electrical conditions. Conclusion In all cases, single-board open modules do not perform better than the same closed modules in terms of thermal performance, and closed modules perform even better than open modules in the case of natural convection or low air flow rates. Of course, when the air flow rate is large enough, the temperature of the single-board open module is still lower than that of the closed module. 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