An important aspect of the development trend of microelectronics is the increase in circuit density, which leads to the increase in power dissipation of the core and the increase in heat, and the temperature of electronic equipment rises rapidly, thereby causing more and more failures of electronic equipment. Due to the increased density of components and the complexity of heat transfer paths, thermal analysis and thermal design of electronic devices have become a problem that cannot be ignored. For conventional electronic equipment, numerical calculation methods are often used to study the steady-state thermal characteristics of the electronic equipment, so as to provide a basis for the thermal design of the electronic equipment. However, electronic equipment in aerospace vehicles, aerospace vehicles, some radar communication systems and military electronic systems are often subject to complex changes in environmental conditions, so electronic equipment will withstand huge changes in operating temperature. In addition to the need for steady-state thermal analysis as well as general industrial electronic equipment, these electronic devices working in complex environments must also perform numerical calculations of transient temperature fields and thermal characteristics 111. This can affect the factors that affect thermal characteristics ( Such as: component geometry, heat dissipation and distribution, thermal properties of materials, thermal control methods, boundary conditions, etc.) for qualitative, quantitative analysis and computer-aided design. The results of numerical simulation have important guiding significance for optimizing the thermal design of electronic equipment, performing fault analysis, and ensuring the performance and reliability of electronic equipment working in complex environments. The research results have broad application prospects in high-tech and defense fields. 1 The basic theorem of heat transfer A large number of heat transfer processes occurring in nature and engineering practice can be divided into three types according to their heat conduction methods: heat conduction, convection and heat radiation. As a component-level analysis, only the heat conduction inside the component and the convection heat dissipation between the outer surface of the component and the air are considered. Among them, the control equation of heat conduction is obtained by Fourier's law: 1% fund project: § equipment and equipment af 毙 c, turn House. Scattered mining and two points of marriage difference cilco leg lElectronicPublishin in i! ,. Therefore, by applying 0 milk / heat production load on the chip et chip bookmark3, it represents the transient temperature of the structure; it represents the time of the process; Q represents the heat generated by the heat source per unit volume. The convective heat transfer between the outer surface of the component and the air is used as the boundary condition of the governing equation (1), that is, the rate of change of the temperature in the direction of the normal outside the surface. The subscript w indicates the wall surface, and f indicates the fluid. a and Tf can be constants or some function that changes with time and position. 2 Finite element theory The finite element method is widely used in solving heat transfer and fluid flow equations. The element shape and density of the finite element method can be arbitrarily changed, so fewer nodes can be used to achieve a better approximation of the area. Considering that the electronic components have complex shapes, the finite element method is used to perform numerical simulation and thermal analysis on the temperature field of the electronic components. Divide the solution area into a finite number of elements, choose a suitable weighting function, discrete continuous temperature field to each node, and finally combine all the elements over the entire area to obtain a series of equilibrium equations, written in matrix form 121: + is the heat conduction matrix, is the heat capacity matrix P is the temperature load matrix T is the node temperature matrix, is the node temperature and time derivative matrix The corresponding matrix elements are: in which r is the unit containing the boundary node i / The plane domain on the class boundary condition, (6) r is the plane domain on the third class boundary of the cell containing the boundary node i. The time domain of equation (3) can be obtained by the iterative calculation of the above equation. The node temperature array can be obtained at any time. , Its typical structure is as shown. It is composed of working chip, heat conducting rod, plastic package and pin. The working chip is the core part of DP and the only heating part. In order to strengthen the heat dissipation of the chip, under the chip is a heat conducting rod with a larger thermal conductivity, generally metal copper, which can enhance the heat dissipation of the chip. Plastic packaging plays the role of fixing and protecting the chip. The pins are connected to the chip through thin metal wires. Because the wire is very thin, the heat transfer through it is very small and can be ignored. The materials of each part of a typical DP are shown in Table 1. The finite element model of the thermal conductivity coefficient thermal conductivity chip thermal rod plastic package pin 4DIP is called, so only one quarter of it is used for the meshing and solution of the finite element, as shown. Because the chips, thermal rods, and pins have a relatively regular geometric structure, the use of hexahedral elements for meshing can reduce the number of elements and speed up the calculation speed. The plastic package has a complex structure, so the tetrahedral unit is used for adaptive meshing. The mesh at the junction between the parts of the component is denser, so that more accurate calculation results can be obtained. The plastic-encapsulated grid is sparse. 8W, because the heat flux of the symmetric plane of the finite element mesh of the DIP, which is only a quarter of DP, is zero, so adiabatic boundary conditions are applied. The outer surface of the chip and the surrounding air are convection heat transfer, the temperature of the given air is 322 65IK The convection heat transfer coefficient is 542W / (m, 1. Under this condition, the steady-state temperature field distribution of DP is solved by finite element as shown . 5 Steady state analysis shows that the core temperature is the highest, reaching 368.6IK. Because the thermal conductivity of the plastic package is very small, the temperature of the plastic package is obviously distributed from high to low from the center to the edge, away from the core The temperatures at the farthest corners are close to the ambient air temperature. From the longitudinal temperature distribution in the figure, the heat dissipation effect of the heat conducting rod can be clearly seen. The thermal conductivity of the pins is large, so the temperature of each pin is evenly distributed, decreasing in sequence according to the distance from the core. The ratio of heat dissipated in the five wall surfaces is shown in the example. It can be seen from the figure that the heat dissipated from the upper and lower walls is approximately equal, with a total of nearly 40% of the heat dissipated, and the heat dissipated from the far wall is the least, only 6%. The side and the pins dissipate most of the heat. It can be seen that strengthening the heat dissipation in the direction of the pins and the side will be more effective in reducing the temperature of the component. Measures that can be taken include selecting pin materials with greater thermal conductivity and changing the shape and size of the heat conducting rod to strengthen the lateral heat transfer of the component. Choose another common material for the plastic package and the pin separately, and get four different material combinations | 41. Recalculate under the same heating power and boundary conditions to obtain the maximum temperature and thermal resistance of the component as shown in Table 2. It can be seen from Table 2 that the use of materials with better thermal conductivity has a more obvious effect on reducing the hot spot temperature of the component. The internal thermal resistance of the component changes greatly as the material changes, while the external thermal resistance of the component remains almost unchanged. It can be seen from Table 2 that the heat dissipation ratio of each part of the surface of the plastic DIP is improved. Table 2 The maximum temperature of the components under different package and pin combinations A package B pin X pin Y package and pin combination maximum temperature K external thermal resistance / (KW /-') The internal thermal resistance / (KW /-') thermal conductivity of the package can significantly reduce the temperature of the component lectrnic Huse. Under the condition that the core heating power is 02W, 04W, 06W in order, change the convection heat transfer coefficient between the core surface and the air The order is 40302010W / (m, K), and the change of the maximum temperature of the core and the change of the internal and external thermal resistance are obtained as shown in and. It can be seen from the figure that the temperature of the DP hot spot changes linearly with the increase of the heating power. The smaller the convection heat transfer coefficient, the greater the external thermal resistance and the higher the hot spot temperature of the component. The change of the convective heat transfer coefficient has almost no effect on the internal thermal resistance of the component, which is determined by the material of the component. The external thermal resistance of the element increases sharply as the convection heat transfer coefficient decreases. It can be seen that when the convection heat transfer coefficient is very small, the external thermal resistance of the element is much larger than its internal thermal resistance. Therefore, in this case, to improve the heat dissipation of the component, it is almost ineffective to replace the component material to reduce the internal thermal resistance. At this time, the convection heat transfer coefficient should be large, so as to quickly reduce the external thermal resistance of the component and achieve the reduction. The purpose of the hot spot temperature of the component. In the case where the convective heat transfer coefficient has been large, the change of the external thermal resistance with the convective heat transfer coefficient has been very small. At this time, the improvement of the heat dissipation of the component can only be achieved by changing the material of the component and reducing the internal thermal resistance. Achieved the goal. 6 Transient analysis In the working process of electronic components, the power or boundary conditions of the components are not always constant, but will change with the change of the working status of the components. In the thermal design and testing of electronic components, in order to ensure the normal operation of the component, the most effective method is to work on the component in the worst working state (that is, the component has the highest heating power, the highest ambient temperature and the smallest heat exchange coefficient with the surrounding). Perform steady-state thermal analysis. However, electronic components do not always work in the worst state, especially when the worst working state of some components is very short, only a small part of their working time, this design idea will cause unnecessary waste . In addition, due to the short test time for electronic components, the components are required to have faster thermal response performance. Knowing the temperature-time response curve of the component in advance is very important for designing the cooling system of the test process. The most effective way to obtain the thermal response performance of a component is to actually measure the component to obtain data, but there is no prototype of the component in the initial design stage of the component. Transient thermal analysis of the component can provide a reasonable thermal response performance of the component Prediction. DIP temperature-time response curve under 8W pulse load. This is a typical test in the design process of electronic components, the purpose is to cause the temperature rise of the component in a short time to test the thermal stress | 51. Among them, the curve AX represents the material of the package and pin of DP uses AX in Table 2 Combination, curve BY represents the BY combination in Table 2. It can be seen from the sum that in the heat dissipation process of the component after the impulse load is applied, the curve BY is gentler than the curve AX, so the use of materials with better thermal conductivity can improve the thermal response performance of the component. Transient thermal analysis of electronic components can easily obtain the temperature change curve of any position of the component at any time. Shown is that the DP with a chip power of 08W has an ambient temperature of 50 degrees, and the convection heat transfer coefficients are these five: the temperature ei time curve of the position within the initial working period. During the use of electronic equipment, the boundary conditions are often The heat transfer process that affects the temperature of the component with time changes is a continuous changing process. Especially for avionics, this change is particularly noticeable. Taking the X-type electronic pod as an example, since the electronic pod adopts an independent reverse-pressurized back-cooled open type environmental control system driven by ram air, the temperature of the outlet air-conditioning of the environmental control system is dependent on the flight altitude and speed (ie. With the inlet temperature of the ram air). Many work phases with high thermal loads have short durations. If the thermal design of electronic components is carried out in the most serious state, the economy is not good and it is not conducive to improving the performance of the system. Therefore, it is necessary to perform transient analysis. 0 means the transient temperature of the X-type electronic pod (turn down page 28). 1134 power supply is installed on multiple primary radars. This proves that the radar's "three navigation tube processing power supply, its external size WXHXD = 71.12" design has achieved the expected results. mmX3103mmX220mm, weight about 2 Conclusion The miniaturized single-pulse secondary radar is currently in mass production and has become: Guo Yuexia (1965-) female, Henan, senior engineer, mainly engaged in the overall work of radar structure. (Continued from page 25) Degree chart | 31, where 0 ~ 10 minutes is the acceleration and climb phase of the aircraft, 10 ~ 13 minutes is the constant speed level flight phase, 13 ~ 15 minutes is the deceleration climb phase, 15 ~ 25 minutes is the constant speed In the cruise level flight phase, 25-30 minutes is the acceleration dive phase, 30-35 minutes is the deceleration climb phase, 35-45 minutes is the constant speed level flight phase, 45-50 minutes is the deceleration and descent phase. Among them, the acceleration dive stage between 25 and 30 minutes is the most severe stage of the thermal load of the pod. It can be seen from the figure that there is a temperature difference of nearly 30 degrees between the ground and the high-altitude air, which has a significant impact on the working state of electronic equipment. The change curve of temperature with time at different locations is shown in 1. Comparing 0 and 1, it can be seen that although the temperature of the nacelle drops significantly during the climb of the aircraft, the temperature of the DP rises rapidly due to the heat of the chip. When the heat of the chip and the heat dissipation of the DP surface maintain a dynamic balance, the entire component The temperature trend is consistent with the change of the surrounding air temperature, maintaining a relatively stable state, which also shows that the component has better thermal response performance. 7 Conclusion Airborne electronic equipment can withstand the complex changes in environmental conditions, so it is necessary to conduct steady-state and transient thermal analysis of electronic equipment to understand the main factors affecting the thermal characteristics of electronic components, and to grasp the direction of improvement and optimization of thermal design. Taking the dual in-line component DP as an example, the steady-state thermal analysis using finite elements shows that the internal thermal resistance of the component is closely related to the heat transfer performance of the material. Improving the thermal conductivity of the plastic package can greatly reduce the temperature of the component; the external thermal resistance of the component mainly depends on Due to the typical test procedure of the convection heat transfer coefficient between its surface and the surrounding environment, the temperature-time response curve of DP during the test process is obtained, which provides a transient temperature curve of a reasonable time period for the design of the cooling system of the test process. Provides data for thermal stress analysis of components. Transient thermal analysis in combination with the X-type pod indicates that the temperature of the component remains relatively stable throughout the rest of the time except for the rapid increase in temperature at the initial stage of the work, and is consistent with the temperature change of the surrounding air, which is optimized for the component The thermal design provides theoretical support. Guangzhou Yunge Tianhong Electronic Technology Co., Ltd , https://www.e-cigarettesfactory.com