introduction Avionics equipment is inevitably subjected to vibration and shock during production, transportation and use. The effects of these vibrations and shocks may lead to various forms of failure or even destruction of electronic equipment. The damage of electronic equipment caused by these vibrations and shocks loosens the screws and nuts, the deformation of the chassis, the cracking and peeling of PCB solder joints, and the breakage of device pins. Especially as PCBs continue to develop in the direction of high precision, high density, small pitch, multilayer, high-speed transmission and the rapid development of large-scale integrated circuits (VLSI), it has more complete functions, smaller size, and more packaged pins More and denser ICs and SOICs continue to emerge, especially the widespread application of surface mount technology (SMT), which poses higher challenges for PCB components. For avionics, faults caused by vibration and shock will greatly reduce their reliability and have extremely serious consequences. Relevant literature shows that the failure rate of avionics products caused by vibration and shock dynamics accounts for 28.7% of the total failure rate. In the vibration environment test of avionics, PCB also often occurs. The dynamic analysis and design of PCB components can effectively reduce the probability of failure in environmental tests and improve the reliability and quality of avionics products. Kinetic analysis is based on analysis of dynamic characteristics. The dynamic model of PCB components can be established by analyzing their dynamic characteristics. Only when an accurate dynamic model is established can effective dynamic analysis be carried out. To this end, this paper attempts to use the pre-test analysis technology combining finite element analysis (FEA) and experimental modal analysis (EMA) to analyze the dynamic characteristics of a avionics PCB assembly (shown in Figure 1), and establishes the Finite element dynamic analysis model of PCB components. 1 Finite element modal analysis As a mature numerical analysis technology, finite element analysis technology (FEA) is widely used in the analysis of the dynamic characteristics of electronic equipment PCB components. In addition, FEA can help engineers design more reliable PCB components and predict potential failure and fatigue from the beginning of the design. This article takes the PCB assembly of an avionics device (Figure 1) as the research object, and its external dimensions (length & width; width & thickness) are 133.5 mm & TImes; 79 mm & TImes; 1.8 mm, which are fixed to the electronic equipment by screws at four corners of the PCB On the chassis. The external dimensions and fixing methods of the PCB assembly are similar to the specified standard test PCB, but the thickness is larger. Components and connectors are assembled with PCB using surface mount technology (SMT), and the packaging of components is mainly BGA, QFP and SOP. Figure 1 Object PCB assembly 1.1 Finite element analysis model The physical property parameters of the materials that make up the PCB components of the object are shown in Table 1. Based on the information of the geometric dimensions of the PCB assembly and related material information, a finite element analysis model was established in ANSYS (Figure 2). Because what you want to get is the dynamic performance data of the PCB assembly as a whole, not the detailed data of the components themselves, so when building the model, the components and connectors are simplified. Specifically, rectangular and square blocks are used to simulate the components, and the connectors are simulated using their rough outlines. Each part of the finite element analysis model uses three-dimensional solid elements (SOLID187) for meshing (using solid elements for meshing, although the calculation amount is increased to a certain extent, but the workload from the CAD to CAE model is greatly Reduce, is conducive to the promotion of engineering applications), and the connection between components and PCB, connector and PCB are simulated using multi-point constraint (MPC). At the same time, because the rigidity of the electronic chassis is much greater than the rigidity of the PCB assembly, fixed support constraints are imposed on the screw holes at the four corners in the finite element model to simulate the screw connection between the PCB assembly and the device chassis. Table 1 Physical parameters of the materials of each component of the target PCB Figure 2 The finite element model of the object PCB assembly 1.2 Finite element modal analysis results The finite element model of the target PCB assembly is established, and the Block Lanczos Method is used for modal analysis. Modal analysis is to solve the characteristic equations of the system. Generally, the characteristic equations of a multi-degree-of-freedom system can be in the form shown in equation (1) to obtain the eigenvalues ​​and eigenvectors of the system, that is, the natural frequency and mode of the vibration system. In the formula, [M]-the mass matrix of the system, assembled from the element mass matrix in the finite element modal analysis; [K]-the stiffness matrix of the system, assembled from the element stiffness matrix in the finite element modal analysis; X} —the displacement vector of the system; ω—the eigenvalue of the system. Through modal analysis, the first three natural frequencies and vibration modes of the target PCB assembly fixed with four screws are obtained, as shown in Table 2. The first-order mode of the PCB assembly is first-order bending, the second-order mode is torsion, and the third-order mode is sinusoidal. These vibration modes are similar to the JEDEC standard board fixed with four screws. Table 2 Finite element modal analysis results Figure 3 PCB assembly first-order mode (FEA) Figure 4 2nd order vibration mode (FEA) of PCB assembly Figure 5 PCB assembly third-order mode (FEA) Motion Control Sensor is an original part that converts the change of non-electricity (such as speed, pressure) into electric quantity. According to the converted non-electricity, it can be divided into pressure sensor, speed sensor, temperature sensor, etc. It is a measurement, control instrument and Parts and accessories of equipment. Encoder And Decoder,Encoder For Motor , Encoder In Communication,Encoder Communication Changchun Guangxing Sensing Technology Co.LTD , https://www.gx-encoder.com
