Study Of Fast Finite Element Theory And CAD Technology For Thermal Analysis Of Complex Electronic Devices

With the rapid development of modern electronic technologies,various complex electronic devices such as high-power vacuum electronic devices,large-scale or very large-scale integrated circuits are widely used in electronic equipments and weapons.At present,military applications such as multifunctional radars,active phased array systems,millimeter-wave equipments,space military communications,and civilian requirements such as 5G communications,cloud computing,and the Internet of Things put forward higher requirements on the performance of electronic devices,and the continuous improvement of performance will inevitably lead to serious heat dissipation problems.In the design process of high-performance electronic devices,the restriction of high power to heat dissipation has become an important consideration in the design,and the power density and its thermal effect have become a barrier to further miniaturization of high-power electronic devices.Therefore,it is particularly important to quickly and accurately perform thermal analysis on high-performance and high-power complex electronic devices,and then to better design the heat dissipation structure.However,it is difficult to use the existing numerical methods to meet the needs of complex electronic devices' thermal analysis.Therefore,it is urgent to study more accurate and efficient three-dimentional thermal analysis numerical calculation methods and CAD softwares for complex electronic devices.The research works of this dissertation are focused on the rapid finite element theory and CAD technology for thermal analysis of complex electronic devices.The main content and innovation of works can be summarized as the following five aspects.1.A three-dimensional fast finite element method for thermal analysis of arbitrary complex electronic devices is proposed.The method mainly includes the following four kinds of new techniques:(1)A general finite element numerical solution technique for the thermal contact resistance is proposed.The technique does not need to modify geometric models or introduce contact elements,which greatly improves the efficiency of solving the thermal contact resistance problems.(2)In the discretization process of the finite element weak form,the high-order hierarchical basis functions are adopted,including the second-order hierarchical scalar basis functions and the third-order hierarchical scalar basis functions,which greatly reduces the number of meshes under the same solution accuracy.(3)By utilizing the hierarchical property of hierarchical basis functions,a p-type multigrid preconditioning technique based on the second-order and third-order hierarchical basis functions is proposed,which greatly improves the efficiency of solving the finite element matrix equation.(4)A modified inexact Newton-Raphson iterative method is proposed,which greatly increases the efficiency of solving finite element nonlinear equations.2.Based on the existing finite element theory for calculating radiation exchange in closed environments,a general finite element method for calculating radiation exchange in non-closed environments is proposed.It mainly includes the following two key techniques:(1)Based on the popular Hemi-cube method,an efficient view factor solver is developed,which includes various common algorithms of computer graphics,such as ray intersection,hidden surface technique and so on.(2)An advanced finite element theory of radiation exchange for the non-closed environment is proposed and the resulting finite element matrix is symmetric and positive definite.3.A finite element-based domain decomposition fast solution technique is proposed,which can be used to solve both continuous field problems and thermal contact resistance problems.It mainly includes the following three innovations:(1)A novel transmission condition based on thermal contact resistance is introduced and the weak form of the domain decomposition finite element is derived through an interior penalty procedure.Compared with the existing domain decomposition method,the biggest advantage of the proposed domain decomposition method is that no extra unknowns are introduced and the resulting finite elment matrix will be symmetric and positive definite.(2)The solving procedure of finite element matrix equation adopts the preconditioned conjugate gradient method with a two-level preconditioner,which has a superior performance in both memory and CPU time compared with the conventional finite element method.(3)In the case of nonconformal meshes on the interface of subdomains,a construction techque of union meshes is proposed which can efficiently solve complex multi-scale problems.4.An electro-thermal-stress multi-physical co-simulation technique is proposed for the collector of microwave tubes.Firstly,Microwave Tube Simulator Suite(MTSS)is used to calculate the electrical parameters of the microwave tube,and then the electrical parameters are imported into the finite element code for thermal analysis developed by us.After processing,the heat source information is obtained and further thermal analysis is performed.Finally,the temperature field results calculated by the thermal analysis are imported into the rapid thermal stress solver TSS developed by us to calculate the thermal deformation.The TSS solver combines multiple preconditioners such as second-order hierarchical scalar basis functions,multifrontal block incomplete Choleski preconditioner and p-type multigrid preconditioner.Its calculation efficiency is better than commercial software ANSYS.5.Based on the above fast finite element related theory for thermal analysis of complex electronic devices,a three-dimensional finite element thermal analysis software TS was developed with completely independent intellectual property rights.The software contains all the proposed fast solving techniques above,and has a user-friendly interface,a high-quality mesh generator,an accurate and fast finite element solver,and a variety of post-processing calculation and display modules.The solving performance of this software is better than the widely used commercial software ANSYS and CST MPHYSICS STUDIO.At present,the software has been released in the 12 th Research Institute of China Electronics Technology Group Corporation,Institute of Electronics,Chinese Academy of Sciences,and Nanjing Sanle Group Co.LTD and has been used in the thermal analysis and thermal design of practical vacuum electronic devices.