| With the rapid development of electronic packaging industry,product reliability becomes more and more important.According to the investigation,in the failure of electronic products,50% of the probability is caused by the failure of welding between components and printed circuit boards,the life of welding parts will directly affect the service life of products.For the working environment of electronic packaging products,temperature and vibration have the most significant influence on their life.The service life of railway equipment will be greatly reduced due to the vibration caused by the irregular track and the temperature change caused by the periodic on-off of equipment during the running of railway vehicles.This thesis starts with temperature and vibration,using ANSYS Icepak and ANSYS Workbench software,firstly carries out thermodynamic and thermo-structural coupling analysis of automotive printed circuit board under normal service condition,and separately studies the dynamic response of PCB under thermal cycle and random vibration loading.Finally,the fatigue life of printed circuit board under thermal cycling and random vibration loading is predicted based on relevant theories.The specific research contents are as follows:(1)Based on the theory of heat transfer and computational fluid mechanics,ANSYS Icepak software is used to predict the steady-state temperature field of circuit board.The distribution of temperature field and airflow field during the service of automotive circuit board is studied,and the influence of power consumption and layout of heating chip on its existence is explored.Based on the sequential coupling method,the thermo-structural coupling analysis of PCB was completed by taking the thermodynamic information of PCB as the input load and combining the basic knowledge of thermoelasticity and thermal stress,and the thermal stress distribution of the chip packaging structure was analyzed.(2)Under thermal cyclic loading,considering the viscoplastic properties of tin-lead based solder at high temperature,Anand unified constitutive model was used to characterize the thermal deformation of metal materials caused by temperature.The transient analysis of key parts of printed circuit board was carried out by applying temperature load according to the standard of temperature cycle test stipulated by industry standard.Based on the plastic strain parameters of the solder joint,the position of the dangerous solder joint was determined and the dynamic response law of the dangerous solder joint during the temperature cycle was studied.(3)Under the loading of random vibration,the modal analysis method is used to determine the inherent characteristics of the structure of printed circuit board for vehicles.By changing the finite element mesh number,the mesh independence of the model is explored.The rationality and accuracy of the model are verified by comparing the modal test results obtained by hammering method.Random vibration load was applied according to the national rail transit vibration and impact test standard,random vibration analysis of PCB was completed,and stress and strain distribution law of PCB was studied.The relationship between the spacing of solder joints and the maximum stress of the package structure was investigated,and the fault risk location of PCB was determined.(4)Based on the Solomon model of low cycle fatigue,the plastic strain amplitude of the concerned region was extracted to predict the fatigue life of the dangerous position under thermal cyclic loading.Using Coffin-Manson fatigue empirical formula of high cycle fatigue,Miner’s linear cumulative damage theory and Steinberg model based on Gauss distribution,the fatigue life of dangerous position under random vibration loading is predicted.Finally,the linear damage superposition method is used to calculate the total damage of each dangerous position.Based on the relationship between damage and life,the fatigue life of printed circuit board is predicted under thermal cycling and random vibration loading. |
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