Modal Experiment And Numerical Simulation Of PCB Assembly

With the rapid development of science and technology,the application scope of electronic devices is more and more extensive.In addition to mobile phones,computers,mobile hard disks,and other portable electronic products used in daily life,more and more electronic devices are used in all kinds of vehicles.In the process of production and use,electronic equipment will bear the high temperature,vibration,and other different environmental loads,which puts forward higher requirements for the reliability of electronic equipment,so it is vital to study the reliability of electronic equipment under different environmental loads.In this paper,the PCB assembly commonly used in vehicle electronic equipment as the research object,and the reliability of PCB assembly under different boundary conditions and different loads are explored,the research on the theory of modal experiment and numerical simulation is used to search the failure of solder joints and life prediction under random vibration load and thermal cycle load,the main research work and conclusions are as follows:Firstly,the modal experiment of PCB assembly is carried out as the effective three-dimensional finite element model set up,the hammering method is usd to carry out modal experiments on the specimens.The methods are as follows: free state,short side fixation,four corner bolt fixation.Then,ABAQUS software is used to carry out finite element modeling and modal analysis.According to the results of a modal experiment,including the finite element model of vibration mode and frequency verification,the finite element model is checked by comparing the results of the experiment and simulation,and finally,an effective three-dimensional finite element model is established,which lays the foundation for the subsequent numerical simulation analysis of PCB under random vibration load and thermal cycle load.Based on the modal test and finite element modal analysis,it is found that the first natural frequency of four corner bolt is the highest under the three boundary conditions,the first four modes are mainly z-axis positive bending perpendicular to the PCB surface,the displacement and bending in the z-axis direction are big,and there is no obvious bending deformation at the fixed boundary node constraint position.With the increase of the order,the mode shape tends to be complex and presents a bending and twisting state.Secondly,the finite element numerical simulation analysis of PCB assembly under random vibration load is carried out.The acceleration power spectrum is set according to the ground random vibration test conditions of GJB150 by the method of base excitation.By observing the 1? stress-strain response program of PCB assembly under the fixed boundary condition with four angle bolts,it is found that the dangerous solder joint is located near the long side of the PCB and far away from boundary constraints.In the process of random vibration,the distribution of stress and strain in the dangerous solder joint is uneven.It is found that the weak link is the interface between the dangerous solder joint and PCB.Steinberg model is selected to predict the vibration fatigue life of dangerous solder joints.The results of numerical simulation and life prediction provide a theoretical basis for reliability design of PCB components under random vibration.Thirdly,the finite element numerical simulation analysis of PCB assembly under thermal cycle load is carried out.Anand viscoplastic constitutive equation is selected to describe the creep characteristics of solder joints during the simulation process,and the thermal cycle temperature is selected according to the American military standard ML-STD-883 E.By observing the stress-strain response program of PCB assembly,it is found that the dangerous solder joint is located on the diagonal line near the center of the BGA package.It is found that the maximum equivalent stress and the maximum equivalent strain are located at the junction of the dangerous solder joint and the chip,but they do not occur at the same time,and the change of stress and strain presents a hysteresis state.The maximum equivalent stress at-55 is greater than that at 125? ?.The results show that the equivalent strain of solder joint has almost no change after-55?,but increases after 125?.The modified coffin Manson model is selected to predict the thermal fatigue life of dangerous solder joints.The results of numerical simulation and life prediction provide a theoretical basis for the structural design of PCB components under thermal cycling.