Reliability Of Circuit Board Assembly Under Thermal Cycle And Random Vibration

With the continuous development of packaging technology,electronic devices are gradually developing towards high integration,high performance,and multi-purpose,and their packaging technology has also stepped into the era of small pitch and high density.Modern electronic devices are subjected to high-temperature shock,mechanical vibration,and coupling of various loads during actual service.Therefore,this paper addresses the reliability of PCB assemblies with different board structures and simulates three different board structures under thermal vibration loads to find the effect of changes in board structure on PCB assemblies and solder joints to provide a basis for improving board reliability.The main work is as follows.1.Modal experiments were conducted for three different PCB assemblies with different board structures at 25°C and 60°C.The three-dimensional finite element model of the PCB assembly was constructed,and modal analysis was performed using the finite element software ABAQUS.The inherent frequencies and modal vibration patterns obtained from the modal experiments and FEM analysis were compared to verify the reasonableness of the established FEM models and provide a basis for the subsequent work in this paper.Based on the results of the modal experiments and FEM modal analysis,it was found that:(1)the modal vibrations of PCB assemblies with different board structures showed that the deformation near the center of the PCB board was much more significant than that near the restraint point of the PCB board;(2)under the same temperature conditions,the inherent frequencies of 1mm open seam board(Aboard),1mm seamless board(B board)and 1.6mm seamless board(C board)with the same chip layout increase in the order of Increasing,from the inherent frequency formula can be obtained,indicating that the circuit board slotting would reduce the inherent frequency,the appropriate increase in board thickness could improve the inherent frequency;(3)by the same chip different board structure of the PCB assembly modal experimental results,the temperature increases would lead to a reduction in the inherent frequency of the circuit board assembly.2.Based on the unified viscoplasticity theory,Anand's principal structure equation,finite element numerical simulation analysis of PCB assemblies of three board structures under cyclic thermal loading was carried out.The locations of hazardous solder joints on PCB assemblies under cyclic thermal loading were found,and the general law of stress-strain and life prediction model of unstable solder joints were analyzed while their fatigue life was calculated.It was found that:(1)PCB assemblies of different board structures under cyclic thermal loading all leaded to a small warpage deformation of the BGA package block,with smaller deformation in the center of the package block and larger deformation around it;(2)the Mises stress on the hazardous solder joints on board A,board B and board C with the same layout for mounting nine chips decreases in order,and the hazardous solder joint thermal fatigue life increases in order,indicating that under cyclic thermal loading,the life of PCB components decreases with the reduction of board stiffness.3.Numerical finite element simulation analyzed of PCB assemblies of three board structures under random vibration loads was carried out.The acceleration power spectrum was set up using the base excitation method according to the land random vibration test conditions of GJB150.The locations of hazardous solder joints on PCB assemblies of different board configurations under random vibration loads were determined,and the life prediction model calculated the fatigue life of hazardous solder joints.It was found that(1)under the same vibration shock conditions,large size BGAs would be subjected to greater vibration stress than small size BGAs,and the lower the stiffness of the board structure,the greater the maximum equivalent force applied.(2)from three kinds of board structure of the corner solder joint maximum tensile stress root mean square curve could be seen,were close to the BGA side of the solder joint maximum tensile stress.The same layout mounts one chip on the A board,B board,and C board solder joint maximum tensile stress root mean square in decreasing order,at the same time the vibration fatigue life of the solder joint in increasing order,so under vibration load,the lower the board stiffness,the greater the stress,resulting in PCB components were more likely to fail.4.The finite element numerical simulation analyzed of PCB assemblies of three board structures under temperature-vibration coupling was carried out to consider the random vibration problems of PCB assemblies of three board structures under 0°C,25°C,and 60°C environments,respectively.It was found that: comparing the first three orders of inherent frequencies of the specimens with different board structures of the same chip at 0,25 and60.It was concluded that the increase of temperature would lead to the decrease of the elastic modulus of the solder joints,which maked the inherent frequency of the board assembly decrease,which was consistent with the results obtained from thermal modal experiments;the PCB assembly with the same chip mounted on the three board structures was under the effect of temperature-vibration coupling,the higher the temperature at which the same board structure,the displacement suffered,the greater the stress.