Study On The Reliability Of The PCB Assembly Under Different Environmental Condition

With the communication and computer technology improving,the electronic information technology has developed rapidly.Besides portable electronic products used in our daily life,such as cell phone and notebook computer,the electronic equipment was used more frequent in the industry of automotive and astronautics.No matter the electronic products used in daily or industry,the higher reliability was required in the different environment conditions.It became particularly important to analyze the reliability of the electronic devices under different using condition.In this paper,in order to study the reliability of the PCB assembly under thermal loading,mechanical shock loading and thermal-mechanical couple loading,the ANSYS(finite element software)was adopted to analyze the dynamics responses of the PCB assembly.By observing and analyzing the simulation results,the rules and reasons was found under the different using conditions.These data and conclusions improved the support of the statistics.Through the analysis of the temperature filed and thermal stress under the thermal surface loading and thermal cycling loading,the temperature filed and thermal stress distribution was obtained of the PCB assembly.It can find the most dangerous area of the solder joints.The results showed the thermal stress appeared near the BGA package pads on the one solder joint.Compared thermal stress distribution on the solder joints of the PCB assembly,the distribution of the thermal stress on side of the PCB assembly is greater than central area.The mode shape and natural frequency was obtained by modal analysis.The dynamics responses of the PCB assembly was obtained when the analysis of the drop loading was accomplished.Compared the results under different heights and different stiff targeted surface of dropping,the influence of the loading factor could be found.The PSD curve was obtained when the analysis of the random vibration was accomplished.The reliability of the random fatigue was verified by random fatigue calculation.The stress concentration area of the solder joints appeared near the interface between the BGA package and pads.The distribution of the stress on side of the PCB assembly is greater than central area.Compared the change of the modal parameter and the PSD curve under thermal and normal condition,it found that the natural frequency reduced and the PSD curve was forward.Compared the invalidation mechanism of drop loading under the thermal cycling and normal condition by experiment,the influence of thermal on mechanical loading was found.The results showed: when the PCB assembly were only subjected to drop loading without thermal cycling,the solder joint cracks appeared near the BGA package pads;when the PCB assembly subjected to drop loading and thermal cycling,the solder joint cracks appeared near the PCB pads.