Prediction Of Solder Joint Shape Of Multiple Devices And Reliability Analysis Of Temperature Cycle For Complex Assembly

Printed circuit board assembly(PCBA)is an important carrier for the realization of the function of electronic products.With the rapid penetration of electronic products into various fields,reliability research for products has become one of the important research topics.The researches show that 50%of electronic products failure is caused by solder joint failure,and the bad temperature load has a significant impact on the service life.In addition,the welding process conditions determine the shape of solder joint and affect the fatigue life of solder joint,thus affecting the service life of products.In this paper,based on the principle of minimum energy,the solder joint morphology of three typical packaging devices is simulated.Combined with theoretical analysis and finite element simulation,the stress-strain behavior of solder joint of PCBA under temperature cyclic load is analyzed.The Coffin-Manson equation considering the plastic strain is used to calculate the temperature cycle life of the PCBA.Finally,the influence of the device layout,thickness of PCB,package type and clamping method on the life of the printed board assembly is studied.The main work of this paper is summarized as follows:1.Taking spherical solder joints of BGA package,L-type solder joints of QFP package and solder joints of surface mount components as research objects,the corresponding solder joint models are established by Surface Evolver.Based on the principle of minimum energy,the solder joint shapes of 14 types of devices in three package types under the conditions of 0.10mm,0.12 mm,0.15 mm,0.18 mm and 0.20 mm solder paste thickness are simulated and predicted,and the accuracy of the simulation is verified by the slice experiment.The influence of solder paste thickness on solder joint shape are analyzed.The results show that with the increase of solder paste thickness,the height and diameter of BGA Solder joint,the wetting range and climbing height of QFP solder joint,and the climbing height and wetting range of surface mount components solder joint show an increasing trend,and the solder joint morphology is gradually full.2.On the basis of the solder joint shape,the PCBA model is established.The Anand viscoplastic unified constitutive model is used to describe the thermodynamic characteristics of Sn63Pb37 solder under temperature cycling conditions.The thermal-structure coupling analysis is carried out by ANSYS Workbench software to determine the dangerous solder joint.The stress and strain response of PCBA under cyclic temperature loading from-55?to 125?is analyzed.The life of PCBA with different solder paste thickness is predicted by Coffin-Manson equation based on plastic strain.The results show that the dangerous chip is located at the edge of the PCB layout and the dangerous solder joint is close to the bolt hole.The temperature cycle life of the module increases with the increase of the solder paste thickness.When the thickness of solder paste is 0.2 mm,the life is the longest,which is 500hours.3.Nine sets of finite element models of PCBA are established,and their temperature cycle life and the common characteristics of components are analyzed.According to the statistical results,the test board model is established to study the effects of device layout,PCB thickness,chip package type and fixed support mode on the temperature cycle life of PCBA.The results show that the thermal fatigue life of solder joint is the longest when the device is placed in the inner non-center of the layout,which is 22071 hours.When the device is close to the bolt fixing hole,the thermal fatigue life of solder joint is the worst,which is1493 hours,and the solder joint life decreases by 83.2%.And the solder joint life near the long edge of the device is longer than that near the short edge.Meanwhile,The way of fixing has a significant effect on the reliability of solder joints.The results also show that the thermal fatigue life of solder joint can reach 4.5×10~5hours when the PCBA is fixed on one side,which is much greater than that of the two-sided fixation.When the two long sides are fixed,the thermal fatigue life of solder joint is the worst,which is 933 hours.The research work in this paper can provide some references for the reliability design and assembly process of PCBA.