Analysis Of The Reliability And Fatigue Life Of BGA Solder Joints

Multifunctional integration,convenient and low price trend of the electronic products will inevitably lead to light,thin,short and the miniaturization technology demand,which makes the electronic packaging technology become relatively independent and the competitive field in the microelectronics industry all over the world.The reliability of the solder joints self-assembly and the fatigue life of solder joints are the important norm of the reliability of the packaging components.As the decreasing of the package dimensions and the increasing packaging density,it is difficult to observe the process of the solder joints self-assembly through the naked eye.Therefore,how to guarantee the reliability of the self-assembly process,enhance the yield of welding,and ensure the solder joint fatigue life becomes the focus in industry.As the BGA packaging is the main packaging form at present,the reliability of the self-assembly and the fatigue life of the BGA solder joints group are particularly important.This dissertation studies on the reliability of BGA packaging,the stress and fatigue life of BGA solder joints.In this dissertation,the BGA solder joints shape,the warpage and the yield of self-assembly of BGA packaging,the thermal residual stress of BGA solder joints and the stress distribution on the cross section of BGA solder joints,the fatigue life of BGA solder joints are discussed,and some guidance and suggestions are put forward for the technological process.The main achievements and results are listed as follows:1.Based on the analysis of surface tension and wettability of the liquid,experiments were performed to analyze the influence of the volume of the liquid on its contact angle.Then,according to the change rule of the contact angle of the droplet boundary at the structure changes of solid material or the junction of two different solid materials,the concept of "contact hinge" is put forward,which provides the basis for the subsequent more accurate simulation of solder joints liquid bridge.Considering the volume constraints,a Young-Laplace equation which the supplementary angle of the contact angle is regarded as the independent variable is proposed to simulate the different boundary conditions and different structures of BGA solder joint shapes,and its 3D simulation forms are obtained.Meanwhile,the solder joints liquid bridge stiffness curve which characterizes the solder joints force and the liquid bridge height is obtained.Considering the inevitable manufacturing error of the solder joints volume,the solder joints liquid bridge stiffness curves of different volumes are solved,which provides the basis for subsequent self-assembly reliability analysis.2.Based on the lamination theory of the elastic mechanics,a three layer board model of the resin,Si chip and ceramic substrates is modeled to analyze the warpage of BGA packaging device with the freedom constraints,and the warping deformation law of devices with the changing temperature is obtained.Considering the inevitable manufacturing error of the solder joints volume and the randomness of solder joints positions,the self-assembly of device is analyzed based on the solder joints liquid bridge stiffness curves of different volumes,and the judgment standard of solder open circuit and short circuit is obtained.The yield of the self-assembly of the type of device can be got by numerous analysis of the same device.The influence of the deviation rate of solder joints volume and pad diameter on the yield of self-assembly is achieved by changing its size,which has a certain guiding role on the production process.Finally,considering the development direction of the current packaging device,the match relation between the mean volume of solder joints and pad diameter of 0.35 mm and 0.3 mm pitch device are simulated,the matching value which can meet the current standard is obtained.It provides a reference for the future development of packaging device,and also provides guidance for design process parameters of the device.3.The BGA solder joints temperature residual stress in the service is analyzed as the solder joints is regarded as a variable cross-section rod structure.Considering the warpage and the thermal expansion deformation of each layer of the device,the temperature residual normal stress and residual shear stress of the BGA solder joints on different positions are simulated.The influence of the thickness of the resin and the PCB on the residual stress of BGA solder joints are discussed to provide certain guidance for the process design.The normal stress and shear stress distribution of the BGA solder joints cross section are analyzed using a circular cross section of circular arc crack model of BGA solder joints.The primary stress direction angle and the maximum nominal stress near the crack tip with the changing of the crack propagation law for different cross section shapes and different cracks are analyzed.The importance of the solder joint cross section shape and the crack shape on the solder joint fatigue life analysis is obtained.4.The fatigue life of BGA solder joints is analyzed.Based on the Paris experience formula of the fatigue life,a circular arc plate edge on circular cross section crack extension model of BGA solder joints is put forward to predict the fatigue life of BGA solder joints.It is summarized that the thickness of resin and the PCB should be reduced as far as possible under the condition of the process allows to increase the fatigue life of BGA solder joints.Furthermore,a force powered accelerated fatigue life machine and integrated test specimens are designed and produced based on the products provided by ZTE to observe the position of the fracture surface and to analyze the service life of the solder joints.A method to judge the position of the fracture surface of the solder joints is proposed and the fatigue life and the simulation and experimental results for the fatigue life of the solder joints are agree well.