Mechanical Simulation Analysis Of System In A Package(SiP) With Electron-thermal-mechanical Effect

SiP(System in a Package)is a subsystem that encapsulates multiple chips or components through bonding wire,flip-chip welding,chip stacking and other packaging technologies.It has the advantages of informatization,intelligence and integration.However,with the requirements of miniaturization,modularization and high reliability of electronic devices,the reliability of SiP electronic packaging is severely challenged.In this thesis,the sensitive environmental conditions are determined by analyzing the application environment of a SiP,and the sensitive parts are determined by common failure analysis.ANSYS finite element software is used to simulate the reliability analysis of the overall and local sensitive parts of SiP under the coupling conditions of thermal stress,mechanical stress and electro-thermal multi-physical fields.The results show that:(1)For the reliability analysis under the condition of thermal stress.It is analyzed that the thermal stress sensitive environment of SiP is mainly the temperature cycle condition,and the sensitive parts are the four sides and four corners of the solder ball layer in the TSV(Through Silicon Via)adapter plate.Due to the viscoplastic constitutive reason,the structural reliability of the solder ball at low temperature is lower than that at high temperature,and the maximum stress occurs at the joint of the four corner solder ball and the TSV adapter plate at-55 ? The thermal fatigue life of the composite is obtained,which meets the requirements of application environment.According to the thermal reliability analysis of the local position,it is found that the weak position of the bonding wire is at the pad,which is prone to fracture;the weak position of the chip stack is at the four corners between the bonding layer and the chip,which is prone to chip warping;the weak position of flip chip is at the bottom and four corners of the ball layer,which is prone to root fracture.(2)For the reliability analysis under the condition of mechanical stress.The mechanical stress sensitive environment of SiP is mainly mechanical shock,random vibration and constant acceleration.The sensitive parts are the four corners and four sides of the outer pin.The maximum stress under random vibration is only 10% of that under thermal stress.The main failure reason is mechanical fatigue life.The outer pin is in the condition of random vibration through Steinberg three interval method and morrow modified Coffin Manson formula the fatigue life of the system can be predicted to meet the application requirements of aerospace environment.According to the mechanical reliability analysis of the local position,it is found that the displacement of the bonding wire is large in the middle section under the impact condition,which is easy to lead to the failure of the bonding wire;the outer pin has a cushioning effect on the impact environment,and the root has broken.(3)For the reliability analysis under the condition of multiple physical fields.Through the simplification of coupling relationship,the forms of electrothermal unidirectional coupling and thermodynamic bidirectional coupling are determined.Through the reliability analysis,it is found that the damage caused by thermal stress is more obvious than that caused by mechanical stress.The fatigue life under coupling condition is obtained by the method of damage superposition,which meets the requirements of aerospace environment application.The work in this thesis improves the process of SiP reliability analysis,and carries out the reliability analysis under the sensitive environment for the whole SiP,so as to determine the weak position and guide the reliability analysis of the detailed structure.Compared with the reliability analysis of a single detailed structure,it is more practical for product design and engineering application.