Research On Several Failure Problems Of Defective Layered Structure

In this paper,the influence of defects or cracks on the performance and life of layered structure is analyzed base on the delamination of microelectronic packaging and the hydrogen blister corrosion failure in petrochemical equipment.The failure mode,failure mechanism and failure cause of the defect layered structure are analyzed.For delamination failure of structure in microelectronic packaging,in this study,a circular interfacial defects with elastic constraints at the edge between the die-attach and the substrate in electronic packages are analytically modeled to investigate the effect of thermal misfit stress on the steam-driven delamination during the solder reflow process.Based on Love-Kirchhoff plate theory,analytical solutions of strain energy and strain energy release rate of circular delamination under the combined action of steam pressure and thermal stress are derived.By comparing the energy release rate of circular delamination under the action of steam pressure with and without thermal stress,the contribution of thermal stress to the energy release rate is assessed quantitatively.Further,the contribution of thermal stress to the extension of elliptic delamination is studied numerically.This study provides a more accurate model for prediction of delamination extension and failure evaluation of electronic packages and brings new understanding on the role that thermal stress plays in promoting steam-driven delamination during the solder reflow process in electronic packages.For the failure caused by hydrogen blistering in petrochemical industry,the diffusion and aggregation behavior of hydrogen induced by stress during the process of hydrogen blistering formation was studied,with the effect of hydrogen diffusion on the stress field in the crack tip region taken into account.This work is aimed to investigate the evolution of hydrogen concentration,hydrogen pressure and stress intensity factor at the crack tip with time.By using software ABAQUS,the dynamic process of hydrogen diffusion and build-up of stress field at the crack tip,as well as the interaction between hydrogen diffusion and stress concentration are investigated through a fully coupling analysis.Initiation of extension of hydrogen blistering will be determined by crack propagation criterion in fracture mechanics.Under stress induction,hydrogen diffuses towards the vicinity of the crack tip continuously,and hydrogen concentration,hydrogen pressure and stress intensity factor in the regions near crack tip increase exponentially with time.Under the action of concentration gradient,hydrogen diffuses into the interior of material.The stress field induced by hydrogen pressure will promote the diffusion behavior of hydrogen,and the larger the stress field,the more obvious the promoting effect.This makes the hydrogen concentration in the defect increases,and the hydrogen pressure increases as well.When the hydrogen pressure at the defect is equal to the local fracture strength of the material,the defect will extend and form a hydrogen blistering.This process happens again and again until the hydrogen blister.