Failure Analysis And Optimization Strategy Study On High Density Ceramic Column Grid Array Package

Due to the advantages such as solder column structure,high electrical interconnection density,good thermal and electrical properties,compatibility with standard surface mount assembly processes,high density ceramic column grid array(CCGA)package has been increasingly applied in the fields such as aviation and aerospace that needs high device reliability requirements.On the other hand,high-density CCGA package has the characteristics of high density,large area array and high weight,which will make the package itself more susceptible to thermal,vibration,and thermal vibration coupling stress in actual usage environments,leading to device failure.Therefore,study on the conducting failure analysis and related optimization strategies for high-density CCGA package under thermal,vibration,and thermal vibration coupling is of great significance to improve its application reliability.Combining engineering applications and industry demands,this thesis takes typical high-density CCGA package as the research object to study the effects of thermal cycling,random vibration,and thermal vibration coupling stress on the reliability of high-density CCGA package.The weak areas of high-density CCGA package,sensitive areas of solder columns,and microscopic morphology failure characteristics are studied intensively.The typical failure modes and mechanisms under different stresses are preliminarily proposed.Optimization and simulation analysis of key factors which affect package reliability are conducted,and the application optimization strategies are proposed for the improvement of product design,reliability enhancement,engineering application and development of high-density CCGA package.The work and achievements of this thesis are as follows:1.Study on failure analysis of high density CCGA package under thermal cycling conditions.Based on the typical application scenarios,experiments were conducted and the microscopic characteristics of failure are thoroughly studied.Three typical failure modes have been proposed,including crack propagation along the plane of the necked portion at the bottom of the solder column,lateral or oblique propagation along the necked portion at the top,and propagation along the IMC plane of the ceramic substrate.A cross scale high-density CCGA package board level model was constructed to study the distribution and variation patterns of equivalent stress,equivalent strain,equivalent deformation,plastic strain,creep strain,etc.from multiple dimensions.It is shown that the failure sensitive areas are the four corners of the package.The danger range for solder column failure is 0.15～0.60 mm and2.17～2.43 mm.The equivalent stress,equivalent strain,and plastic stress in the top section vary greatly,making the solder column more prone to cracking and fracture.The finite element numerical analysis results are consistent with the test results.Under the interaction of fatigue and creep mechanisms,cracks form and propagate in encapsulated solder columns,leading to failure ultimately.2.Study on failure analysis of high density CCGA Package under random vibration conditions.The techniques of designing and optimizing vibration fixtures for top load capacity are made a breakthrough.A hexahedral vibration fixture that is more suitable for high-density CCGA package was designed.After optimization,the first-order natural frequency of the fixture is increased by 43.9%,the quality is reduced by 22.2%,and the full load error is relatively reduced by 60.3%～69.1%,which greatly improve the test accuracy to support the development of reliability testing.The microscopic characteristics of failure after vibration testing are thoroughly studied.Three typical failure modes are proposed preliminarily,including transverse propagation of cracks along the plane of the top necking area of the solder column,oblique propagation of the bottom necking area to the solder body,and oblique propagation to the IMC.The finite element numerical analysis based on modal characteristics,equivalent stress,and the distribution and variation law of equivalent strain shows that although the stress generated by random vibration is different from that generated by thermal cycling stress,the four corners of the package are still failure sensitive areas under random vibration conditions.The simulation analysis results are consistent with the experiment results.Under the action of mechanical fatigue mechanism,cracks in package solder columns form and propagate,ultimately leading to failure.3.Study on failure analysis of high-density CCGA Package under thermal vibration coupling conditions.A high-density CCGA package thermal vibration coupling test based on actual operating conditions is designed and carried out for the first time,which solves the problem of highly reliability applications without basic data support.The failure analysis study on appearance and microscopic characteristics is carried out,and a typical failure mode which is transverse propagation of cracks along the plane of the necked end at the top of the solder column is preliminarily proposed.Based on sequential coupling modeling and simulation techniques for high-density CCGA package,the modal characteristics,equivalent stress,and equivalent strain distribution and variation rules are compared and studied.The results show that the four corners are still the failure sensitive regions of high-density CCGA.Compared to a single stress,the thermal vibration coupling significantly increases the stress and strain levels of the solder column.Compared with a single random vibration,the equivalent strain and equivalent stress of thermal vibration coupling increase by 2.1 and 1.7times,respectively.Under the combined action of thermal fatigue mechanism and mechanical fatigue mechanism,the package solder column fails.4.Simulation analysis and optimization strategy study based on experimental design.A comparative study is conducted on 45 test combinations based on response surfaces and 27 Taguchi test combinations based on orthogonal tables.With the maximum equivalent stress and the maximum equivalent effect as optimization objectives,quantitative analysis is conducted to provide key parameters that affect the reliability of high-density CCGA packages.The results show that the height and diameter of the solder column have the greatest impact on the reliability of CCGA package.The proposed simulation analysis methods based on experimental design in this thesis can be applied in product design,selection,and application processes;The proposed optimization strategies such as reinforcing edges and corners with peripheral multi ring solder columns,selecting ceramic substrates with less difference in coefficient of thermal expansion,and conducting empty pin redundancy or grounding redundancy design for pins in sensitive areas can be as a reference for improving the reliability of high-density CCGA package devices and system applications.