Research On Technology Of Accelerated Testing Of Electronic Equipment With Multiple Failure Modes Under Thermal Cycling Loadings

With the development of science and technology,modern electronic equipment becomes more and more reliable.However,due to the structure becomes more and more complicated,the electronic equipment has many potential failure modes.The statistics of equipment hardware failures by the U.S.air force shows that: more than half of the military aircraft electronic equipment failures are related to the working temperature environment.There are two typical failure modes of the electronic equipment working under the thermal conditions: the failure modes caused by the dysfunction of the critical component(failure modes related to component),as well as the failure modes arising from the fatigue breaks of solder joints(failure modes related to solder joint fatigue).Therefore,the research on theory and methodology of accelerated testing of electronic equipment under thermal conditions is significative to the reliability assessment of modern complicated electronic equipment.At present,the accelerated testing methods with the purpose of assessing the reliability of electronic equipment mainly adopt constant-stress,step-up-stress,step-down-stress and progressive-stress,which can effectively stimulate the failure modes related to component.However,the solder joints in the electronic equipment need to be subjected to sufficient cyclic loadings until fatigue failure occurred.When the test temperature is loaded in the form of constant,step-up,step-down or progressive,the solder joints in the electronic equipment can not be subjected to cyclic loading.Therefore,the accelerated testing method adopting constant-stress,step-up-stress,step-down-stress and progressive-stress can not stimulate the failure modes related to solder joint fatigue effectively,and can not evaluate the reliability of the electronic equipment with the failure modes related to component and the failure modes related to solder joint fatigue.Therefore,this dissertation systematically studied the theory and methodology of the accelerated testing method which can assess the reliability of the reliability of the electronic equipment working under thermal environment efficiently and accurately.In this accelerated testing method,thermal cycling is appied as the testing environment,in which the failure modes related to component and the failure modes related to solder joint fatigue can be effectively activated.The reliability of complicated device working under thermal environment can be evaluated according to the test data.The specific works in this dissertation involve the analysis of failure mechanism and reliability modeling,the statistical analysis method and the optimal design method of test plan.The main contributions of this dissertation are summarized as follows:1.The reliability model of the electronic equipment working under thermal cycling conditions are studied.This is the basic of the statistical analysis method and the optimal design method of the thermal cycling accelerated testing.(1)To solve the problem that the accelerated thermal cycling testing ignores the influences on the failure modes related to component,the reliability model of the failure modes related to component under thermal cycling loadings is established based on the exponential distribution and the Arrhenius model.This model can describe the reliability of the failure modes related to component under different thermal cycling loadings effectively.(2)For estimating the fatigue life of the solder joint under different thermal cycling loadings more accurately,the Norris-Landzberg model is revised according to the results of the mechanisms analysis of the failure modes related to solder joint fatigue.The revised Norris-Landzberg model can described the influences of the creep and stress relaxation phenomenons on the fatigue life of the solder joint under thermal cycling loadings.Forthermore,the reliability model of the failure modes related to solder joint fatigue is constructed based on the revised Norris-Landzberg model.(3)The relationship between the reliability functions of different failure modes is described by the competing risking model,and the reliability model of the electronic equipment with multiple failure modes under thermal cycling loadings is established.2.The problems about statistical analysis of the thermal cycling accelerated testing of the electronic device with multiple failure modes are solved,and the statistical analysis method of the thermal cycling accelerated testing with independent failure modes based on CEM model and the statistical analysis method of the thermal cycling accelerated testing with dependent failure modes based on copula function are geiven respectively.(1)According to the failure modes that are sensitive to the low temperature,the limitations of the accelerated test using high-temperature only as the test environment are pointed out,and the statistical analysis method of the accelerated testing under high temperature and low temperature is presented,which is the basic of the thermal cycling accelerated testing statistical analysis method.(2)The data conversion method based on CEM model is studied to transform the data of the failure modes related to component.The statistical analysis method of the thermal cycling accelerated testing with independent failure modes based on CEM model is given.The corresponding Monte Carlo simulation method of the test data is presented,in which the concept of equivalent failure rate is proposed to simulate the data of the failure modes related to component.(3)According to the copula theory,the statistical analysis method of the thermal cycling accelerated testing with dependent failure modes is developed.In this method,the copula function is used to decribe the relationship of the reliability functions of different failure modes,and the estimations of the parameters of the reliability model and copula function are obtained by the IFM method.3.The problems about the optimal design of the thermal cycling accelerated testing plan are solved.The optimal design method based on the analytic and the optimal design method based on Monte Carlo simulation are studied respectively.(1)The optimal design method based on the analytic of the thermal cycling accelerated testing plan is put forward.The calculation method of the expected value of the failed sample number is given in the process of establishing the log-likelihood function.The D-optimal design method based on the Fisher information matrix and the optimal design method based on the asymptotic variance of reliability index are proposed respectively.(2)The optimal design method based on Monte Carlo simulation of the thermal cycling testing plan is studied.In this method,the statistical analysis results of all selectable testing plans are obtained through the two mainly process of data simulation and statistical analysis.The optimal test plan is acquired by comparing the statistical analysis results of all selectable testing plans.(3)The analytic method and the simulation method are contrastively analyzed though a simulation case.4.The thermal cycling accelerated testing of the chip capacitors and the chip resistors is carried out to demonstrate the feasibilities of the proposed methods,and the results show the efficiences of the proposed methods.In summary,the theory and methodology of accelerated testing with multiple failure modes under thermal cycling stress are systematically researched.The study in this paper has formed a set of theory and methodology for the reliability assessment of the complicated electronic devices working under thermal cycling conditions.At the same time,it enriches the content of accelerated testing theory and methodology.The results of this dissertation has an important theory and engineering value.