Fatigue Damage Of The Electronic Packaging Under Random Vibrations

With the rocket’s mechanical environment is getting worse and worse,the functions of the instrument and equipment are more diversified and the volume is more miniaturized.The instrument and equipment are not only more powerful and higher in temperature,but also the vibration and impact environment is very harsh.At present,the failure mechanism analysis and damage life assessment of instruments and equipments have widely developed in foreign countries,while domestic research in this field is very few.It is of great significance to improve the reliability of electronic equipment by investigating the damage mechanism of instrument equipment and evaluating the equipment damage life.In some cases,the failure caused by vibration shock becomes the main cause of failure of electronic equipment.Exploring the damage of electronic equipment in the environment of vibration and impact mechanics,and evaluating the mechanical response through life simulation to evaluate the lifespan,and combining with the test to verify each other is the main approach way to the study.In actual conditions,the multi-axial vibration state is the mechanical environment that aerospace products mainly suffer during work.The study of the multi-axial mechanical environment and the comparison of the traditional 3 orthogonal axes with the sequential application of the excitation mode are the main directions for the study of the vibration life assessment.In this paper,the modal and transfer characteristics of a typical CQFP packaged electronic equipment instrument are compared with the transfer functions under uniaxial and multiaxial excitation.It is found that multi-axial excitation can stimulate more modal and more energy of the structure.The three-interval method,Dirlik distribution method,and rainflow counting method were used to evaluate the life of random load history and equipment weak links under different conditions.The accuracy of the distribution of stress rain flow amplitudes under different spectral width coefficients was analyzed.It is found that the Gaussian distribution corresponding to the three-interval method has a good description of broadband narrowband distribution.T he Dirlik distribution is better in the description of the distribution of stress rain flow amplitudes with larger spectral width coefficients.In general,the frequency domain method can be used to compare the life expectancy conservatively with uniaxial and multiaxial excitation.It is found that the failure position and time are different under different load conditions,and the life under multiaxial vibration is far less than the uniaxial excitation life.Finally,by comparing the uniaxial vibration and multiaxial vibration damage,according to the ratio of the two,the uniaxial excitation conditions are amplified to obtain an excitation amplification method that makes the cumulative damage equal to the unit time and verify the feasibility.For the experiment,the optical modal test was used to obtain the first three modes of the method,and the resulting frequencies and mode shapes were used for the correction of the finite element model.According to the normal frequency response function of the test and simulation,the damping is further modified.Finally,the normal and multi-axial vibration tests under the same load were carried out to compare the damages produced at the same time.