| Electronic packaging polymer can protect chips from the impact of external harsh environment,especially physical effects such as impact and pressure,and chemical erosion such as water vapor and ultraviolet rays.At the same time,it can provide mechanical support and heat dissipation channel for circuits.It is widely used in information terminals,automotive electronics,drilling equipment,aerospace and other fields.With the increasing complexity and diversity of service scenarios of electronic products,electronic devices are often exposed to extreme high temperature environment.Due to the characteristics of polymer matrix composites,the outer epoxy molding compound is prone to high temperature oxidation,which may lead to the degradation of material properties and local stress mismatch,seriously affecting the service reliability and durability of electronic devices.At present,the research on the thermal oxidation behavior of electronic packaging polymer at high temperature and its influence on device reliability is relatively less.Strengthening the research in this field has important practical application value and guiding significance for the design and development of high temperature electronic components.In this paper,epoxy molding compound(EMC)is selected as the research object,and the high-temperature thermal oxidation behavior and related mechanism of EMC are systematically studied by using the methods of experimental research and numerical simulation,and the influence of thermal oxidation phenomenon on the reliability of electronic devices is explored.The specific work includes:Firstly,the thermal oxidation behavior and mechanism of epoxy molding compound at high temperature are explored,and the thermal oxidation diffusion model of epoxy molding compound is established.The correctness and accuracy of the model are verified by finite element analysis.In this study,DMA technology is used to obtain the elastic modulus E of molding compound,and the glass transition temperature Tg is obtained by analyzing tan?-T curve,it is found that with the increase of aging temperature and time,the elastic modulus of glass and rubber molding compounds increases significantly,after high temperature aging,the glass transition temperature of molding compound shows obvious differentiation,with lower Tg-1 and higher Tg-2.By comparing with the high temperature storage mold plastics in vacuum environment,it is clear that Tg-1 is the glass transition temperature of the oxidation core,Tg-2 is the glass transition temperature of the outer oxide layer,and the mechanical properties of the molding plastics are changed due to the high temperature oxidation.The ?1-T(deformation-temperature)curve and the coefficient of thermal expansion(CET)of the molding compound are obtained by means of thermal mechanical property analysis(TMA).It is found that the molding compound exhibits different thermal expansion coefficients under the same aging conditions.The smaller CET-1 is the coefficient of the unoxidized core,and the larger CET-2 is the coefficient of the outer oxide layer.The evolution of oxide layer in the process of high temperature aging of plastic is investigated by fluorescence microanalysis,it is found that with the aging time going on,the oxide layer grows and thickens,but the thickness of the oxide layer will eventually tend to a platform value.Considering the similarity between the solution of gas diffusion equation and heat conduction equation,the thermal oxidation diffusion model of EMC material is established,and then the oxidation diffusion of EMC material is transformed into heat conduction problem with ANSYS finite element software,the numerical simulation of different aging conditions shows that simulation results and the trend of experimental data is exactly the same,which verifies the correctness of the thermal oxidation theory and diffusion model of epoxy molding compound.Then,the effects of material composition and aging conditions on the mechanical behavior and thermal properties of molding compound are systematically studied.Two kinds of samples with different filler content are selected,the aging temperature is selected 175?,200? and 225?,and the aging time is selected 0h,100h,500h and 1500h.When the room temperature is not aging,the modulus of elasticity of the glass state of the molding plastics increases with the increase of SiO2 filler content,but the rubber modulus decreases,That is because SiO2 hinders the cross-linking and curing of molding compound,and the cross-linking reaction is not sufficient when the filler content is high,which affects the mechanical properties of rubber state.After high temperature aging,the lower the content of SiO2 filler,the more serious the oxidation degree of molding compound at high temperature,because the filler can prevent the diffusion of oxygen to the inner layer.When the composition of the material is identical,with the increase of aging temperature and time,the glass transition temperature Tg-1 of the core does not change,and the glass transition temperature Tg-2 of the outer oxide layer increases significantly.The elastic modulus E of the molding compound increases continuously,but the elastic modulus of the rubber state increases more than that of the glass state.The mechanical properties of the polymer are seriously degraded,and the material becomes hard and brittle.At the same time,the high temperature aging leads to the delamination of the molding compound,forming a new interface between the oxide layer and the core,due to the different mechanical properties of the two materials,such as elastic modulus,coefficient of thermal expansion and Poisson's ratio,a large internal stress is formed at the interface,which significantly accelerates the cracking and failure of the molding compound.Finally,high temperature aging experiments is carried out for typical electronic packaging devices to study the effect of thermal oxidation on the packaging structure and material properties,the thermal oxidation modeling and simulation of typical packaging structure is carried out to evaluate the effect of thermal stress on the mechanical behavior of the device.After a long period of high temperature aging test,the elastic modulus of EMC materials in electronic packaging devices increased significantly,relaxation occurs in the viscoelastic expansion material At the same time,the strength of the material decreases and the water absorption increases.Serious oxidation failure of solder joints in package interconnects is observed by micro oxidation technology,it can be seen that the high temperature thermal oxidation behavior seriously affects the service reliability of electronic packaging structure.In order to accurately evaluate the thermal mechanical behavior of electronic packaging devices during high temperature storage,the quantitative relationship among aging temperature,aging time and elastic modulus should be clarified.In this study,the change curve of EMC elastic modulus with aging conditions was obtained by Origin software and Sigmoid function fitting,and the regression equation is established.Therefrom,the EMC elastic modulus data under any aging temperature and time can be obtained.Then,four models with different oxidation degrees are selected as the research objects,and the package size and material characteristic parameters are clarified.The thermal stress coupling analysis of the device is carried out by ANSYS finite element software to obtain the internal stress distribution of the package structure,it is found that the Von Mises maximum stress is located at the interface between the chip and the plastic,with the increase of aging temperature and time,the change of the modulus of the outer molding compound causes more serious stress mismatch,after aging at 175? for 1500 hours,the maximum stress of the device increases by 58%compared with that of the device without aging.It is proved that the thermal oxidation behavior seriously affects the service reliability of the device.In summary,this paper takes electronic packaging polymer(epoxy molding compound)as the research object,carries out in-depth high-temperature aging experimental research,and reveals the thermal oxidation behavior and mechanism of epoxy molding compound at high temperature,the mathematical model describing the thermal oxidation behavior of epoxy molding compound is explored and established,and carries out the finite element analysis and verification;in addition,the effect of thermal oxidation on the mechanical behavior of electronic devices is studied by numerical simulation,and the thermal stress state of packaging devices is evaluated.This research can provide reference for the design and development of high temperature electronic devices,and provide theoretical support for the evaluation of high temperature packaging reliability and durability and failure prediction. |
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