Research On Technology And Mechanism Of P(EO)n-LiX And Al Joining For Bonding Packaging

With the rapid development of industrial economy,The number of terminal products will reach an unprecedented scale,also the market demand for MEMS devices and sensors increase rapidly.Its application has grown to all walks of life.Packaging is also one of the most important links in the manufacture of MEMS devices,its quality will directly affect the service life of MEMS devices.Polymer solid electrolyte is a kind of functional material developed in recent years.Due to the abundant source of raw materials for the main polymer,compared to other inorganic materials,it's easy to process and easy to modify,this unique structure made it work as packaging material for MEMS devices,therefore,Polymer hasirreplaceable excellent properties,which can further promote the development of MEMS industry technology.In this paper,polyethylene oxide?PEO? is first chosen as the main material,addition of different lithium electrolytes by using high energy ball grinding,design and prepare Ionic conductive polymer solid electrolytes suitable for anode bonding with metal Al,discussing the influences of the ball milling time and speed on the ball milling quality,then determine the type and content of lithium salt;Using asuper-depthmicroscope,X-ray diffraction,differen-tialscann-ingcalorimetric DSC,the complexation mechanism of P?EO?_n-LiX was studied by Fourier infrared spectroscopy and UV absorption spectroscopy.To study the influence of different kinds and content of lithium salt on the crystallinity of polymer solid electrolytes.At the same time,the Ionic conductivity of high molecular solid electrolyte P?EO?n-LiX with different lithium salt types and content was measured by AC impedance and analyzing the mechanical properties of high molecular solid electrolyte P?EO?_n-LiX.The results show that adding different lithium salts and increasing their content can effectively hinder the crystallization of PEO,increase the proportion of amorphous phase,lower glass transition temperature,and improve the complexation degree;thus lead to the increase of room temperature conductivity of P?EO?n-LiX;the ionic conductivity of selected lithium salts is Li PF₆>LiClO₄>LiBF₄ in turn;The results of compressive and hardness tests show that lithium salt also affects the mechanical properties of the main PEO.Under the same conditions,the mechanical properties of PEO-LiClO₄ were the best,because of the stronger acidity of perchloric acid and stronger self-plasticizing effect.The mechanical properties of PEO-LiBF₄ is the second and PEO-LiPF₆ is the worst.Secondly,the self-made PEO-LiClO₄ with good comprehensive performance was used as the bonding cathode material to study the anodic bonding process with metal aluminum.The variation of bonding current and time during bonding of PEO-LiClO₄ with metal aluminum under different bonding voltages was studied.The bonding quality of PEO-LiClO₄ bonding with metal aluminium was analyzed,and the optimum process parameters were determined.The microstructure of bonding interface between PEO-LiClO₄ and metal aluminium was analyzed by ultra-depth-of-field microscopy,and the bonding mechanism was revealed by infrared and energy spectroscopy.It is considered that,at the same bonding voltage,during the bonding process of polymer solid electrolyte PEO-LiClO₄ with different complex ratios,the more the lithium salt content,the larger the instantaneous peak current.Within the range of selected process parameters;when other conditions are fixed,as the bonding voltage increases,the peak currents are sequentially arranged in the order of U800>U700>U600>U500>U200,when the bonding voltage of 800V and the content of LiClO₄ is 20%,the peak current is the highest and the combination rate is the best.The tensile strength of the bonding interface between PEO-LiClO₄ andaluminum at room temperature indicated that the strength was 7.03MPa when the lithium content was 5%;When the lithium content was 10%,it was 8.32MPa,and when the lithium increase to 20%,the tensile strength of the bonding interface decreased.The results of microstructure analysis of the bonding interface show that:the paraslastic distribution of PEO molecular chain is more conducive to the transmission of lithium ions in the electric field,and the effective bonding mechanism of the interface lies in a series of actions of"mechanical interlocking-electrostatic adsorption-ion migration-ion diffusion-ion coordination exchange".First close contact each other polymer solid electrolyte PEO-LiClO₄ chain segment metal aluminium each other under the action of temperature and pressure on the surface of the squeezed into their respective ravines,clearance and electricity,interface in a strong electrostatic field under the action of the PEO-LiClO₄ formed certain polarization area,PEO-LiClO₄ electric dissociation,solve the complex of Li⁺ in strong electric field under the action of formed from anode to cathode of directional movement,so as to make the positive and negative charge on the two interface adsorption to each other,to form the strong electrostatic attraction,Al³⁺ indicated by anode diffusion to the interface,In addition,Li+ was substituted to coordinate with the ether oxygen atom of PEO in the polymer to form an intermediate transition layer.Through infrared analysis,the presence of C=C and aldehyde group new functional groups was also found in the intermediate transition layer,and the new functional groups were also the basic components of the interface.MARC finite element analysis showed that the PEO-LiClO₄/Al/PEO-LiClO₄ three-layer symmetrical design,relative to the two-layer bonding structures,could effectively reduce the deformation of the specimen,thus greatly improving the quality of MEMS devices.