Glass/aluminum Multilayer Residual Stress In Anodic Bonding Joint Strain Numerical Simulation Research

Multi-layer anodic bonding has been one of the key technologies to manufacturingmicro-electro-mechanical system （MEMS） devices. However, residual stress and deflection willpresent in the bonding after cooling, which directly affect precision and service performances ofthe bonding, reduce load capacity of the bonding. In this paper, residual stress and strains duringcooling process of multi-layer anodic bonding have been studied on the basis of anodic bondingprocess. The investigation has theoretical meaning and practice guidance for improving qualityof multi-layer anodic bonding.Firstly, the five-layer glass/aluminum anodic bonding experiment has been designed andconducted by using the public anodic bonding method. The composition and microstructure inthe interface between the glass layer and the aluminum layer have been analyzed, andmechanical properties of the bonding have been tested. The results of SEM and EDS show thatthere is a transition layer with5m thickness between the glass and aluminum interfaceproduced during the bonding process as a result of element diffusion form the glass layer andthe aluminum layer. There are elements of oxygen, sodium and silicon from the glass layer andaluminum element from the aluminum layer, which present symmetric decreasing andincreasing gradient distribution in the both sides of the aluminum layer. The results of XRDtesting show that structures in the transition layer are almost Al₂SiO₅, SiO₂and a little ofAl₂O₃.Secondly, residual stress and strain distribution in the seven-and nine-layerglass/aluminum anodic bonding during cooling is analyzed by means of nonlinear finiteelement simulation software MARC. The results indicate that residual stress and straindistributions and values found to be the same nearly. The maximum equivalent stress locates atthe center area in the transition layer with the value of about1.08×10⁹Pa; The equivalent stressvalue in the aluminum layer reach its yield stress, so aluminum occur plastic deformationduring the cooling process; The stress component along thickness direction are compressivestresses in all layers, and the maximum value is in the aluminum layer; The stress componentalong the direction perpendicular to the thickness direction are tensile stresses in both of thealuminum layer and the transition layer, but compressive stress in the glass layer, and themaximum value is in the aluminum layer; the maximum shear stress locates in the transition layer. The equivalent strain locates at the center area in the aluminum layer with the value ofabout2.56×10^-2.Finally, residual stresses and strains in the two-, three-, five-, seven-and nine-layer anodicbonding samples were analyzed by comparison, and residual stress and strain mathematicalmodels for multi-layer bonding have been established. The comparison results show that themaximum deflection occurs in the two-layer bonding due to its non-symmetric structure;deflections in the other layer bonding samples increase with increasing layer number, butsmaller due to its symmetric structure. The maximum equivalent stress locates at the centerarea in the transition layer, and increase with increasing layer number. Overall, the minimumresidual stress and strain is in the three-layer bonding, and residual stresses and strains arealmost the same in the other layer bonding samples. Therefore, multi-layer glass/aluminumbonding with symmetrical structure can decrease deflection at a certain extent, which has animportant value for structure design and bonding process of the MEMS devices, and thequality promoting of the MEMS.