Study On The Process And Mechanism Of Chip-Anisotropic Conductive Film-Resin Substrate Ultrasonic Bonding Interconnection

Due to its lead-free, interconnection of small pitch, high packing density, low cost advantages, Anisotropic Conductive Film (ACF) is widely used as a new green electronic packaging materials. At present, the interconnection of anisotropic conductive film-chip-substrate is mainly carried out by thermo-compression bonding process. However, long bonding time and high bonding temperature will easily damage the chip circuit, and cause a large thermal deformation and residual stress, which severely reduce the reliability of the ACF bonding devices. Therefore, this paper proposes the use of the horizontal ultrasonic vibration to accomplish the interconnection of the chip-ACF-FR4resin substrate. Through the experimental research and numerical simulation method, the effects of the bonding process parameters on interconnection quality of chip-ACF-FR-4resin substrate are studied, and the optimized ultrasonic process is obtained. The main work of this paper includes:(1) By ultrasonic vibration bonding and shear strength tests, the effects of the ultrasonic bonding process parameters on the bonding strength of ACF assemblies were investigated, the results show that:the ultrasonic power and ultrasonic bonding time greatly affect the ACF bonding strength of the ACF assembles while the bonding force and temperature of the substrate slightly affect the ACF bonding strength. The best ultrasonic bonding process parameters are the ultrasonic power is about2.80W, the ultrasonic bonding time is about2500ms, bonding forces can be selected form12to30N, the substrate temperature ranges from50to80℃, at this time the bonding strength of the ACF assembles can reach32N.(2) By the Fourier Transform Infrared Spectroscopy analysis method, the mechanism and the effects of the ultrasonic bonding process parameters on the curing degree of ACF material were studied. The results show that:the ultrasonic power and ultrasonic bonding time greatly affect the curing degree of ACF, while the effects of the bonding force and substrate temperature are slight. The curing degree of ACF can be reach90%under the optimized ultrasonic bonding process parameter to meet the requirements of reliability of ACF interconnection devices; A mathematical model describing the relationship between the curing degree of ACF and the ultrasonic bonding process parameters was established. The model can be used to accurately predict the curing degree of ACF after ultrasonic bonding.(3) The numerical simulation of the shear failure process of ACF assembles has been realized by the finite element analysis software ABAQUS. The results show that the exponential cohesive zone model realized by VUMAT subroutine could more accurately simulate the shear failure process of ACF assembles than the bilinear cohesive model. In the exponential cohesive zone model, the cohesive strength and cohesive energy are the main parameters affecting the simulation accuracy, and to determine in the optimization the bonding process parameters of the ACF bonding interface cohesive parameters were the characteristic length δ=4μm, the cohesive strength τmax=12MPa, cohesive energy φ=55.96J/m2.(4) A mathematical model describing the relationship between the ultrasonic bonding process parameters and cohesive strength and cohesive energy of the ACF assembles was established to provide a theoretical basis for the bonding strength prediction of the ACF assembles in the production practice.