A Study Of Mechanical Properties For Anisotropic Conductive Adhesive Film And Bonding Reliability For COG Assembly

Anisotropic conductive adhesive film (ACF) has attracted more and more attention as a new kind of green packaging bonding materials. Because of the lack in fundamental knowledge of ACF's mechanical properties and bonding reliability, the mechanical behaviors of cured ACF were comprehensively studied and the bonding reliabilities of COG (Chip-on-Glass) assembly were investigated with different conditions, moreover the interfacial stress of COG assembly was analyzed. All the studies were significant for the application of ACF in microelectronics packaging.ACF's mechanical properties were investigated considering the factors of time, loading rate and environment by the tests of creep, stress relaxation, uniaxial tension and temperature sweep. The results show that the ACF is a kind of nonlinear viscoelastic material and its mechanical behaviors depend on the testing temperature and loading rate obviously. The increases of temperature and loading accelerate the processes of creep-recovery and stress relaxation. The relaxing constitutive model and creep constitutive model for the ACF were constructed respectively and the new creep model of ACF with considering aging damage was developed based on time-aging damage superposition principle. Simulated results are found to agree very well with the experimental data about ACF's mechanical behaviors. The relation of long-term creep rupture time prediction of ACF under constant load is presented and validated.The bonding reliabilities and fatigue properties of COG assembly were investigated experimentally with various environments. The results show that the shear modulus and shear strength decrease with increasing temperature, and the shear strength and fatigue life decrease with increasing hygrothermal aging time, however increase firstly then decrease with increasing thermal cycling. The constitutive model was constructed to describe the adhesive properties of COG assembly and it is found that the predictions of the model agree with experimental results well. The relationship of loading and displacement was obtained. The damage parameter D was introduced into the constitutive model to reflect the effect of hygrothermal aging on the adhesive properties and fatigue life of COG assembly.The interfacial residual stress of COG assembly was analyzed and simulated by the new stress analysis model, FEM and others. The results show that the residual shear stress and peeling stress are present in the interface of COG assembly when produced and the shear stress decreases gradually because of the creep of the bonding materials. The new stress analysis model can predict the interfacial residual stresses for bonding assembly of thinner bonding layer simply and accurately.