Analysis of ACA/ACF package using equivalent spring method

Flip-chip-on-glass (FCOG) assembly technology using anisotropic conductive film (ACF) is being developed for fine pitch interconnections between driver ICs and flat panel displays. Conductive adhesives offer advantages in terms of fine-pitch capability and environmental compatibility. Anisotropic conductive films (ACF) are composed of adhesive resin and conductive particles, such as metallic or metal-coated polymer particles. Unlike solder type flip chip interconnection, electric current passing through conductive particles becomes the dominant conduction path. Interconnections between the particles and conductive surfaces are constructed by elastic/plastic deformation of conductive particles with contact pressure, which is maintained by tensile stress in the adhesive. Loss of electric contact can occur when the adhesive expands or swells in the Z-axis direction, but delamination and cracking can occur in the adhesive layer when the tensile stress is excessive. Process simulations and reliability modeling are performed, and nonlinear finite element simulations are used to study the contact force developed and relaxed within the interconnect during processing and environmental effects such as high temperature thermal loading. In addition, a parametric study was also performed. For better performance and reliability, variables such as ACF materials and processing conditions are discussed. Furthermore, a novel method called the equivalent spring method is developed; this methodology could significantly reduce the analysis CPU time and make ACA/ACF process modeling and contact analysis possible.