Design and understanding of anisotropic conductive films (ACFs) forLCD packaging

摘要

Anisotropic conductive films (ACF) composed of an adhesive resinand fine conductive fillers such as metallic particles or metal-coatedpolymer balls are key materials for fine pitch chip-on-film (COF) andchip-on-glass (COG) LCD packaging. To understand and design betterquality ACF materials, a conduction model with a physical contactmechanism was simulated and experimentally proved. To understand thecontact area changes, two pressure dependent models - (1)elastic/plastic deformation and (2) FEM - were developed and proved bytesting various ACFs. Experimental variables such as bonding pressure,and the number, size, mechanical and electrical properties of Ni powdersand Au-coated polymer conductive particles were applied. The modelsagreed well with experimental results, except at higher bondingpressures. In general, as bonding pressure increases, sharp decrease incontact resistance followed by a constant value is observed afterreaching a critical bonding pressure. However, excessive bondingpressure inversely increased the ACF connection resistance. If moreconductive particles were added, the connection resistance rapidlydecreased to a constant. This is the counter-effect of two opposingfactors: resistance increase by decrease in contact area per particleand resistance decrease by increased conduction path numbers. Also,environmental effects on contact resistance and adhesion strength suchas thermal aging, temperature/humidity aging and temperature cyclingwere also investigated. As a whole, better design of ACF materials canbe achieved by understanding the ACF conduction mechanism