A Study on the Magnetic Dispersion of the Conductive Particles of Anchoring-Polymer-Layer Anisotropic Conductive Films and Its Fine-Pitch Interconnection Properties

Abstract

As the display resolution has been rapidly increased, the pitch between two electrodes has been continuously decreased to less than $20~\mu \text{m}$ pitch. Therefore, fine-pitch interconnection technology has become very important in display technology. In our previous research results, anchoring polymer layer (APL) structure was successfully introduced into anisotropic conductive film (ACF) system to form fine pitch interconnection by suppressing the conductive particles movement during the ACF assembly. In general, the agglomerated conductive particles between two electrodes can cause short-circuit problems at ACF assembly. In this paper, the magnetic field was applied to the Ni-coated polymer conductive particles in the polyvinyl fluoride (PVDF) APL structure to disperse the conductive particles uniformly in the xy plane. Then the effects of the magnetic fields on the dispersion of the Ni-coated conductive particles in the PVDF APL structure and the characterization of fine-pitch chip-on-glass (COG) assembly using PVDF APL ACFs with magnetically dispersed conductive particles were investigated. By optimizing the magnetic fields on the PVDF APL structure, 80% dispersed particle rate was successfully obtained. After the ACF bonding process, the conductive particles capture rates and contact resistance properties of magnetically dispersed PVDF APL ACFs, and the PVDF APL ACFs with no magnetic field applied were investigated at 20- $\mu \text{m}$ -pitch COG applications. Both PVDF APL ACFs showed a similar capture rate of conductive particles and electrical insulation property at $20~\mu \text{m}$ pitch. The PVDF APL ACFs with no magnetic field applied showed 100% of insulation property at $20~\mu \text{m}$ , but short circuits at less than pitch. However, for less than 20- $\mu \text{m}$ pitch, only the PVDF APL ACFs with magnetically dispersed conductive particles showed 100% insulation circuit rate down to the 11- $\mu \text{m}$ pitch because the conductive particles were not agglomerated but existed as single particles, resulting in no electrical short between fine-pitch adjacent bumps. As a result, magnetically dispersed PVDF APL ACFs can be used as new ACF materials for ultrafine-pitch interconnection applications without any electrical short.