Evaluation of a double-layer anisotropic conductive film (ACF) for fine pitch chip-on-glass (COG) interconnection

Anisotropic conductive films (ACFs) consist of conductive particles and adhesive resins and have been extensively used for chip-on-glass (COG) interconnection in FPDs (flat panel displays) such as LCD (liquid crystal display) for the last decades. It is one of the highest density packaging processes at present. However, the need for higher resolution and larger capacity displays is driving the need for finer pitch interconnection. In order to meet these requirements, many approaches were developed by researchers. Since it is difficult to capture enough particles on the small bumps while securing the insulation between the adjoining terminals, currently two types of ACF are widely adopted: an ACF containing conductive particles coated with insulated layer; a double-layer ACF that consists of an ACF layer and a NCF (nonisotropic conductive film) layer. However, both of them have the inevitable limitation. An ACF which has a double-layer structure and the ACF layer consisting of conductive particles coating with insulated layer was investigated in this paper. We carried out the COG experiments with test TC and glass under several different contact areas, another kind of normal single-layer ACF was also adopted which has the higher particle density than the novel ACF for comparing. It was found that the number of particles trapped between the bump and the corresponding pad increased obviously. A thermal cycling test and a high temperature humidity test were also taken, the ACF showed more acceptable contact resistance, and no short was found.