Particle on Bump (POB) technique for ultra-fine pitch chip on glass (COG) applications

Chip on glass (COG) technology is widely used in liquid crystal display (LCD) modules for connecting driver ICs to the displays especially for small size panels. The most common COG technology currently used in display applications is based on anisotropic conductive films (ACF). As the increasing demand in higher resolution and cost reduction, the bump pitch of the driver ICs becomes finer and finer. The current ACF based COG technology is confronted with two issues: one is the increase of the contact resistance; the other is the increase of the chance of forming shorts. A new approach for ultra-fine pitch chip on glass (COG) bonding, which is named "Particle on Bump (POB)" technology, is described in this paper. The main idea of this technique is to have conductive particles only at the locations where we need them. To achieve this, the conductive particles are first fixed on the bumps of a driver IC by inter-metallic connection. Secondly, the driver IC is assembled on the glass,substrate of an LCD panel with an adhesive by thermal press. The new method yields superior interconnection properties including fine pitch, low contact resistance, and no short. The process development and the feasibility study are described. The electrical and mechanical properties of samples prepared according to the method and the preliminary results of reliability tests are reported.