Challenges in the reliability study of chip-on-glass (COG) technology for mobile display applications

This paper reviews the current development of COG technology for display applications, with the emphasis on the challenges in the reliability study. It shows that delamination and Indium-tin-oxide (ITO) corrosion are two major concerns faced by the industry. The former is typically caused by moisture in combination with high temperature. Optimization of the COG bonding process to minimize the warpage appears to be the only practical method to reduce the risk. Experimental and analytic tools are urgently needed to characterize the behaviour of such delamination in user environment to assist the interconnect design. ITO corrosion is typically caused by contamination, moisture, and ionic impurities in ACF or on the glass surface. Smaller pitch, higher electrical potential and temperature accelerate the corrosion process. In order to reduce testing time to validate the robustness of the display, acceleration techniques need to be established to rapidly induce the corrosion failure. It is concluded that further reduction of the pitches to be less than 35 um in COG technology requires a major breakthrough in ACF material and careful reliability design.