Resin and flexible metal bumps for chip-on-glass technology

LCDs (Liquid Crystal Displays) are now widely used in various display terminals: as a result, there is great demand for an LCD performance which has such factors as excellent display quality, high resolution and large capacity. In the LCD field, not only device technology but also packaging technology significantly influences display performance. Therefore, it is a most urgent matter to develop a structure and a process interconnecting LCD driver LSIs with hundreds of electrodes to a glass substrate at a fine pitch. For this reason, the authors have developed a novel COG (Chip-on-Glass) interconnection technology, in which an LSI chip like a sticker is electrically and mechanically connected quickly to a glass substrate, using flexible metal bumps formed selectively on electrode pads of an LSI chip and adhesive portions formed by photo-thermosetting resin between electrode pads. To acquire the novel interconnection method, the following technology has been developed: (1) New photo-thermosetting resin which is not thermoplastic, can adhere to a substrate even after being patterned and uses a photolithographic process; (2) Original process, using the photo-thermosetting resin and flexible metal bumps where flexible indium bumps are formed on electrode pads of LSI chip. Adhering portions by photo-thermosetting resin are formed selectively where there are no connecting pads. The LSI chip is mounted and connected to a glass substrate at low temperature(less than 150°C). The LSI chip is electrically and mechanically connected to the glass substrate at a fine pitch; (3) Inspection/repair technique. It is possible to electrically inspect driver LSI chips which have been mounted and precure bonded on the LCD panel, before postcure bonding. If the driver LSI or mounting character is defective, appropriate repair is possible, With this new COG technology, fine pitch, such as 50 μm electrode pads for driver LSIs, can be interconnected to ITO electrode terminals on an LCD panel. The reliability tests on test samples fabricated by the developed COG technology demonstrated good results. This paper describes the process and features of the developed COG technology