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Epson develops COG mounting tech next-gen LCD

Posted: 03 Sep 2007     Print Version  Bookmark and Share

Keywords:COG mounting tech  LCD panels  bumps 

Seiko Epson Corp. has announced a new type of bump for mounting chips to drive next-generation LCD panels and new chip-on-glass (COG) mounting technology for such panels. Volume production of this mounting technology, which is suitable for the high-definition, high-quality requirements of next-generation LCD panels, will begin this year.

Conventional method
Conventional methods for mounting driver chips on LCD panels have generally involved the use of gold bumps formed by electroplating as electric connection terminals (bumps) and COG mounting using Anisotropic Conductive Film (ACF) over electrodes on a glass panel substrate.

However, as pixel densities increase on next-generation LCD panels, and to archive huge number of interconnections, the connecting terminal pitch requires smaller geometry than ever before, so bumps and transparent electrodes have also been miniaturised. Consequently, it has become difficult to trap the necessary number of electroconductive particles with COG mounting using conventional gold bumps. Since the spaces between bumps have shrunk, electroconductive particles dispersed in the ACF accumulate in such spaces, increasing the risk of short circuits between bumps.

Moreover, because ACF interconnections are formed through the electroconductive particles, when the number of conductive particles that can be trapped and contribute to electrical connection is reduced, connective resistance rises dramatically in high temperatures and humid environments. Thus, such technology has already reached its limits in terms of the connective performance needed for next-generation LCD panels, which demand high definition and high quality.

Espon's solution
To resolve the issues outlined above, Epson has developed what it claims as the first resin core bumps formed from metal wire on a resin layer and COG mounting technology using low-cost non-conductive film (NCF). The following features below make this mounting technology suitable for next-generation LCD panels demanding high definition and high quality:

Seiko Epson's new type of bump for mounting chips drive next-generation LCD panels and new COG mounting technology for such panels.
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Smaller geometry for bump pitch—Compared to conventional gold bumps, resin core bumps enable smaller geometry for bump pitch, achieving major advances in miniaturisation of drive chips for LCD panels.

Greatly enhanced reliability of connection—COG mounting does away with the need for electroconductive particles and is completely free from the risk of short circuits between bumps. As a result, it is possible to achieve finer pitch when mounting. COG mounting using resin core bumps achieves more stable connections due to the elastic deformation of the core resin. Furthermore, since the bump metal wire and LCD panel electrodes are directly connected, and therefore form larger connections, the connective resistance of the bump portion remains stable even in high temperatures and humid environments.

No need for new investment—Since chips with resin core bumps can be mounted on LCD panels using existing COG equipment, there is no need to introduce special equipment for the mounting process, so users of chips featuring this technology will incur no costs for investment in new plant.

No need for gold plating—Since there is no need for the plating process required with conventional gold bumps, it is possible to reduce the volume of chemicals used in processing. This helps to reduce environmental impact.

Production schedule
Epson has completed basic development work on resin core bump technology, and volume production is scheduled to begin this year. Epson will supply semiconductor products featuring this technology and provide total solutions in accordance with customer requirements, including provision of the necessary technology.

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