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Epson Develops World’s First Resin Core Bump COG Mounting Technology for Next-Generation LCD Panels


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Seiko Epson Corporation (“Epson”) today announced it has developed a new type of bump for mounting chips to drive next-generation LCD panels and new Chip on Glass (COG) mounting technology*1 for such panels. Volume production of this mounting technology, which is ideal for the high-definition, high-quality requirements of next-generation LCD panels, will begin this fiscal year. Details of the new technology are to be announced at the 17th Microelectronics Symposium (MES 2007) hosted by the Japan Institute of Electronics Packaging and at the 40th International Symposium on Microelectronics hosted by the International Microelectronics and Packaging Society (IMAPS 2007).

Conventional gold bumps and COG mounting

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)*2 over electrodes on a glass panel substrate. However, as pixel densities increase on next-generation LCD panels, in order to be able to archive huge number of interconnections, the connecting terminal pitch requires smaller geometry than ever before, so bumps and transparent electrodes*3 have also been miniaturized. 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.

World’s first*4 COG mounting using resin core bumps

To resolve the issues outlined above, Epson has developed the world’s first resin core bumps formed from metal wire on a resin layer and COG mounting technology using low-cost non-conductive film (NCF)*5. The features listed below make this mounting technology ideal for next-generation LCD panels demanding high definition and high quality.

(1) Smaller geometry for bump pitch
Compared to conventional gold bumps, resin core bumps enable smaller geometry for bump pitch, achieving major advances in miniaturization of drive chips for LCD panels.

(2) 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.

(3) 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.

(4) 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 fiscal year. Epson will supply semiconductor products featuring this technology and provide total solutions in accordance with customer requirements, including provision of the necessary technology.

Seiko Epson Corporation (“Epson”) today announced it has developed a new type of bump for mounting chips to drive next-generation LCD panels and new Chip on Glass (COG) mounting technology*1 for such panels. Volume production of this mounting technology, which is ideal for the high-definition, high-quality requirements of next-generation LCD panels, will begin this fiscal year. Details of the new technology are to be announced at the 17th Microelectronics Symposium (MES 2007) hosted by the Japan Institute of Electronics Packaging and at the 40th International Symposium on Microelectronics hosted by the International Microelectronics and Packaging Society (IMAPS 2007).

Conventional gold bumps and COG mounting

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)*2 over electrodes on a glass panel substrate. However, as pixel densities increase on next-generation LCD panels, in order to be able to archive huge number of interconnections, the connecting terminal pitch requires smaller geometry than ever before, so bumps and transparent electrodes*3 have also been miniaturized. 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.

World’s first*4 COG mounting using resin core bumps

To resolve the issues outlined above, Epson has developed the world’s first resin core bumps formed from metal wire on a resin layer and COG mounting technology using low-cost non-conductive film (NCF)*5. The features listed below make this mounting technology ideal for next-generation LCD panels demanding high definition and high quality.

(1) Smaller geometry for bump pitch
Compared to conventional gold bumps, resin core bumps enable smaller geometry for bump pitch, achieving major advances in miniaturization of drive chips for LCD panels.

(2) 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.

(3) 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.

(4) 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 fiscal year. Epson will supply semiconductor products featuring this technology and provide total solutions in accordance with customer requirements, including provision of the necessary technology.

*1: Technology for mounting semiconductor chips directly on glass substrates; used for applications such as mounting driver chips on liquid crystal displays.
*2: Made by dispersing microscopic, conductive particles throughout a non conductive adhesive film; used for high density interconnects such as bonding FPC (flexible substrate) to LCD panels (glass substrate) or printed circuit boards.
*3: An electrode that drives an LCD display. A thin film is formed on a glass substrate using a conductive and optically transparent substance.
*4: According to data available to Epson.
*5: An adhesive film used to bond the electrode plane of a semiconductor chip to a circuit board. Unlike ACF, this film does not contain conductive particles.



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