Overview of conductive adhesive interconnection technologies for LCD's

Abstract

In the field of flat panel displays, packaging technology has a significant influence on display performance. The electrical interconnect between the LCD and the LCD driver circuit is an area that needs improvement to achieve finer pitch, easier assembly and greater connection reliability. For LCD driver packaging, the ideal assembly process would possess the following characteristics: low processing cost; reliability suitable to the final application; high-density, fine pitch capability; low product profile; acceptable joint resistance; ease of inspection; and reworkability. The overall trend in LCD driver IC packaging has been to move the driver IC closer to the LCD itself. At present, TAB is the predominant packaging approach for large area LCDs. In most cases, the TAB is directly connected to the ITO traces on the glass using anisotropic conductive adhesive (ACA). In chip-on-glass (COG) technology, the driver LSI chips have moved all the way on to the LCD glass itself. COG is typically done by flip chip, also often with the use of conductive adhesives. ITO traces fan out from the IC to the display area, as well as to the point where a polyimide flexible circuit is connected to the glass substrate to supply power and picture information. COG mounting is currently being used in a number of products, in particular when the pixel density is high.