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Graphic element Research > Growth > Research projects > Previous projects > Industrial Processes > New adhesives make LCDs smaller and more versatile
Graphic element New adhesives make LCDs smaller and more versatile
     
 
Perhaps the most relentless trend in the electronics and telecommunications industries today is the movement towards smaller, thinner and faster devices. At the same time consumers are demanding increased user friendliness, functionality and power, and all of this at lower prices. Technologies which can answer these needs are increasingly in demand. Liquid Crystal Displays (LCDs) are a case in point. LCDs are thin, lightweight and versatile and are becoming increasingly prevalent, as seen in mobile phones, multimedia terminals and notebook computers. About 90 percent of the LCDs supplied to Europe are produced by Japanese companies, and getting out from under Japanese domination was an important goal for the MIFAD project in its search for a cheaper and better LCD using advanced interconnection technology.
 

The main objective of the MIFAD project was to develop improved and more competitive assembly techniques for high-resolution displays using special electrically conductive adhesive pastes and other mounting techniques.
Research focussed on a group of materials known as Anisotropic Conductive Adhesives or ACAs. These pastes contain small metallic particles enabling them to conduct electricity. They can therefore replace the lead used in conventional soldering techniques. Unlike soldered lead, ACAs adhere to glass, so they can be used to mount computer chips and other miniaturised electronic components directly on glass displays or flexible substrates.
First, a definition of the required functional specifications of high density ACAs was undertaken, as well as an evaluation of US and Japanese-produced ACAs already on the market. New ACAs were then developed in accordance with the new specifications.

Application in LCD assembly

With the new adhesives in hand, three assembly techniques were developed and explored:

1. Chip-On-Flex (COF) technology: the LCD driver chips were mounted on a fine pitch (200µm) flex print using die and wire bonding. Flex print is a thin flexible printed circuit material used to feed signals into the hundreds of display segments . The fine pitch flex print is connected to the glass substrate using ACAs.

2. Chip-On-Glass (COG) techniques: here, the driver chips were mounted directly onto the display substrates, using die bonding, wire bonding and glob-top technologies. A coarse pitch flexible circuit was connected to the LCD glass using ACAs.

3. Tape Automated Bonding (TAB) technology : TAB packaged LCD driver chips were made by bonding each chip contact pad to a Au coated Cu lead of a flexible TAB tap (ILB, inner lead bonding). The Cu/Au conductors on the TAB package were connected directly to the conductors on the display substrate using ACAs. This resulted in a very compact and reliable assembly.

All of these techniques represent new developments in LCD assembly technology. The use of ACAs in place of traditional soldering processes and the mounting of chips directly onto glass or flexible printed circuits means a reduction in the amounts of materials used and allows further minimisation of the size of the LCDs. This in turn will mean smaller, lighter weight mobile phones, multimedia terminals, and notebook and handheld computers.
In terms of environmental performance, in addition to material savings whenever smaller products can take the place of larger ones, the use of ACA techniques eliminates the need for traditional soldering processes and the associated high amounts of lead.

Competition/Exploitation

Project partners Alcatel and Thomson-CSF (formerly Dassault Electronique) are now marketing the new systems for mobile phones and computer terminals. Total sales have been estimated at 66 million euro over the first five years from the start of commercial exploitation. Other potential applications are seen in the automotive industry, where compact flat panel displays can easily be incorporated into dashboards and other equipment.
Dicryl in Spain, the only SME partner, has already initiated sales of circuits on flexible boards (COFs) and expects a total gain of about 40 million euro by 2002. This represents an increase in the company's total turnover of 12 to 15 percent per year. Other partners are investing in expanding production and a follow-up Brite-Euram project is also underway.
The project has also had an impact of employment among the partners. Dicryl has added 30 new positions and Thomson-CSF and Heraeus, the ACA developer, have together created 15 new jobs.

Success

The success of the MIFAD project has been attributed to a high degree of co-ordination and co-operation among the partners. All participants, including suppliers, large manufacturers and end users, were able to incorporate the project into their own coherent business strategies. Most of the partners are now continuing their co-operation in another related Brite-Euram project, although it is now felt that further external support for the exploitation of the existing results is unnecessary.
With similar technologies currently under development in Japan and the United States, this European initiative appears to have arrived just in time to curb the continued domination by foreign companies in this rapidly expanding manufacturing sector.

Cordis RCN: 6632
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