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
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.
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.
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.