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Graphic element Research > Growth > Research projects > Materials & technologies projects > Unique polymers hold key to low-cost electro/optical integration
Graphic element Unique polymers hold key to low-cost electro/optical integration

A remarkable family of hybrid inorganic-organic materials shows outstanding promise as the basis for volume manufacture of sophisticated electronic and electro/optical devices, using low cost materials and production techniques. The DONDODEM project is bringing the technology much closer to commercial realisation - offering Europe a significant advantage in key markets such as telecommunications, information processing and multimedia. These polymers and production technologies could offer consumers affordable optical 'fibre to the home' solutions, for example for very high speed internet and telecommunications connections and applications.

ORMOCER®s (inorganic-organic polymers, a registered trademark of Fraunhofer-Gesellschaft (FhG), Germany), resulted originally from a Brite-Euram II project on the 'development of new dielectrical and optical materials, testing and comparison with existing polymers and application in multi-chip-modules'. The follow-up DONDODEM project under Brite-Euram 3 involved an enlarged consortium of research institutes and companies involved in the electronics and optical sectors.
ORMOCER®s exhibit a unique blend of dielectric and optical transmission properties, combined with environment-friendly low-temperature processability and the thermal stability to withstand subsequent metallisation and soldering. This makes them ideal for the mass production of multi-chip modules (MCMs) for a wide variety of consumer and professional equipment.

The basic structure of an ORMOCER® comprises a silicon-oxygen network modified by the introduction of chemically cross-linkable organic components. Variation of the inorganic-organic precursors enables the properties of the end product to be tuned precisely to application requirements.

Dissolving of the resin in organic solvents gives a range of low- to high-viscosity lacquers that are easily applied as thin layers onto inexpensive polymeric printed circuit board (PCB) substrates, by industry-standard procedures. After final curing at temperatures as low as 120° to 170°C, they withstand subsequent processes such as wave-soldering at up to 280°C.

Manufacture simplified

The uncured lacquers act as negative photoresists, enabling patterning and development of thin films using conventional photolithographic techniques.

Sequential build-up processing can produce multi-layer substrates or packages with high density circuit patterns that can contain both electrical and optical interconnects and also passivation layers. The free-flowing ORMOCER®s also give better than 95% planarisation (very flat layer surfaces) that facilitate multi-layering and flip-chip mounting. By contrast, competitive materials currently under development require curing temperatures of 250° to 350°C, ruling out the cheaper substrates - while planarisation is much poorer.

For optical waveguides, employed to direct light signals from emitting sources to receiving detectors or fibre-optic cables, two ORMOCER® grades with differing refractive indices are required. One forms the lightguiding core, while the other surrounding layers serve as reflective cladding. However, electrical interconnects can also be formed by metallisation on the same layers - so complete structures can be produced within just two grades and three layers. This simplification enables novel efficient systems solutions and also has strong environmental advantages, mainly due to much higher performance-size ratio but also in terms of reducing process energy consumption and solvent emissions.

At the end of the Brite-Euram II project in 1998, the consortium was already able to demonstrate the world's smallest PentiumTM MCM-L/D and to show an ability to integrate for the first time truly electrical and optical interconnects in the same substrate.

Process being scaled-up

These initial successes attracted major international attention, and encouraged more European partners to join DONDODEM, forming an alliance of leading researchers and industrial players from the electronics and optical sectors. Even such commercially competitive organisations as Ericsson, Motorola and Bosch felt able to join this co-operative research initiative, pooling their separate expertise to the ultimate benefit of all participants.

In the three-year project, which runs until September 2001, the emphasis has moved from materials development and characterisation to the investigation of scalable processes that could put ORMOCER®s onto world markets by 2001.
In Germany, according to the Fraunhofer Institute for Silicate Research (ISC), Heraeus is gearing up to produce larger batches of the lacquers to permit more extensive pilot trials. At the same time, Swedish partner Viasystems is working on a curtain coating process that will enable substrates to be covered at rates of up to 5 m/s.

Another major innovation is the introduction of combined lithographic/reprographic patterning by Germany's Institute for Applied Optics and Precision Engineering (IOF), Friedrich Schiller University and Süss MicroTec. Sweden's ACREO, which recently acquired a state-of-the-art high-resolution mask-aligning system handling up to 25 0.6 x 0.6 m2 panels per hour. A demonstrator module produced by the Swiss Center for Electronics and Microtechnology (CSEM) that bundles four laser emitters, four lenses, diffraction devices and overall protection is another example that illustrates the versatility of the new ORMOCER® materials.

Bull and the Technical University of Berlin have preliminarily proved the efficiency of wire-bonding and flip-chip component application, and Berlin University is now conducting long-term reliability testing.

At the same time, Bosch and Thomson-CSF Detexis are investigating the feasibility of thick-layer coating - up to 150 µm - and patterning which will pave the way for high frequency MCMs and yet more specialised optical and electro-optical applications.

  Strong base for future markets

According to DONDODEM co-ordinator Dr Michael Popall of the ISC, the patented ORMOCER® technology gives Europe one very essential basis to compete in tomorrow's performance and price-driven markets. It will help to reinforce the EU's strong position in mobile communication, while low-cost electro-optical components will hasten the realisation of a future-proof broadband fibre-to-the-home infrastructure. More opportunities will be created for large and small enterprises in applications ranging from laser pointers and readers to high-speed data exchange networks.

Manufacture simplified
Process being scaled-up
Strong base for future markets

Key data

EU-funded research in the New materials & production technologies generic action is set to reduce major differences in the cost of integrating electronic and optical components.

Project: DONDODEM - Development of new dielectric and optical materials and process-technologies for low cost electrical and/or optical packaging and testing of precompetitive demonstrators (BRPR980638)

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