Each end user partner in the project has designed one or two demonstrator applications. These were made into etched foil screens, printed and then tested. These applications were as follows
- Lange coupler working at 7-10 GHz and showing comparable high frequency performance to an equivalent thin film device: by Extec Hybrids.
- Tchebycheff cascade filter. The virtually slump free printing enabled by the µ-screen /Heraeus gold ink combination allowed fabrication of devices down to 37µm gap working at 16 GHz: by Extec Hybrids.
- Pressure sensor on steel diaphragm. This is a low cost small size device which will supplant traditional devices and, unlike the latter, does not require an additional fluid medium to operate: by Extec Hybrids.
- Humidity sensor : by Hymec.
- Miniaturised filter circuit : by Hymec.
- MCM interconnect. This application had tracks and gaps down to 50µm and highlighted the need for good housekeeping/cleanliness and ensuring the screen was clear of cleaning solvents. Initial difficulties in obtaining good resolution were resolved by moving to the Heraeus gold: by Alcatel.
- Humidity sensor for low cost, miniaturised industrial applications: by Microhybrid.
- Flip chip on ceramic in silver palladium ink technology - preparation for a new mounting technology for naked chips: by Microhybrid.
- Microwave test circuit as comparison with thin film and photoimageable systems for LTCC. This circuit was by far the most complex made during the project comprising many different fine microwave circuits and also large pad areas. This application was particularly valuable in providing the impetus to develop more sophisticated design tools for screen hole patterning (and thereby providing a useful indicator of the design costs involved in a more advanced circuit), demonstrating the excellent printability obtainable for such a wide range of circuit features and also confirming that the µ-Screen is not currently suitable for printing large continuous pad areas (although lattice ground areas can be printed): by Microtel.
- Delay line - comparison of thick film with thin for high frequency devices where the good line edge and width definition of the µ-screen was tested: by Microtel.
- n Segment display interconnect. Reflectivity of interconnect in displays is a problem. This can be reduced by decreasing the line width used in the interconnection. The number of players used in the design were also reduced leading to increased yield and reduced per substrate cost. All of these objectives were met. An additional benefit was that the increased level of cleanliness introduced to use the µ-Screen produced a dramatic increase in device yields for existing components produced in the same production area: by Menvier Hybrids.
- Space application test circuit: by Alcatel ETCA.
- Fan out to flexible connection to display. This application had along length of 35µm space tracking which ultimately could not be printed with no defects. This provides a useful lower bound for µ-Screen based applications. It was also demonstrated that ball-wedge and wedge-wedge bonding onto to printed tracks down to 40 µm line and space could be achieved with little difficulty: by CIL.
- MCI and ERA have increased the reliability and longevity of the µ-Screen, speed of fabrication and yield and reduced the cost of the process. This is a fundamental to making this technology generally acceptable in the market place.
- ERA has also transferred the screen printing process to all of the end user partners including on-site training.
Heraeus have also measured and modified ink rheologies of their gold ink (previously developed on HIDENCON) and of existing silver based inks as requested by some of the partners.
This project addresses the industrial requirement for new technology to provide low cost, high performance microelectronic interconnect and devices. In order to meet the continual demand for reduction in circuit size, manufacturers are moving from conventional, low cost interconnection methods - especially thick film - to more expensive approaches such as thin film and photoimageing. These require major investment and a complete reorientation of production within a company. For SMEs, this is a technological quantum leap which is impossible to resource. The consortium comprises a group of companies, predominantly SMEs, in the field of microelectronics production. The SME partners have identified a generic, low cost, high density interconnection technology capable of providing a solution to this dilemma based on extending the capabilities of screen printing. Owing to the periodic nature of a conventional mesh screen, there is a fundamental limitation to the minimum size of features that can be screen printed. In production, the industry standard for the minimum printable line width is about 200 mm. In the new approach being adopted here, the mesh element of the screen is replaced with a sheet of thin metal foil. This foil is pre-etched with a pattern of paste feeder holes computer designed to exactly match the print pattern. Consequently, the mesh never interferes with the design pattern, and much higher resolution printing at 50 mm line and space can be obtained. The end user partners in this project have identified a range of highly innovative new applications which can only be achieved through use of the foil screen technology. The applications include: - Microwave telecomms: precision components and tracking will halve production costs by avoiding the need for thinfilm technology and significantly raise yield. - Aerospace: higher densities will enable smaller, lighter packages to be made. Reducing the number of layers by 30 % will reduce costs. - Sensors: fine control of print dimensions will enhance sensor performance and yield. Higher densities will increasing market size by a factor of 10. - MCM/Hybrid: high density multilayer will enable smaller packages and /or fewer layers; precision resistor printing will minimise laser trimming costs. - Environmental monitoring: low cost sensors with improved resolution, reduced size circuitry and higher yield inereased from 70 to 95 %. - Displays: reduced stray reflections using narrow conductors, inreased circuit density and reduced number of layers will cut cost by 20 %. The aim of this project is to research, develop and demonstrate the next generation of low cost, high performance microelectronic devices, and subsequently to enable a clear route for exploitation by European industry. There is significant risk in this approach given fierce and fast moving product innovation from the US and the Pacific Rim nations. These risks, while high, are well defined and it is believed that this project will provide major benefits for the European microelectronics and packaging industry for increasing market share as well as having significant performance, environmental and social benefits. This project provides a major opportunity for downstream innovation, dissemination and exploitation by SMEs by accessing the results of large EU R&D projects.
Funding SchemeCRS - Cooperative research contracts
RG28 7BB Witchurch - Hants
KT22 7SA Leatherhead, Surrey
6136 GL Sittard
SG8 6DN Melbourn
OX16 7RX Banbury