Community Research and Development Information Service - CORDIS

Microelectronic screen printing using etched foil screens

Screen printed multilayer circuits with 50 um lines and spaces have been fabricated. The project covered developments of screen, paste and printer to achieve this. Etched foil screens have been developed which are capable of printing 50 um lines and spaces. Screen printing is widely used in the microelectronics industry for fabrication of circuitry. The process is wholly additive (efficient), fast (cost-effective) and well understood (reliable). Other high definition technologies are subtractive and costly. A fundamental limitation to the feature size reduction that can be achieved using screen printing is imposed by the periodic nature of the mesh screen. Once a feature is reduced below 2 mesh counts in size, the mesh wires become dominant in defining edges. In the foil screen, the mesh is replaced by a stainless-steel foil, and mesh openings are produced by etching paste feeder holes. Computer aided design (CAD) software generates a hole pattern to accurately align with every pattern feature. Standard thick film printing equipment and pastes may be used, but optimum registration and resolution will be achieved with the associated advanced printer and paste. Advanced techniques have been developed for the production of sub-micron particle size, high performance thick film fine line printing pastes. A paste based on these methods, in a rheology optimized for etched foil screens has been developed, and printability, bondability and adhesion life testing completed. Advanced printer design has made available print-to-print and layer-to-layer registration within +/- 15 um. This has been achieved by the addition of a high resolution optical alignment system to a highly stable machine base. These development were brought together in the fabrication and test of two different multilayer (5 and 6 conductor layer) multichip module (MCM) circuits. Some of the prints contained over 10 m of tracking at dimensions down to 50 um line and space. This development marks the introduction of a technology set to improve the resolution of thick film screen printing by half an order of magnitude.

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Chris ROBERTSON, (Microelectronics Group Manager)
Tel.: +44-1372-367204
Fax: +44-1372-367134
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