Innovative methods for printing multi-layer circuits
Thick film processing has been the major and most efficient process for the production of printed integrated circuits. New technologies like the multichip module (MCM) now require a much higher number of interconnections to be available on the chip. This in turn requires a manufacturing technology for high-density thick film printing that will allow mass production at relatively low costs. A consortium of microelectronic industries and SME's have succeeded in providing a microelectronic screen printing method using etched foil screens. Screen printing for the fabrication of circuitry is a process that is efficient, cost effective and reliable. Miniaturisation using the screen printing technique is limited by the periodic nature of the mesh screen. The technique proposed by the current project replaces the mesh with a stainless steel foil. The mesh openings are produced by etching paste feeder holes. Screen-printed multi-layer circuits with 50 micrometers (μm) lines and spaces have been fabricated. With Computer Aided Design (CAD) the hole pattern is accurately reproduced on the film. The project has also developed paste and printer to achieve the best registration and resolution. The paste developed is especially developed for use with etched foil screens and has excellent printable and bonding capacities as well as a long adhesion life. Advanced printer design allows for print-to-print and layer-to-layer registration within 15μm. These developments overcome the limitations of conventional mesh screen printing for thick film microelectronics. The screen is replaced by a metal foil etched with a pattern of feeder holes. Along with the development of a high precision printing machine and an ultra fine line printing paste, a system for printing 50μm line and space thick film features is now tested, available for demonstration and protected by patents. The system was used successfully for the production of two different multi-layer multichip module circuits. The market for multi-layer multichip modules is projected to be roughly 1 billion ECU per annum. The above-described method of production is estimated to address at least 75% of this market alone.
