Platform for Temporary Testing of Hybrid Microsystems at High Frequencies

In this paper, a platform based on the composite-IC concept that is optimized for high-frequency (HF) applications will be presented. Surface-micromachined microsprings are used for temporary connection and testing. This provides the system with an individual compensation of different contact heights due to production tolerances. In addition, self-alignment structures have been added to compensate lateral tolerances. The presented self-alignment structures were designed to compensate rising precision requirements in contrary to commonly used placing machines. Key elements of the HF platform are coplanar waveguides and microsprings that are processed using microelectromechanical-system technologies on alumina ceramic. Microsprings with outer dimensions between 2000 and 125 mum with different beamwidths, beam thicknesses, and beam lengths were designed, simulated, and fabricated. All structures were tested mechanically and electrically. As a further development, spiral microsprings are presented. These combine minimal space requirement with no preferred orientation. Positioning in an individual array is possible. Due to the design and the integration of the spiral microsprings as part of the flip-chip connection, the scattering parameters show excellent HF performance up to frequencies of 9 GHz. The same microsprings could also be used for onboard testing on multichip modules (MCMs). This provides the MCM with cheap and powerful testability and reworkability. This paper covers the mechanical and electrical design, simulation, optimization, production, and characterization of suitable microsprings.