ALN Cofired MCM-C/D

Abstract

A MCM-C/D test cell was designed and fabricated to investigate the compatibility of aluminum nitride with cofired tungsten vias forming a pad/grid array with thin film processing, and the high speed (>2 GHz) electrical performance of deposited TiW-Au / polyimide interconnections and the cofired tungsten vias. The test cell supports a multilayer interconnect structure designed to allow for characterization of signal propagation properties (e.g. impedance, characteristic wavelength, cross-talk) of various striplines, via chains, and through substrate I/O and ground plane perforation. The design parameters relevant to electrical characterization are reported in detail. The polished A/N was found to provide a suitable surface finish (< 5 μin rms) for thin film metallization, however, the cofired tungsten vias maintained a 3–5 micron relief after polishing requiring the use of a polyimide planarization layer. Cross-talk is reported for various stripline configurations on perforated ground planes with 45% and 76% metal area.