Simulated and practical behaviour of state-of-the-art MCM via structures

The current trend towards high density packaging in multi-layer MCM structures, combined with high data rate operation, has created a demand for accurate high-frequency models of complex interconnection structures. In this paper we present comparisons of measured and simulated data for via interconnections over the frequency range 2-16 GHz. Theoretical predictions of via performance were obtained using a commercial electromagnetic simulator, based on finite element analysis. Results are presented for a range of via dimensions end geometries and show how via they affect the VSWR of MCM interconnections. Via sizes are commensurate with the small via dimensions obtainable using the new KQ technology from Heraeus. In addition to considering cylindrical and square structures, the work has been extended to the modelling of wedge-shaped via interconnections which often result from modern fabrication processes. Results show how the frequency match, expressed in terms of the return loss, deteriorates as the vis structure departs from the ideal cylindrical shape. The simulations and a measurements have bean extended to develop a circuit model for via structures which provides circuit designers with a precise guide to their behaviour which can be used in circuit design