The authors describe three-dimensional electromagnetic field analysis of interconnections in copper-polyimide multichip modules. This analysis is based on the spatial network method, a lattice network model of Maxwell's equation formulated in the time domain by Bergeron's method. Results of simulating reflection and transmission waves at interconnections are presented. Frequency characteristics of the scattering parameter S/sub 21/ are calculated using the fast Fourier transform. The 3-dB down cutoff frequencies of wire-bonded, TAB (tape automated bonding), and FCB (flip-chip bonding) interconnections are respectively 6, 14, and 40 GHz. Those of the interconnection vias are over 200 GHz.<<ETX>>