Electrical circuit assemblies

An electrical circuit assembly uses a plurality of stacks upon a generally planar support. Each constituent stack has a plurality of modules having planar substrates extending at right angles to a longitudinal axis of symmetry of the stack. The axis of symmetry is perpendicular to the generally planar support and various electrical interconnections extend between adjacent substrates parallel to this axis. Electrical circuit elements are mounted upon the substrates and the substrates are spaced to facilitate flow of cooling fluid, such as air, between the substrates. Heat conducting fins may be mounted on the substrates. To facilitate flow of cooling fluid, stacks of substrates are staggered or offset from substrates of an adjacent stack. A plurality of the electrical circuit assemblies may be combined together.