Electrical circuit assemblies

An electrical circuit assembly comprising a plurality of stacks 10 on a common, at least generally planar, support 10A, each stack having a plurality of substantially identically constructed modules 11, each module including a planar substrate 12, with constituent elements of a circuit thereon, has adjacent pairs of substrates spaced apart, so that a cooling fluid, such as air, can flow therebetween, through each stack, and sequentially through at least two stacks. Members 17 are provided, each, at least partially, holding the modules in their required locations in each stack, and such members may comprise, or include, electrical interconnections between the modules. Heat conducting members, possibly formed with fins, may also be mounted on the substrates, in the path of the cooling fluid, and opposing such heat conducting members within a stack may define passages for the cooling fluid. A plurality of such electrical circuit assemblies may be mounted upon a common, at least generally, planar mother support.