There has been known a hybrid integrated circuit comprising a multilayer printed circuit board with a flexible planar electrically insulating laminate having an electrically conductive array for connecting to electrical conductor terminals on circuit or component packages or carriers, interconnections for the array being by electrical conductor elements at one or more planes within the laminate. The flexible laminate has holes provided where the packages or carriers are to be secured. A separate rigid metallic heat sinking or spreading member is applied such that protruding thermally conducting metallic pillars thereon pass through the holes in the laminate to contact the packages or carriers. One or more further rigid members, which may also be of thermally conducting material, may be applied to the top of the packages or carriers, clips being arranged to secure the pillars in contact with the packages or carriers. The flexibility of the laminate allows concentration of thermal expansion mismatch between the laminate and the packages or carriers. The laminate is also able to flex or bend in regions between the packages or carriers to optimise contact between the pillars and the packages or carriers and to minimise risk of detachment of the latter from the board. [See GB Patent No. 2 129 223, H 05K 1/18, 1984].
Main disadvantages of that design reside in the complexity of using as modular circuit components, package-free semiconductor devices, for example transistors in the form of crystals, and also in unsatisfactory electric characteristics in the light of providing a required level of output power.
The closest prior art has been disclosed in a high-power microwave hybrid integrated circuit comprising package-free semiconductor devices with contact pads, a dielectric substrate containing holes and a topological pattern on its front side and a shielding metallization on its opposite side, a metallic header with projections adjoining the shielding metallization of the dielectric substrate and passing through the holes thereof, said semiconductor devices being mounted on the projections of the header such that their surfaces with contact pads flush level with a front side of the dielectric substrate, a part of said contact pads being connected to the topological pattern of the metallization and a part thereof being connected to the projections of the header. [See the Journal of "Electronics", Series 1: "Microwave Equipment", Issue No. 1(467), 1996]. In this case, a metallic header is fabricated of copper-molybdenum pseudoalloys to obtain dielectric substrate--metallic header seals which are relatively consistent by a thermal coefficient of linear expansion (TCLE) [hereinafter referred to as "TCLE-consistent"].
However, the proposed design can not be applied when providing miniature modules of an enhanced microwave power level because a proper heat sinking from package-free semiconductor devices is not provided for and a reliable contact of the projections with the shielding metallization of the dielectric substrate is not properly ensured.