Packages for multichip modules in military airborne applications must hava some fundamental characteristics: high thermal conductivity, low density, good mechanical properties and a coefficient of thermal expansion nearly equal to that of the microelectronic substrate installed in the package. In many cases, the substrate is alumina with a CTE of 6.5 ppm/°C. Materials such as aluminium, titanium or Kovar fulfil only part of the above requirements. This is critical when large packages are used, such as in electronic warfare systems where modules include wideband RF circuits with large alumina substrates next to dense digital circuits. The solution is then aluminium/ silicon carbide (Al/SiC). The aim of the paper is to present the development and qualification of large packages combining both RF and digital circuitry. The size taken into account in the study is 220 × 220 mm: it covers most of the electronic needs in terms of surface. Various aspects have been analysed from the perspective of the package manufacturer and the end‐user. The interest of Al/SiC is shown by a thermal analysis of a conduction cooled module with different core materials: the reduction in temperature gradient, which for some components reaches 20° C, has a strong effect on the module reliability. The different technological choices, for a first type of packages, are described: an Al/SiC baseplate with an iron‐nickel alloy for the ring and the lid, brazed feedthroughs (within the Al/SiC baseplate) and connectors, surface treatment, ring brazing material, lid welding technique. A second type of packages is also presented: the main difference lies in the interconnections. RF ceramic (HTCC) inserts are introduced in the ring frame. Various RF measurements show the interest of the different package technologies, especially the ceramic inserts with very good results up to 20 GHz.
Lefeuvre, A., Caplot, M., Stranieri, C. and Massiot, P. (1996), "Large AI/SiC Baseplate Packages for Digital and Microwave Applications", Microelectronics International, Vol. 13 No. 1, pp. 26-30. https://doi.org/10.1108/13565369610800151Download as .RIS
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