From micropackages to MCMs up to 40 GHz for space applications

Alcatel Space Industries has been working in the field of RF hybrids for a long time. This paper presents the evolution of microwave packaging, up to 40 GHz, towards more and more miniaturisation. RF packaging presents challenging trade-offs between electrical performances and manufacturability; the higher the frequency, the more these two parameters are intertwined. In the 80´s, most of the RF hybrids were based on bare transistors associated with thin film substrates and heavy packages. The first important step in the field of miniaturisation was the introduction, at the beginning of the 90´s, of MMICs and micropackages. In addition to the reduction of size, the main objectives were to achieve a high packaging efficiency (ratio between GaAs die and total package surface) and to provide a high performance interconnection system both within the module and to the outside world. Then, another step for miniaturisation was the introduction of mixed LF/MM wave MCM which associated HTCC (High Temperature Cofired Ceramic) with microwave connections through ceramic feedthroughs. This allowed a drastic reduction in volume and weight through the hybridisation of the DC part with the microwave dice. The next evolution could be the use of LTCC to favour the introduction of passives, the flip-chip interconnection to minimise the length of RF connections and/or the use of AlN-Aluminium Nitride-for thermal management. Now, those different technologies could be associated with other miniaturisation concepts adapted to the microwave needs, such as SOC (System-On-a-Chip) or SOP (System-On-a-Package). However, this then involves the optimisation of active device selection, the intelligent partitioning of functions between the active and passive media for the specific subsystem architecture adopted and the co-design of the application