RF packaging for space applications: from micropackage to SOP - "System on a package"

Alcatel Space 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. An important step in the field of miniaturisation was the use, beginning of 90's, of MMICs based on GaAs Gallium Arsenide - and micropackages, following by the introduction of mixed LF/MMwave MCM. The next evolution is the use of flip-chip to minimise the length of PF connections. In term of bonding reliability, the results give values over more than five times the limits from the standards, even after 500 thermal cycles. From an electrical point of view, the RF measurements made after flip-chip bonding are close to the wafer level measurements, with a shift on gain less than 1 dB on all the frequency range. The association of power flip-chip which high thermal conductive substrates like AlN - Aluminium Nitride - could give at least 40% reduction in the Rth for an amplifier with MMIC mounted flip-chip with emitter bumps. The glob-top technology is not yet used for higher frequencies (i.e. some or some tens of GHz). However, the results presented in this paper show that glob-top is compatible with GaAs MMICs working up to 12 GHz. With some specific design rules, the right encapsulant and the associated processes, there are little degradations of the electrical performances of a Low Level Amplifier working at 10.7 - 12.7 GHz. This has been also checked after thermal cycles. 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 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. (C) 2001 Elsevier Science Ltd. All rights reserved.