A novel MCM package for RF applications

It has recently become evident (Davis et al, 1998) that there are many important design and performance advantages to be gained by using a flip-chip silicon-on-silicon MCM (multichip module) architecture for RF applications. This paper describes the structure and assembly of a 1.016 GHz GSM MCM transceiver. In this example, an RF transceiver chip is flip-chip mounted on a circuited silicon substrate which, as part of its circuitry, includes embedded capacitors, inductors and resistors. The resulting flip-chip silicon-on-silicon structure, which is called a "tile" and incorporates all of the RF sensitive nodes, is itself inverted and solder connected to the top side circuitry on a double sided FR-4 laminate substrate. This substrate is furnished with bottom side solder balls for surface mount assembly to, for example, an FR-4 PWB motherboard. Tests of the resulting MCM package showed an exceptionally clean RF resonance peak with none of the spurious resonance peaks that were observed with a transceiver chip of the very same design when enclosed in a conventional leaded package and surface mount soldered to a conventional PWB motherboard. This compact packaging architecture allows for the design and manufacture of optimized MCM packages for RF transceivers that can be as thin as the MCM tile alone.