Integration Techniques for MMICs and Chip Devices in LTCC Multichip Modules for Radio Frequencies

One of the goals of the investigations of the two public R&D projects 4M [1] and RAMP [2] is to find out the advantages and limitations of the multilayer LTCC technology in radio frequency applications. In the first steps the material properties have been determined followed by the investigation of different waveguides and passive structures like transitions, feedthroughs and resonators [3,4,5]. In the next step the integration of monolithic microwave integrated circuits (MMIC) and single chip devices has been tested in different configurations. The basic method is to mount a MMIC on the top layer of the LTCC and connect the RF and DC ports with wire bonds to the circuitry of the carrier substrate. An improved electrical performance can be achieved by embedding a chip into a cavity. This will reduce the length and consequently the parasitics of the bond wire. An other advantage could be the reduction of the total substrate thickness for a better heat dissipation of power applications. MMICs on GaAs are expensive and often have a long delivery time. A promising alternative is to design an RF circuit on the LTCC substrate by using single chip devices, which can be mounted in flip-chip technology on the top layer