A technique has been developed for the assembly of GaAs MMICs using flip-chip solder bonding. The additional process steps needed to permit solder bonding are compatible with fabrication in the Plessey GaAs MMIC Foundry. Flip-chip bonding allows reproducible, high integrity interconnections to be made in a single assembly operation, while adding the design freedom of mid-chip connections. The key to the success of the technology is the provision of a barrier metallisation layer interposed between the solder and the gold bond pads of the MMIC and MIC substrate circuitry. Demonstrator receiver MMICs were designed, fabricated, assembled and tested. The GaAs chip was designed as unconnected building block circuits and the receiver function generated by interconnection tracks on the MIC substrate. Clearly different microwave operating parameters were derived from the same GaAs chip design by altering the MIC design. Selective receiver operation was demonstrated between 2 and 7 GHz, with up to 20 dB conversion gain.
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