Flip chip-bonded GaAs MMICs compatible with foundry manufacture

Abstract
A foundry-compatible flip-chip bonding technology has been developed for gallium arsenide monolithic microwave integrated circuits (MMICs). Metallurgical interactions between lead-tin solder and gold-based circuitry were prevented by the inclusion of a pinhole-free metal barrier layer. The solder bonds were extremely reproducible and provided a self-alignment capability at the flip-chip bonding stage. Microwave measurements showed test components to have more uniform characteristics than their wire-bonded counterparts and MMIC amplifiers to have the same behaviour in flip-chip or wirebonded form. All the bonds on a chip were made in a single solder reflow operation, representing a considerable saving in assembly effort.

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