Flip chip-bonded GaAs MMICs compatible with foundry manufacture

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 wire-bonded form. All the bonds on a chip were made in a single solder reflow operation, representing a considerable saving in assembly effort.