Phase Transition
An alloy system with a specific minimum melting point provides a stable bonding medium for wafer-level packaging of micro-electromechanical systems. The aluminum-germanium eutectic composition occurs at approximately twenty-eight percent germanium by weight, which is the point where the mixture melts at a uniform temperature. This metal system is used in microelectronics to form hermetic seals.
Bonding Temperature
The lowest liquidus temperature of this binary alloy allows bonding to occur at temperatures below four hundred degrees Celsius. Utilizing the aluminum-germanium eutectic allows manufacturers to complete wafer bonding without damaging temperature-sensitive CMOS circuits that are integrated on the same silicon. The liquid phase arises quickly during the thermal cycle and creates a highly uniform bond line.
Interfacial Reaction
Chemical diffusion during the bonding process creates a rugged joint with high mechanical strength. During the bonding cycle, the liquid alloy dissolves surface oxides and wets the silicon or metal layers. This action promotes an intimate atomic connection across the entire wafer interface.
Reliability Characteristic
Thermal and mechanical properties of this alloy prevent hermetic seal failure during subsequent assembly steps. The aluminum-germanium eutectic demonstrates excellent resistance to thermal fatigue and maintains its hermetic integrity under extreme environmental testing. This high-density joint blocks moisture and gas ingress, which extends the operational life of the enclosed sensor.
