Metallurgical Process
Eutectic wafer bonding creates a rigid metallic joint between silicon microstructures and gold metallization layers at a specific temperature threshold. Micro-sensor fabricators utilize au si eutectic bonding to achieve hermetic cavity encapsulation without organic adhesives, operating at the eutectic composition of nineteen percent silicon and eighty-one percent gold by weight. The phase transition occurs at three hundred sixty-three degrees Celsius, forming a liquid intermediate phase that diffuses into both substrate surfaces and freezes into a crystalline joint upon cooling.
Surface oxides block atomic diffusion, requiring native oxide removal or pre-bonding sputtering steps to ensure uniform wetting across the interface.
Phase Transition
Solid-state interdiffusion at the contact interface drives the formation of the eutectic liquid once local temperatures exceed three hundred sixty-three degrees Celsius. Utilizing au si eutectic bonding guarantees immediate solidification upon cooling without significant volumetric shrinkage.
Interfacial Stress
Thermal expansion differences between gold-silicon alloy joints and bulk silicon substrates introduce residual stresses during cooling. Excess mechanical stress alters sensor output signals by bending sensitive micro-machined beams.
Hermetic Sealing
Gas ingress prevention depends on complete perimeter bonding around the micro-sensor cavity. A verified au si eutectic bonding joint maintains leak rates below standard helium mass spectrometer detection limits.
