Metallic Alloy Seal Bonding

Metallic alloy bonding uses an intermediate metal layer to solidly join two or more stacked components. Although metallic alloy bonding comprises outstanding characteristics, it is often considered difficult to handle this technology on wafer-level due to limitations regarding wafer topography, intrinsic stress, and flow control of surplus metal melt. The aim of this chapter is to indicate solutions to those shortcomings. The technology of metal seal bonding includes solder and eutectic bonding, thermo-compression bonding, solid diffusion bonding, and active metal bonding. Wafer bonding with soft solder is a very fast process. During the eutectic wafer bonding, an eutectic alloy composition is generated, forming the seal. Transient liquid phase TLP bonding, also referred to as solid liquid interdiffusion SLID bonding, creates a metallurgical seal by forming a thin liquid phase of one low melting component of the intermediate layer system. Diffusion bonding generates a continuous metallurgical bond between two soft electroplated metals by solid state diffusion without forming a liquid phase. A dedicated design and technology setup is needed for a high-quality and reliable metallic bond. Many aspects may influence the selection of a specific bond process. The final seal ring design is a trade-off between process integration and compatibility, restrictions to subsequent processing, stress and adhesion properties, costs, and environmental aspects.