Meaning
Interconnect architectures utilizing miniaturized metallic pillars facilitate the vertical integration of stacked integrated circuits within a single package footprint. These micro bump assemblies provide the physical and electrical links between layers in three dimensional integrated circuits. They enable a much higher density of connections than standard flip chip technologies.
Pillar Composition
Copper pillars topped with a thin layer of solder form the primary structure of the connection. In micro bump assemblies, the copper provides a stable standoff height while the solder ensures a reliable bond. This structure prevents the solder from spreading too far and causing electrical shorts between adjacent pins.
Bonding Pitch
Dimensional constraints dictate the spacing between individual connections to prevent interference. Typical micro bump assemblies operate at a pitch of less than fifty microns. Such tight spacing requires high precision placement equipment and advanced lithography to define the bonding sites.
Intermetallic Growth
Diffusion of atoms between the solder and the pillar creates a transition layer during the bonding process. While some growth is necessary for a strong joint, excessive thickness in micro bump assemblies can lead to brittle failure points. Monitoring this layer is a vital part of qualifying the assembly for long term operation in harsh environments.
