Package-on-Package Interconnects via Stacked Metal Bumps

The patent implements package-on-package architecture where a first semiconductor package is embedded within a second semiconductor package. The first package contains a first substrate with first bumps, while the second package contains a second substrate with second bumps that electrically connect to the first substrate. This nesting approach dramatically increases integration density by stacking functional layers vertically rather than expanding horizontally, achieving higher component density in a smaller form factor.

The invention transitions from planar two-dimensional packaging to three-dimensional stacked packaging. By utilizing the vertical dimension (Z-axis) with multiple stacked packages connected through through-substrate vias and bumps, the system achieves higher integration density without increasing the footprint area. The first substrate is positioned at a first level and the second substrate at a second level, creating a vertical interconnect architecture that exploits the third dimension for enhanced density.

The patent extracts and eliminates parasitic inductance by implementing direct solder bump connections between stacked packages. The bumps provide low-inductance electrical pathways compared to traditional wire bonds or trace connections. By removing intermediate connection structures that introduce parasitic elements, the design achieves lower energy loss and improved high-frequency performance while maintaining high integration density.

The patent introduces under-bump metallization (UBM) structures as intermediary layers between the solder bumps and the substrate traces. These UBM layers serve as transition structures that reduce parasitic inductance and improve electrical connectivity. The UBM provides a low-impedance path for electrical signals, acting as a mediator that minimizes energy loss while enabling reliable bump connections to the underlying circuit traces.

The patent employs preliminary alignment features such as alignment marks, registration holes, or guide structures fabricated on the substrates before the bumping and stacking processes. These pre-formed alignment features enable precise positioning of the first substrate relative to the second substrate during assembly. By establishing alignment references in advance, the system achieves accurate bump-to-pad registration even in multi-layer stacked configurations, ensuring reliable electrical connections.

The patent implements self-aligning bump structures where the bump geometry, material composition, or mechanical properties enable automatic positioning during the bonding process. For example, bumps with specific spherical shapes or materials that exhibit self-centering characteristics can automatically align with corresponding pads on adjacent substrates during reflow or bonding, reducing the need for high-precision external alignment mechanisms and improving yield.