Re-Etched RDL Seed Layers for Fine-Pitch InFO Packaging

The patent transitions from planar 2D packaging to 3D vertical packaging by forming stacked die structures with multiple layers of I/O pads connected through vertical vias. This dimensional change allows significantly higher I/O pad density without reducing the pitch on individual die surfaces, thereby avoiding solder bridges while increasing the quantity of I/O pads.

The patent implements nested packaging by stacking multiple die layers vertically, where each die is positioned over the previous layer and connected through alignment marks and vias. This nesting approach enables multiple I/O interfaces to be packed in a compact vertical space, dramatically increasing I/O pad density without compromising pitch control on each die layer.

The etching process is segmented into distinct selective steps: first etching through the first dielectric layer to form vias, then etching through the second dielectric layer to form additional vias and trenches. This segmentation allows precise control over the formation of RDL structures at different vertical levels, enabling complex 3D interconnects while managing process complexity through systematic step-by-step fabrication.

The patent applies local quality by using different etching selectivities for different dielectric layers and regions. The first and second dielectric layers have different etching rates, allowing selective removal of material in specific areas to form vias, trenches, and RDL structures. This localized control enables precise formation of interconnect structures without requiring excessive process steps.

The patent applies preliminary anti-action by forming a mandrel structure before depositing the RDL material. The mandrel serves as a template that defines the precise geometry of the RDL, preventing undercut formation during subsequent etching or deposition processes. This preliminary structure ensures that fine-pitch RDLs maintain their intended dimensions and profiles, thereby improving reliability while keeping the manufacturing process manageable.

The patent performs preliminary actions by first forming vias and trenches through selective etching, then filling these structures with conductive material to form RDLs. This sequence of preliminary actions ensures that the RDLs are formed in precisely defined locations with controlled dimensions, preventing undercut issues and ensuring reliability of fine-pitch interconnects before subsequent packaging steps are performed.