Conductive Pillars for Stacked Semiconductor Package Interconnects
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Solution Overview
Problem
Conventional stacked semiconductor packages face electrical connection issues when the distance between neighboring solder balls decreases, as the reduced diameter solder balls may not properly connect the top package to the bottom package due to insufficient thickness of the die and molding compound.
Innovation Solution
The implementation of conductive pillars on the substrate pads, which protrude from the solder mask layer, allowing for a finer pitch and improved electrical connection between the top and bottom packages without the need for reduced solder ball diameters, and preventing solder bridges and warpage during reflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the distance between neighboring solder balls decreases, then the pitch between packages is reduced, but the diameter of each solder ball must also decrease, causing insufficient thickness to accommodate the reduced diameter solder balls and preventing proper electrical connection
Solution Approach 1:
The patent introduces conductive pillars that protrude vertically from the substrate surface, transitioning from a planar two-dimensional solder ball arrangement to a three-dimensional structure. This vertical dimension allows the conductive pillars to extend through the die and molding compound, establishing electrical connections without requiring the solder balls to be smaller, thus resolving the contradiction between reduced pitch and maintained solder ball diameter.
Solution Approach 2:
The conductive pillars serve as intermediary elements between the substrate pads and the solder balls. These pillars extend through the intermediate layers (die and molding compound) to provide a conductive path, allowing the solder balls to maintain their original diameter while still achieving electrical connection at reduced pitch distances.
2Productivity
If the diameter of solder balls is reduced to accommodate smaller pitch, then the pitch between packages is reduced, but the thickness of die and molding compound cannot be sufficiently thinned, causing connection failure
Solution Approach 1:
By adding the vertical dimension with protruding conductive pillars, the patent creates a three-dimensional connection path that spans the fixed thickness of the die and molding compound. This allows reduced pitch without requiring thinning of these layers, as the pillars extend vertically to bridge the gap.
Solution Approach 2:
The conductive pillars are formed in advance on the substrate pads before packaging. This preliminary action ensures that the conductive pathways are already in place and extend to the necessary height, so when the package is assembled with reduced pitch, the connections are already established without needing to modify the thickness of the die or molding compound.
3Reliability
If conductive pillars protrude from the solder mask layer, then electrical connection is improved, but solder bridges and warpage may occur during reflow
Solution Approach 1:
The patent applies different properties to different regions: the conductive pillars have localized conductivity where needed for electrical connection, while the solder mask layer maintains its insulating properties in surrounding areas. This local differentiation allows electrical connection through the pillars while preventing solder bridges in other regions, and the controlled geometry of pillars minimizes warpage during reflow.
Data Source
AI summary
The present stacked semiconductor packages include a bottom package and a top package. The bottom package includes a substrate, a solder mask layer, a plurality of conductive pillars and a die electrically connected to the substrate. The solder mask layer has a plurality of openings exposing a plurality of pads on the substrate. The conductive pillars are disposed on at least a portion of the pads, and protrude from the solder mask layer.