Stepped Pad Structure in Stacked Chips for Stable Solder Joints
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Solution Overview
Problem
There is a challenge in developing semiconductor packages that are both high-performance and slim, while also achieving multi-functionality, high capacity, and miniaturization.
Innovation Solution
The semiconductor package includes a stacked configuration of multiple semiconductor chips with pads having a stepped structure, where the first pad on the top surface of the second semiconductor chip has a first portion and a second portion protruding vertically, and a solder ball surrounds the sidewall of the second portion between the first and second pads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple semiconductor chips are integrated into one package to achieve high capacity and miniaturization, then the functionality and capacity of the package are improved, but the complexity of the package structure increases
Solution Approach 1:
Multiple semiconductor chips are stacked vertically in a nested configuration, with each chip containing pads that extend through or between chips. This nesting approach allows multiple functional units to be integrated in a compact vertical arrangement, achieving high capacity and multi-functionality while controlling package footprint.
Solution Approach 2:
The pad structures extend in the vertical dimension rather than only horizontal planes. Pads protrude from chip surfaces and extend through intermediate spaces, utilizing the vertical dimension to create electrical connections between stacked chips without requiring larger horizontal spacing.
2Length of stationary object
If the thickness of semiconductor packages is decreased to make devices slimmer, then the profile of electronic devices is improved, but the space for electrical connections and signal transmission is reduced
Solution Approach 1:
Electrical connections are established by extending pads vertically through the package thickness rather than requiring long horizontal traces. This vertical routing through vias and protruding pads reduces the horizontal distance signals must travel while maintaining connection integrity across thin package profiles.
Solution Approach 2:
The electrical connection path is segmented into discrete vertical elements (protruding pads, solder balls, vias) distributed through the package thickness. This segmentation allows signals to transition between chips at multiple intermediate points rather than requiring single long-distance connections, improving signal integrity in thin packages.
3Reliability
If pads are designed with stepped structure to improve solder ball stability, then the reliability of connections is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The pad structure features localized geometric variations with different widths at different heights (stepped configuration). The upper portion has a narrower width while the lower portion has a wider base, creating a stepped profile that mechanically stabilizes solder balls while using standard fabrication techniques.
Data Source
AI summary
A semiconductor package including a first semiconductor chip, a second semiconductor chip disposed on the first semiconductor chip, and a third semiconductor chip disposed on the second semiconductor chip. A first pad is disposed on a top surface of the second semiconductor chip, and includes a first portion and a second portion protruding in a vertical direction from the first portion. A width of the first portion in a first horizontal direction is greater than a width of the second portion in the first horizontal direction. A second pad is disposed on a bottom surface of the third semiconductor chip facing the top surface of the second semiconductor chip, and a solder ball is disposed as surrounding a sidewall of the second portion of the first pad between the first pad and the second pad.