PoP Corner Pad Geometry for Thermal Cycling Reliability
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Solution Overview
Problem
Existing Package-on-Package (PoP) processes face reliability issues due to stress concentrations at the solder joints, particularly at the corners of the package, leading to premature failure during thermal cycling.
Innovation Solution
The design incorporates centripetal elongated openings in the package structure, with elongated openings positioned to alleviate stress concentrations by aligning their longer axes towards the neutral-stress point, and corresponding elongated metal pads to enhance bonding strength and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional square or circular solder pads are used in PoP packages, then manufacturing is simple, but stress concentrations occur at the corners leading to reliability failures during thermal cycling
Solution Approach 1:
The patent applies asymmetry by changing the pad shape from conventional square or circular symmetric shapes to D-shaped asymmetric pads. The D-shape features a flat side positioned away from the package corner and a curved side toward the corner, creating an asymmetric geometry that eliminates corner stress concentrations while maintaining manufacturing feasibility through standard photolithography processes.
Solution Approach 2:
The patent applies local quality by modifying only the critical corner regions where stress concentrations occur. The D-shaped pad design specifically addresses the corner areas with its curved geometry, while the overall pad structure remains compatible with existing manufacturing processes. This localized geometric modification targets the specific problem area without requiring complete redesign of the entire packaging system.
2Strength
If larger solder pads are used to increase bonding area, then bonding strength improves, but stress concentrations at corners increase leading to earlier failure
Solution Approach 1:
The D-shaped pad design uses asymmetry to redistribute stress away from corner regions. The curved geometry of the D-shape eliminates sharp corners where stress would concentrate, while the flat side provides a large bonding area for strong solder attachment. This asymmetric shape allows the pad to maintain large bonding area for strength while avoiding the corner stress concentrations that cause reliability failures.
Solution Approach 2:
The patent applies parameter changes by modifying the geometric parameters of the solder pads from conventional shapes to D-shapes. This geometric parameter change alters the stress distribution pattern, reducing peak stress values at corners while maintaining adequate bonding area. The parameter modification achieves both improved strength through adequate bonding area and improved reliability through reduced stress concentrations.
3Reliability
If additional stress relief features are added to the package structure, then reliability improves, but manufacturing complexity and process steps increase
Solution Approach 1:
The patent applies local quality by implementing stress relief through localized geometric modification of the solder pads themselves, rather than adding separate stress relief features. The D-shaped pad geometry inherently provides stress relief at the corners through its curved design, eliminating the need for additional complex stress relief structures. This localized approach maintains manufacturing simplicity while achieving reliability improvement.
Solution Approach 2:
The D-shaped pad design serves multiple functions simultaneously: it provides the bonding interface for solder attachment, acts as a stress relief feature through its curved geometry, and defines the solder paste application area. By combining these functions into a single geometric design element, the patent avoids adding separate stress relief features that would increase manufacturing complexity, achieving multi-functionality without additional process steps.
Data Source
AI summary
A package includes a corner, a device die, a molding material molding the device die therein, and a plurality of bonding features. The plurality of bonding features includes a corner bonding feature at the corner, wherein the corner bonding feature is elongated. The plurality of bonding features further includes an additional bonding feature, which is non-elongated.