RDL Pad Orientation in PoP Packages for Corner Stress Relief
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Solution Overview
Problem
In Package-on-Package (PoP) processes, the Redistribution Layers (RDLs) near the corners of packages and device dies experience high stresses, leading to potential cracks and reliability issues due to the conventional distribution of RDL pads.
Innovation Solution
The design incorporates center-facing RDL pads near corners to mitigate stress, with bird-beak directions pointing to the package center, and randomly-pointed RDL pads elsewhere to reduce stress and enhance flexibility in routing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional RDL pad distribution is used, then manufacturing simplicity is maintained, but stress concentration occurs at corner RDLs leading to cracks
Solution Approach 1:
The patent applies different bird-beak direction strategies to different locations: corner RDL pads have bird-beak directions pointing toward the package center to reduce stress concentration, while non-corner RDL pads use random orientations. This localized differentiation improves reliability at stress-prone corners without unnecessarily complicating the overall design.
Solution Approach 2:
The patent introduces asymmetric bird-beak directions in corner RDL pads (pointing toward package center) versus non-corner pads (random directions). This asymmetric configuration specifically addresses the stress concentration problem at corners while maintaining manufacturing feasibility through clear directional guidance.
2Reliability
If corner RDL pads are designed with center-facing bird-beak directions, then stress is reduced at corners, but manufacturing precision requirements increase
Solution Approach 1:
The patent changes the orientation parameter of bird-beak directions based on location: corner pads use center-facing directions while non-corner pads use random orientations. This parameter differentiation reduces stress at corners while maintaining manufacturing feasibility through clear directional specifications rather than requiring extreme precision.
Data Source
AI summary
A package includes a corner, a device die, a plurality of redistribution lines underlying the device die, and a plurality of metal pads electrically coupled to the plurality of redistribution lines. The plurality of metal pads includes a corner metal pad closest to the corner, wherein the corner metal pad is a center-facing pad having a bird-beak direction substantially pointing to a center of the package. The plurality of metal pads further includes a metal pad farther away from the corner than the corner metal pad, wherein the metal pad is a non-center-facing pad having a bird-beak direction pointing away from the center of the package.