Fan-Out Package Pad Layout for Thermal Cycle Reliability
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Solution Overview
Problem
Conventional Package-on-Package (PoP) processes face challenges in the reliability of electrical connectors, particularly in thermal cycles, due to the distribution and shape of solder and non-solder metal pads, which affect the integration and stability of packages.
Innovation Solution
The design incorporates centripetal elongated metal pads at package corners and non-elongated pads elsewhere, with specific distribution based on a neutral-stress point, to enhance thermal reliability by optimizing the layout of metal pads and redistribution lines within the package structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional PoP process with standard metal pad distribution is used, then manufacturing is simple, but thermal cycle reliability is poor (574-604 cycles)
Solution Approach 1:
The patent applies local quality by differentiating metal pad shapes based on their location relative to the neutral-stress point. Corners and regions farther from the neutral-stress point use elongated pads oriented radially outward, while regions closer to the neutral-stress point use non-elongated pads. This localized differentiation optimizes stress distribution in high-stress areas without unnecessarily complicating low-stress areas, achieving improved thermal cycle reliability (769 cycles) while maintaining reasonable manufacturing complexity.
2Reliability
If metal pads are made elongated to improve stress distribution, then thermal reliability improves, but manufacturing precision requirements increase
Solution Approach 1:
The patent employs asymmetry by orienting elongated metal pads radially outward from the neutral-stress point rather than using uniform symmetric shapes. This asymmetric configuration naturally directs stress away from critical regions during thermal cycling. The radial orientation pattern, while asymmetric, follows a systematic geometric rule that simplifies manufacturing guidance compared to arbitrary asymmetric shapes, thus balancing reliability improvement with manufacturability.
3Strength
If centripetal elongated pads are used at corners, then structural integrity improves, but device complexity increases
Solution Approach 1:
The patent segments the metal pad array into distinct zones based on distance from the neutral-stress point. Corner regions and outer regions use elongated pads for enhanced structural integrity, while inner regions use non-elongated pads. This segmentation allows concentrated reinforcement where stress is highest without applying the same complexity throughout the entire array, thus improving structural integrity while controlling overall device complexity.
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 non-solder electrical connectors underlying and electrically coupled to the plurality of redistribution lines. The plurality of non-solder electrical connectors includes a corner electrical connector. The corner electrical connector is elongated. An electrical connector is farther away from the corner than the corner electrical connector, wherein the electrical connector is non-elongated.