Elliptical Redistribution Pad Layout for CTE-Stressed Fan-Out Packages

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Solution Overview

Problem

Integrated fan-out packages face reliability issues due to Coefficient of Thermal Expansion (CTE) mismatch, which causes deformation and stress in the redistribution circuit structure, affecting the yield and reliability of the package.

Innovation Solution

The use of oblong-shaped or elliptical-shaped redistribution pads in the metallization structures, aligned with under bump metallurgies, reduces stress by optimizing the thermal expansion mismatch, enhancing the package's reliability and yield.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If circular redistribution pads are used in the metallization structure, then the manufacturing process is simple, but the polymer stress increases due to CTE mismatch, reducing package reliability

Engineering Contradiction:

Improvepackage reliabilityVSAvoidmetallization structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies asymmetry by changing the redistribution pad shape from circular to oblong or elliptical. This asymmetric geometry is specifically designed to reduce polymer stress caused by CTE mismatch between the molding compound and the semiconductor die. The oblong shape with its elongated dimensions provides a larger area for stress distribution while maintaining alignment with the under bump metallurgy, thereby improving package reliability without significantly complicating the manufacturing process

Inventive Principle:

Principle #4Asymmetry

2Reliability

If the redistribution pad shape is optimized to reduce stress, then package reliability improves, but the manufacturing precision requirements increase

Engineering Contradiction:

Improvepackage reliabilityVSAvoidpad shape precision

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent employs parameter changes by modifying the geometric parameters of the redistribution pad from a circular shape (defined by a single radius parameter) to an oblong or elliptical shape (defined by multiple parameters including length, width, and aspect ratio). This allows for optimization of the pad dimensions to better match the under bump metallurgy and reduce stress concentrations. The specific parameter adjustments enable stress reduction while maintaining manufacturability through standard photolithography processes

Inventive Principle:

Principle #35Parameter changes

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This design reduces polymer stress by approximately 19% compared to circular redistribution pads, improving the reliability and yield of the package structures by mitigating thermal expansion-related issues.

Implementation Method 1

Coefficient of Thermal Expansion (CTE) mismatch, which causes deformation and stress in the redistribution circuit structure

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS11830800B2Metallization structure and package structure

Publication Date: 2023.11.28 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A metallization structure electrically connected to a conductive bump is provided. The metallization structure includes an oblong-shaped or elliptical-shaped redistribution pad, a conductive via disposed on the oblong-shaped or elliptical-shaped redistribution pad, and an under bump metallurgy covering the conductive via, wherein the conductive bump is disposed on the UBM. Furthermore, a package structure including the above-mentioned metallization structures is provided.