Flexible Stack Package Segmentation for Stress Distribution

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Solution Overview

Problem

Existing flexible stack packages face challenges in reducing the total thickness while maintaining flexibility, as they are prone to damage due to tensile or compressive stress when warped, especially when multiple semiconductor chips are stacked.

Innovation Solution

The design incorporates a stack structure with unit packages that have both fixed and floating areas, where the fixed areas are connected using fixing connectors and adhesive layers, and the floating areas allow for independent movement, using flexible layers to encapsulate chips and distribute stress evenly, creating a mechanical neutral plane to prevent damage during bending.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If multiple semiconductor chips are stacked to reduce total thickness, then the package density is improved, but the flexibility deteriorates due to increased stress during warping

Engineering Contradiction:

Improvetotal thicknessVSAvoidflexibility

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

The stack package is divided into multiple unit packages, each containing a semiconductor chip. This segmentation allows each unit to be independently supported by flexible layers, reducing the cumulative stress effect on the entire stack and maintaining flexibility even with multiple chips.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Flexible layers are introduced between and around the semiconductor chips to provide mechanical support and distribute stress during warping. These flexible films prevent the rigid chips from experiencing excessive tensile or compressive stress, enabling the multi-chip stack to maintain flexibility.

Inventive Principle:

Principle #30Flexible shells and thin films

2Reliability

If the stack package is made thinner to improve flexibility, then the flexibility is improved, but the stress concentration increases causing damage to the chips

Engineering Contradiction:

ImproveflexibilityVSAvoidstress resistance

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

Flexible layers are pre-positioned between the semiconductor chips to act as cushioning elements. When the package is warped, these flexible layers absorb and distribute the mechanical stress before it reaches the chips, preventing stress concentration and potential chip damage.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The package structure combines rigid semiconductor chips with flexible supporting layers to create a composite structure. This composite design allows the rigid chips to maintain their functional integrity while the flexible layers provide stress distribution and damage prevention during warping.

Inventive Principle:

Principle #40Composite materials

3Device complexity

If multiple semiconductor chips are stacked to reduce total thickness, then the device complexity is reduced, but the manufacturing precision requirements increase due to stress management

Engineering Contradiction:

Improvestack structureVSAvoidstress distribution

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The flexible layers are strategically positioned at specific locations between and around the chips where stress concentration is most likely to occur during warping. This localized placement optimizes stress distribution without requiring complex modifications to the entire package structure, maintaining manufacturing feasibility.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS9269657B2Flexible stack packages, electronic systems including the same, and memory cards including the same

Publication Date: 2016.02.23 SK HYNIX INC

AI summary

Flexible stack packages are provided. The flexible stack package includes a first unit package and a second unit package which are sequentially stacked. Each of the first and second unit packages has a fixed area and a floating area. The fixed area of the first unit package is connected and fixed to the fixed area of the second unit package by a fixing part.