Through-Substrate Metal Posts for 3D Die Stacking

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Solution Overview

Problem

Conventional 3D device packaging techniques face challenges with precise alignment of copper pillars, leading to non-wetting issues and increased footprint, requiring additional non-electrically active pillars and underfill, which complicates the stacking process and increases the package size.

Innovation Solution

The through-substrate pillar bonding technique involves forming metal pillars or stud bumps using electroplating or wire bonding processes, allowing for precise alignment and contact between dice, reducing the need for underfill and dam structures by inserting metal posts or stud bumps through access holes in the substrate, facilitating a more compact stack.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If copper pillar bumps are used for die stacking, then electrical and mechanical bonding is achieved, but alignment precision requirements increase and non-wetting issues occur

Engineering Contradiction:

Improvebonding reliabilityVSAvoidpillar alignment precision

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The bonding interface is segmented into multiple functional zones: active copper pillars for electrical connection, and non-active pillars for mechanical support and alignment tolerance. This segmentation allows different regions to serve different purposes, reducing the precision burden on electrical bonding while maintaining overall reliability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The design changes the functional parameters of pillars by distinguishing between electrically active pillars (for signal/power transmission) and non-electrically active pillars (for mechanical support). This parameter differentiation allows the system to achieve bonding reliability without requiring all pillars to meet stringent electrical alignment specifications.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If non-electrically active pillars are added to prevent non-wetting, then bonding reliability improves, but device footprint increases

Engineering Contradiction:

Improvebonding reliabilityVSAvoidpackage footprint

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent merges the functions of mechanical support and electrical connection into a unified pillar structure. Non-electrically active pillars provide mechanical support and alignment tolerance without requiring separate support structures, thereby reducing the overall footprint while maintaining bonding reliability.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

Pillars are designed to serve multiple functions: electrically active pillars handle both mechanical support and electrical connection, while non-electrically active pillars provide mechanical support and alignment tolerance. This multi-functionality reduces the need for additional dedicated support structures, minimizing footprint expansion.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Adaptability or versatility

If pillar-to-pillar die stacking is used, then 3D integration is achieved, but large voids require underfill and dam structures

Engineering Contradiction:

Improve3D integration capabilityVSAvoidpackaging structure complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent extracts and eliminates the need for underfill and dam structures by redesigning the pillar configuration. The non-electrically active pillars are positioned to provide mechanical support and fill void spaces, making separate underfill and dam structures unnecessary. This extraction simplifies the overall packaging structure while maintaining 3D integration capability.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Non-electrically active pillars serve as intermediary elements that fill the void spaces between dice, providing mechanical support and eliminating the need for separate underfill materials. These intermediary pillars mediate the mechanical interface between stacked dice, reducing structural complexity.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 approach enhances the reliability of electrical and mechanical bonding, reduces the standoff distance between dice, and eliminates the need for underfill and dam structures, resulting in a more compact and reliable 3D device package.

Implementation Method 1

forming metal pillars or stud bumps using electroplating or wire bonding processes

Methodology Applied

Scientific EffectElectroplating: Electroplating

Data Source

PatentUS9508702B23D device packaging using through-substrate posts

Publication Date: 2016.11.29 NXP USA INC

AI summary

A method for 3D device packaging utilizes through-substrate metal posts to mechanically and electrically bond two or more dice. The first die includes a set of access holes extending from a surface of the first die to a set of pads at a metal layer of the first die. The second die includes a set of metal posts. The first die and the second die are stacked such that each metal post extends from a surface of the second die toward a corresponding pad via a corresponding access hole. The first die and second die are mechanically and electrically bonded via solder joints formed between the metal posts and the corresponding pads.