Copper-Copper Bonding Using Hydrazine Pretreatment to Minimize Voids

Solution Overview

Problem

Existing bonding methods for copper-copper metal in three-dimensional packaging often result in poor bonding strength due to the presence of intermediate layers, which increase voids between bonding surfaces.

Innovation Solution

A bonding method involving pretreatment of a copper-plated surface with hydrazine hydrate under a protective atmosphere, followed by pressurized bonding at elevated temperatures, eliminating the need for intermediate layers and enhancing bonding strength.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If welding or adhesive bonding is used for copper-copper metal bonding, then connection strength is improved, but voids between bonding surfaces increase due to intermediate layers

Engineering Contradiction:

Improvebonding strengthVSAvoidbonding quality

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The patent removes the intermediate layer (solder or adhesive) entirely from the bonding interface, achieving direct copper-to-copper contact. This extraction of the problematic intermediate layer eliminates the source of void formation while maintaining strong bonding through direct metallurgical bonding and atomic diffusion between copper surfaces.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces a protective atmosphere (inert gas or vacuum) as a mediator during the bonding process. This protective atmosphere prevents oxidation of copper surfaces during heating and bonding, enabling direct copper-copper contact without requiring traditional intermediate bonding layers, thus achieving both strength and reliability.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of manufacture

If intermediate layers (solder or adhesive) are used for bonding, then connection is achieved, but voids between bonding surfaces increase

Engineering Contradiction:

Improvebonding processabilityVSAvoidbonding quality

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent removes the intermediate layer (solder or adhesive) entirely from the bonding interface, achieving direct copper-to-copper contact. This extraction of the problematic intermediate layer eliminates the source of void formation while maintaining strong bonding through direct metallurgical bonding and atomic diffusion between copper surfaces.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent changes the bonding parameters by using elevated temperatures (200-300°C) and applying pressure in a protective atmosphere. These parameter changes enable direct copper-copper bonding without intermediates, achieving both manufacturability and high bonding quality with minimal voids.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If direct copper-copper contact is achieved without intermediate layers, then voids between bonding surfaces decrease, but bonding process complexity increases

Engineering Contradiction:

Improvebonding qualityVSAvoidbonding process complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent changes the bonding parameters by using elevated temperatures (200-300°C) and applying pressure in a protective atmosphere. These parameter changes enable direct copper-copper bonding without intermediates, achieving both manufacturability and high bonding quality with minimal voids.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses a protective atmosphere (inert gas or vacuum) to prevent oxidation during the bonding process. This creates a controlled environment that enables direct copper-copper contact without requiring complex intermediate bonding layers, simplifying the overall process while maintaining high bonding quality.

Inventive Principle:

Principle #39Inert atmosphere (Inert environment)

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

The method achieves a high bonding strength of up to 22 MPa with minimal voids between copper-plated contact surfaces, improving the reliability of three-dimensional packaging.

Implementation Method 1

the hydrazine hydrate reacts with an oxide layer on a surface of the copper-plated substrate to remove most of surface oxides

Methodology Applied

Scientific EffectChemical reduction: Reduction

Implementation Method 2

the mutual diffusion of copper atoms on the pretreated surface leads to the bonding of two copper-plated substrates

Methodology Applied

Scientific EffectDiffusion: Diffusion

Implementation Method 3

subjecting a copper-plated surface of a clean copper-plated substrate to pretreatment with hydrazine hydrate under a protective atmosphere

Methodology Applied

Scientific EffectOxidation prevention: Oxidation

Data Source

PatentUS12322724B2Bonding method for copper-copper metal with hydrazine hydrate

Publication Date: 2025.06.03 ANHUI UNIV

AI summary

The present disclosure belongs to the technical field of three-dimensional packaging, and in particular relates to a bonding method for a copper-copper metal. The bonding method includes: subjecting a copper-plated surface of a clean copper-plated substrate to pretreatment with hydrazine hydrate under a protective atmosphere, to obtain a copper-plated substrate to be bonded, where the copper-plated surface is kept at 50° C. to 90° C.; and subjecting a plurality of the copper-plated substrates to be bonded to pressurized bonding at 200°° C. to 300°° C. under the protective atmosphere.