Copper Fine Particles Low-Temperature Sintering Coating

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Solution Overview

Problem

Copper fine particles sintered at high temperatures pose challenges due to carbon adherence and increased oxygen concentration, leading to inhibited sintering and reduced productivity, especially when used in conductive inks or pastes on resin substrates with low heat resistance, resulting in cost and productivity issues.

Innovation Solution

Copper fine particles with a coating film containing cuprous oxide and copper carbonate, where the copper carbonate amount is controlled between 0% to 20% by mass, and the carbon to specific surface area ratio is maintained between 0.008% to 0.020% by mass·g/m2, allowing for sintering at lower temperatures (120° C to 150° C) by adjusting the carbon amount in the fuel gas and using an inert gas atmosphere for cooling and post-processing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If copper fine particles are sintered at high temperatures, then conductivity is improved, but resin substrates with low heat resistance cannot be used and cost increases

Engineering Contradiction:

ImproveconductivityVSAvoidresin substrate compatibility

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The invention changes the sintering temperature parameter from conventional high temperatures (requiring polyimide substrates) to low temperatures (100-200°C) enabling use of PET and other low heat-resistance substrates. This is achieved through surface modification of copper particles with specific coatings that facilitate low-temperature sintering while maintaining conductivity.

Inventive Principle:

Principle #35Parameter changes

2Temperature

If particle diameter is reduced to lower sintering temperature, then sintering temperature decreases, but oxygen concentration increases and dispersibility worsens

Engineering Contradiction:

Improvesintering temperatureVSAvoidoxygen concentration

Core Design Contradiction:

TemperatureVSStability of the object's composition

Solution Approach 1:

The invention introduces a coating layer as an intermediary substance on the copper particle surface. This coating acts as a barrier that prevents oxygen from penetrating into the particle core, thereby controlling oxygen concentration even when particles are reduced to small diameters (60-100 nm). The coating enables low-temperature sintering while maintaining compositional stability.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention creates composite structures by combining copper core material with surface coating materials. This composite approach allows the interior copper to maintain low oxygen content while the surface coating facilitates low-temperature sintering and prevents oxygen diffusion, resolving the contradiction between particle size reduction and oxygen control.

Inventive Principle:

Principle #40Composite materials

3Reliability

If carbon is generated in the producing process, then reduction is enhanced, but carbon adheres to particle surface and inhibits sintering

Engineering Contradiction:

Improvereduction efficiencyVSAvoidcarbon adhesion

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The invention converts the harmful effect of carbon adhesion into a beneficial surface coating. By controlling the producing process to generate carbon that forms a uniform coating layer on particle surfaces rather than adhering as impurity, the carbon layer becomes beneficial by facilitating low-temperature sintering while the underlying copper remains properly reduced.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 approach enables copper fine particles to be sintered at lower temperatures without increasing costs or decreasing productivity, facilitating their use in high-density wiring on low-heat resistance resin substrates, thereby reducing costs in electronic devices and printed wiring boards.

Implementation Method 1

metal or a metal compound as a raw material is blown into the reducing flame to heat, reduce, and evaporate

Methodology Applied

Scientific EffectEvaporation: Evaporation

Implementation Method 2

metal or a metal compound as a raw material is blown into the reducing flame to heat, reduce, and evaporate

Methodology Applied

Scientific EffectReduction: Reduction

Data Source

PatentUS11253921B2Copper fine particle, method for producing same, and sintered body

Publication Date: 2022.02.22 NIPPON SANSO CORP

AI summary

An object of the present invention to provide copper fine particles which can be sintered at a lower temperature than that of the conventional copper fine particles without causing a cost increase, a decrease in productivity, a method for producing the copper fine particles, and a sintered body, and the present invention provides copper fine particles having a coating film containing cuprous oxide and copper carbonate on the surface thereof.