Fine Copper Particles with Cuprous Oxide Coating for Low-Temperature Sintering
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Solution Overview
Problem
Fine copper particles coated with antioxidants to prevent oxidation require high sintering temperatures, making them unsuitable for resin substrates with low heat resistance, leading to increased costs and limited use in electronic devices and printed wiring boards.
Innovation Solution
Fine copper particles with a surface coating film of cuprous oxide, having an average film thickness of 1.5 nm or less, are produced using a reducing flame with a specific CO/CO2 volume ratio, allowing for lower sintering temperatures and improved sinterability without the need for additional antioxidants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the surface of fine copper particles is coated with an antioxidant to prevent oxidation, then the oxidation resistance is improved, but the sintering temperature must be increased to remove the coating
Solution Approach 1:
The invention changes the chemical composition parameter of the coating from antioxidant to cuprous oxide, and controls the thickness parameter to 1.5 nm or less. This allows the coating to provide sufficient oxidation protection while being easily reducible at low temperatures during sintering, resolving the contradiction between oxidation resistance and sintering temperature requirements
Solution Approach 2:
The invention creates a composite structure with a copper core and cuprous oxide coating layer. This composite material combines the oxidation resistance of the oxide coating with the electrical conductivity of the copper core, while the thin coating thickness enables low-temperature sintering
2Reliability
If the sintering temperature is increased to remove thick antioxidant coatings, then the coating can be reliably removed, but resin substrates with low heat resistance cannot be used
Solution Approach 1:
By changing the coating material to cuprous oxide and controlling thickness to 1.5 nm or less, the coating becomes easily reducible at low temperatures. This enables complete coating removal at low sintering temperatures, allowing the use of heat-sensitive resin substrates and expanding substrate material options
3Reliability
If a thick coating is applied to prevent oxidation, then oxidation protection is improved, but sintering temperature must be increased
Solution Approach 1:
The invention optimizes the thickness parameter to 1.5 nm or less and changes the chemical composition to cuprous oxide. This thin oxide coating provides adequate oxidation protection for fine copper particles while requiring minimal energy for reduction during sintering, maintaining low sintering temperature
Solution Approach 2:
The invention applies a minimal thickness of cuprous oxide coating (1.5 nm or less) which is sufficient to prevent oxidation during storage and handling, but thin enough to be easily removed at low sintering temperatures, achieving partial coverage that balances protection and processability
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 effectively suppresses oxidation and reduces sintering temperatures, enabling the use of fine copper particles in high-density wiring on low-heat resistance resin substrates, thereby lowering the cost of electronic devices and printed wiring boards while maintaining excellent sinterability.
Implementation Method 1
heating copper or a copper compound in a reducing flame formed by a burner wherein the fine copper particles are produced by adjusting a mixing ratio between a combustible gas and a combustion supporting gas which form the reducing flame
Data Source
AI summary
A method for producing fine copper particles includes producing fine copper particles having a coating film containing cuprous oxide on a surface by heating copper or a copper compound in a reducing flame formed by a burner. The fine copper particles are produced by adjusting a mixing ratio between a combustible gas and a combustion supporting gas which form the reducing flame such that a volume ratio of CO/CO2 is in a range of 1.5 to 2.4.