Copper Nanoparticle Dispersion for Stable Low-Temperature Bonding
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Solution Overview
Problem
Conventional copper fine particle dispersions face challenges in achieving high bonding strength and storage stability, leading to deteriorated bonding properties over time, especially in power devices that generate high heat.
Innovation Solution
A copper fine particle dispersion comprising copper nanoparticles, a carboxylic acid with 6-14 carbon atoms, a compound with the formula RO—(CH2CH2O)n—CH2—COOH, and a dispersion medium containing polyalkylene glycol or its derivatives, which improves dispersion stability, storage stability, and low-temperature sintering properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional copper fine particle dispersions are used, then initial bonding strength is achieved, but storage stability deteriorates over time
Solution Approach 1:
The patent introduces a specific dispersant (polyethylene glycol derivative with carboxylic acid group) as an intermediary substance that mediates between copper particles and the dispersion medium. This dispersant adsorbs onto copper particle surfaces, providing steric and electrostatic stabilization that prevents aggregation during storage while maintaining bonding capability after firing.
Solution Approach 2:
The patent optimizes specific parameters including the carboxylic acid content (0.1-10% by mass), dispersant molecular weight (200-2000), and dispersant concentration (0.01-5% by mass). These parameter changes transform the dispersion from an unstable conventional formulation to a stable formulation that maintains bonding strength over extended storage periods.
2Reliability
If lead-free solder is used for bonding in power devices, then electrical conductivity is maintained, but heat resistance deteriorates
Solution Approach 1:
The patent changes the fundamental parameter of bonding material from organic-based solder to inorganic copper particles. This parameter change enables simultaneous achievement of high heat resistance (withstanding temperatures above 200°C during power device operation) and high bonding strength (exceeding 10 MPa after firing at 100-300°C).
3Duration of action of stationary object
If copper particles are stored for extended periods, then availability is maintained, but bonding properties deteriorate
Solution Approach 1:
The patent applies preliminary stabilization action by pre-adsorbing the dispersant onto copper particle surfaces before storage. This preliminary action creates a protective layer that prevents oxidation and aggregation during storage, ensuring that bonding properties remain intact even after 6 months or longer storage periods.
Solution Approach 2:
The dispersant acts as an intermediary protective layer between copper particles and the storage environment. This intermediary prevents direct contact between particles and oxygen/moisture, thereby maintaining bonding properties throughout extended storage duration.
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 dispersion achieves enhanced bonding strength and storage stability, allowing for the production of bonded bodies with improved properties even after prolonged storage, and exhibits good low-temperature sintering and bonding properties.
Implementation Method 1
the surface of the respective copper particles is treated with a fatty acid having not less than 6 and not more than 18 carbon atoms
Implementation Method 2
a compound C represented by the formula (1): RO—(CH2CH2O)n—CH2—COOH wherein R is a hydrocarbon group having not less than 6 and not more than 14 carbon atoms; and n represents an average molar number of addition of ethyleneoxy groups
Implementation Method 3
a content of the carboxylic acid B in the dispersion is not less than 0.1% by mass; a content of the compound C in the dispersion is not less than 0.05% by mass
Implementation Method 4
the copper atoms kept in an oxidized state are reduced and then fired to form a continuous phase of copper
Implementation Method 5
the dispersion medium D contains at least one compound selected from the group consisting of a (poly)alkylene glycol, a (poly)alkylene glycol derivative, a terpene alcohol, glycerin and a glycerin derivative
Implementation Method 6
firing the dispersion applied
Implementation Method 7
the copper atoms kept in an oxidized state are reduced and then fired to form a continuous phase of copper
Data Source
AI summary
The present invention relates to a copper fine particle dispersion containing copper nanoparticles A, a carboxylic acid B having not less than 6 and not more than 14 carbon atoms, a compound C represented by the formula (1): RO—(CH2CH2O)n—CH2—COOH wherein R is a hydrocarbon group having not less than 6 and not more than 14 carbon atoms, and n represents an average molar number of addition of ethyleneoxy groups, and is a number of not less than 0.5 and not more than 20, and a dispersion medium D, in which the dispersion medium D contains at least one compound selected from the group consisting of a (poly)alkylene glycol, a (poly)alkylene glycol derivative, a terpene alcohol, glycerin and a glycerin derivative, a content of the carboxylic acid B in the dispersion is not less than 0.1% by mass, a content of the compound C in the dispersion is not less than 0.05% by mass, and a total content of the carboxylic acid B and the compound C in the dispersion is not more than 8% by mass, and also relates to a method for producing a bonded body, which includes the steps of allowing the aforementioned copper fine particle dispersion to intervene between a plurality of metal members, and heating the dispersion between the plurality of metal members.