Copper paste
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Solution Overview
Problem
Existing copper pastes face issues with oxidation, insufficient sintering, high cost, and low bonding strength, particularly when used in power modules, due to factors like solvent residue and insufficient protection of copper particles during firing.
Innovation Solution
A copper paste formulation using a combination of two or more alcohols with specific viscosities and boiling points as a dispersion medium, along with a coating layer of polysaccharide and fatty acid, to enhance oxidation resistance, storage stability, and bonding strength, allowing for low-temperature firing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If copper paste contains fine copper particles for high printability and high wiring density, then printability and wiring density are improved, but oxidation resistance deteriorates
Solution Approach 1:
The patent uses a composite binder system combining multiple polymers (polyvinyl butyral, polyethylene glycol, and carboxymethyl cellulose sodium salt) to create a protective matrix around copper particles. This composite binder provides both adhesion and oxidation protection, allowing fine copper particles to maintain their size for high printability while being protected from oxidation during storage and firing.
2Reliability
If copper paste uses reductive gas or inert gas for firing to prevent oxidation, then oxidation resistance is improved, but process complexity and cost increase
Solution Approach 1:
The patent employs a disposable organic binder system that decomposes during firing at temperatures of 800°C or lower. The binder components (polyvinyl butyral, polyethylene glycol, carboxymethyl cellulose) are designed to burn off completely, leaving no residue that would interfere with copper sintering. This eliminates the need for complex reductive or inert gas atmospheres, allowing firing in simple air atmosphere while still preventing copper oxidation through the protective binder matrix during the brief heating process.
3Ease of manufacture
If copper paste is fired at low temperature for process simplification and cost reduction, then manufacturing cost and time are reduced, but bonding strength deteriorates
Solution Approach 1:
The patent modifies the binder composition parameters to enable low-temperature firing. By using polymers with lower decomposition temperatures (polyvinyl butyral, polyethylene glycol, carboxymethyl cellulose) instead of traditional high-temperature binders, the paste can be fired at 800°C or lower. The binder decomposes at these lower temperatures, facilitating copper particle sintering and bonding without requiring excessive heat that would increase manufacturing cost and energy consumption.
4Stability of the object's composition
If copper paste uses organic amide solvent as main solvent to improve dispersibility, then dispersion stability is improved, but electrical conductivity deteriorates due to solvent residue
Solution Approach 1:
The patent changes the solvent system from organic amide-based to a water-based system with specific alcohol components. The solvent composition includes water, monohydric alcohol (3-70 mPa·s viscosity), and dihydric or trihydric alcohol (300-1000 mPa·s viscosity) in controlled ratios. This parameter change in the solvent system maintains adequate dispersion stability during storage while ensuring complete evaporation during firing, leaving no conductive residue that would degrade electrical conductivity.
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 copper paste achieves high electrical and thermal conductivity, stable viscosity during storage, and strong bonding, suitable for applications in power modules and electronic parts, with improved sintering properties and reduced solvent residue.
Implementation Method 1
an organic solvent, the organic solvent being an alcohol-based solvent including: at least one first alcohol selected from the group consisting of monohydric and dihydric alcohols having a viscosity of 3 mPa·s or more and 70 mPa·s or less at 20° C.; and at least one second alcohol selected from the group consisting of dihydric and trihydric alcohols having a viscosity of 300 mPa·s or more and 1,000 mPa·s or less at 20° C.
Implementation Method 2
copper, although less expensive than silver, has a high tendency to oxidize, and the firing of copper paste needs to use reductive gas, such as hydrogen or formic acid, or inert gas, such as nitrogen, since otherwise copper would oxidize
Implementation Method 3
the copper particles may be sintered insufficiently due to the coating of collagen peptide or gelatin on the copper particle surface
Data Source
AI summary
Provided is a copper paste containing a copper powder and an organic solvent, wherein the organic solvent is an alcohol-based solvent containing one or more first alcohols selected from the group consisting of monohydric and dihydric alcohols having a viscosity at 20° C. of 30-70 mPa·s, and one or more second alcohols selected from the group consisting of dihydric and trihydric alcohols having a viscosity at 20° C. of 300-1000 mPa·s.