Copper Powder for Low-Temperature Sintering
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Solution Overview
Problem
Conventional methods for producing copper powder result in particles that are either too large, leading to voids in conductive films and high electrical resistance, or too small, causing agglomeration and requiring protective layers that increase sintering temperatures, both of which are energetically disadvantageous.
Innovation Solution
A method involving the reduction of copper ions using hydrazine in a mixture of water and an organic solvent with water miscibility, which produces copper powder with an average primary particle size of 0.15 to 0.6 μm and no protective layer, allowing for low-temperature sintering and reduced voids in conductive films.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If copper particles of submicron size are used, then voids between particles are reduced in conductive films, but electrical resistance increases due to the large particle size
Solution Approach 1:
The patent applies parameter changes by precisely controlling the particle size of copper powder within the range of 0.15 to 0.6 μm and adjusting the D/DBET ratio to 0.8-4.0. This optimization of particle size parameters reduces voids in conductive films while maintaining low electrical resistance, resolving the contradiction between film density and electrical conductivity.
2Length of moving object
If copper nanoparticles are used, then particle size is reduced to nanometer order, but particles shrink considerably by heat of sintering and require protective layers
Solution Approach 1:
The patent changes the particle size parameter from nanometer scale to submicron scale (0.15-0.6 μm), which fundamentally alters the sintering behavior. This parameter change eliminates the need for protective layers and enables low-temperature sintering, as the particles are large enough to resist shrinkage but small enough to maintain high surface energy for easy sintering.
Solution Approach 2:
The patent extracts and eliminates the protective layer from the copper particle structure. By producing copper powder without protective layers through controlled reduction in a water-organic solvent mixture, the patent removes the barrier that would otherwise increase sintering temperature, enabling direct low-temperature sintering of pure copper particles.
3Stability of the object's composition
If protective layers are formed on copper nanoparticles, then agglomeration is prevented, but sintering temperature increases due to the protective agent
Solution Approach 1:
The patent extracts and eliminates the protective layer from the copper particle structure. By producing copper powder without protective layers through controlled reduction in a water-organic solvent mixture, the patent removes the barrier that would otherwise increase sintering temperature, enabling direct low-temperature sintering of pure copper particles.
Solution Approach 2:
The patent optimizes the particle size parameter to 0.15-0.6 μm with D/DBET ratio of 0.8-4.0, which provides natural dispersibility without requiring protective layers. This parameter optimization maintains particle stability while enabling low-temperature sintering.
4Ease of manufacture
If conventional reduction methods are used, then copper powder is produced, but particles are either too large causing voids or too small requiring protective layers
Solution Approach 1:
The patent applies parameter changes by controlling particle size within 0.15-0.6 μm and D/DBET ratio within 0.8-4.0 through specific reduction conditions. This precise parameter control produces copper powder with optimal properties for low-temperature sintering and dense film formation without requiring protective layers.
Solution Approach 2:
The patent uses a water-organic solvent mixture as an intermediary medium for the reduction reaction. This intermediary solvent system enables precise control of particle size and morphology during reduction, producing copper powder with the desired properties without requiring subsequent protective layer formation.
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 produces copper powder that is easily sinterable at low temperatures, forms dense conductive films with reduced specific resistance, and avoids the issues of agglomeration and high sintering temperatures associated with conventional techniques.
Implementation Method 1
a method involving the reduction of copper ions using hydrazine in a mixture of water and an organic solvent with water miscibility, which produces copper powder
Implementation Method 2
an organic solvent having water miscibility and capable of reducing the surface tension of water
Data Source
AI summary
Disclosed is copper powder having an average primary particle size D of 0.15 to 0.6 μm, having a ratio of D to DBET, D/DBET, of 0.8 to 4.0 wherein DBET is a sphere-equivalent average particle diameter calculated from a BET specific surface area, and having no layer for preventing agglomeration on the surface thereof. The copper powder is suitably produced by a method which includes a step of mixing (1) hydrazine and (2) a reactant mixture including a monovalent or divalent copper source and a liquid medium which includes water and an organic solvent having water miscibility and capable of reducing the surface tension of water, to reduce the copper source to form copper particles.