Silver Powder Particle Distribution for Low-Resistivity Conductive Films
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Solution Overview
Problem
Conventional silver powders produced by wet reduction methods face challenges in achieving a balance between small particle diameter, high tap density, and controlled specific surface area, leading to poor film coating and increased volume resistivity, which hinders the formation of dense and fine conductor patterns.
Innovation Solution
A production method involving high-pressure airflow milling and classification of silver powder, with controlled concentrations, achieves a tap density of 4.8 g/mL, a TAP/D50 value of 7-15, and a specific surface area of 0.75-1.3 m2/g, resulting in improved packability and dispersibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the particle diameter of silver particles is reduced in production by wet reduction method, then the specific surface area increases, but the tap density decreases
Solution Approach 1:
The patent applies parameter changes by controlling the concentration of silver powder during the milling step (0.05 to 0.5 kg/m³) and adjusting the classification parameters to achieve a specific particle size distribution. This results in silver powder with optimized parameters: tap density of 4.0-6.0 g/mL and specific surface area of 0.5-2.0 m²/g, resolving the contradiction between increased surface area and maintained density
2Manufacturing precision
If the particle diameter of silver particles is reduced, then the line properties improve, but the volume resistivity increases
Solution Approach 1:
The patent applies local quality by creating a bimodal particle size distribution where fine particles (small diameter) provide good line properties and fillability, while coarser particles maintain low volume resistivity. The classification step separates particles into different size ranges, with each size range contributing different local qualities to the final conductive paste performance
Solution Approach 2:
The patent creates a composite particle size distribution system combining fine and coarse silver particles in specific proportions. This composite structure allows the fine particles to improve line properties while the coarse particles maintain electrical conductivity, achieving both good line properties and low volume resistivity simultaneously
3Ease of operation
If the specific surface area of silver powder is increased, then the dispersibility improves, but the packability decreases
Solution Approach 1:
The patent optimizes the concentration parameter during milling (0.05 to 0.5 kg/m³) to control particle surface characteristics and morphology. This parameter control achieves a balance where particles have sufficient surface area for good dispersibility (0.5-2.0 m²/g) while maintaining appropriate particle density and shape for good packability (4.0-6.0 g/mL tap density)
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 silver powder with reduced volume resistivity, enabling better filling of voids and enhancing electrical conductivity in conductive films.
Implementation Method 1
a milling step of using high-pressure airflow to accelerate and mill a silver powder produced by a wet reduction method
Implementation Method 2
a classification step of classifying the silver powder, performed after the milling step
Data Source
AI summary
Provided are a silver powder having powder physical properties enabling reduction of volume resistivity after firing and a method of producing this silver powder. The silver powder has a tap density of 4.8 g/mL or more, a TAP/D50 value (value determined by dividing the tap density (g/mL) by the volume-based median diameter (μm)) of not less than 7 and not more than 15, and a specific surface area of not less than 0.75 m2/g and not more than 1.3 m2/g.