Fine Silver Particle Dispersion for Low-Temperature Sintering
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Solution Overview
Problem
Existing fine silver particle dispersions face challenges in achieving good storage stability of resistivity and forming electrically conductive thick films with low resistivity and smooth surfaces, particularly due to high resistivity and poor sintering at low temperatures.
Innovation Solution
A fine silver particle dispersion comprising 65-95.4% fine silver particles with an average primary particle diameter of 10-190 nm, 4.5-34.5% solvent, and 0.1-1.0% ethyl cellulose with a weight average molecular weight of 10,000-120,000, which enhances dispersion stability and allows for low-temperature sintering, resulting in films with low resistivity and smooth surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fine silver particle dispersions are used, then the dispersion can be applied to form conductive films, but the storage stability of resistivity is poor and the sintering temperature must be high
Solution Approach 1:
The patent changes the molecular weight parameter of the cellulose derivative dispersant to a specific range (10,000-120,000), which fundamentally alters the dispersion stability and sintering behavior. This parameter optimization enables low-temperature sintering while maintaining excellent storage stability of resistivity, resolving the contradiction between reliability and temperature requirements.
Solution Approach 2:
The patent uses a composite system combining fine silver particles with a specifically selected cellulose derivative dispersant. This composite approach creates a synergistic effect where the dispersant protects the silver particles during storage (improving resistivity stability) and facilitates low-temperature sintering, thus resolving the contradiction between storage stability and sintering temperature.
2Quantity of substance
If high silver particle concentration is used, then conductive films can be formed, but the surface smoothness deteriorates
Solution Approach 1:
The patent optimizes the molecular weight parameter of the dispersant to achieve optimal steric stabilization. This parameter change allows high silver particle concentration to be maintained while the dispersant prevents aggregation and ensures uniform distribution, thereby maintaining surface smoothness even at high concentrations.
Solution Approach 2:
The cellulose derivative acts as an intermediary between silver particles, providing steric stabilization that prevents aggregation. This intermediary mechanism allows high particle concentration to be achieved without compromising surface smoothness, as the dispersant maintains uniform particle distribution throughout the dispersion.
3Volume of stationary object
If low molecular weight dispersants are used, then viscosity is reduced, but dispersion stability and sintering performance worsen
Solution Approach 1:
The patent identifies and optimizes the molecular weight parameter of the dispersant to a specific range (10,000-120,000). This parameter optimization achieves the optimal balance between viscosity and stability: the dispersant is not too small to fail providing steric stabilization, yet not too large to cause excessive viscosity, thereby simultaneously improving dispersion stability and maintaining manageable viscosity.
Solution Approach 2:
The patent uses a moderate amount of dispersant with optimized molecular weight, avoiding both insufficient dispersant (which would cause aggregation) and excessive dispersant (which would increase viscosity). This partial action approach achieves the optimal balance between dispersion stability and viscosity control.
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 provides stable resistivity and enables the formation of electrically conductive thick films with low resistivity and good surface smoothness, suitable for various electronic devices, including solar cells and LEDs, through effective sintering at reduced temperatures.
Implementation Method 1
fine silver particle dispersion comprising: (1) 65 to 95.4% by weight of fine silver particles... (3) 0.1 to 1.0% by weight of ethyl cellulose
Implementation Method 2
allows for low-temperature sintering, resulting in films with low resistivity and smooth surfaces
Data Source
AI summary
This disclosure relates to a conductive paste comprising a fine silver particle dispersion and a glass frit, wherein the fine silver particle dispersion comprising: (1) 65 to 95.4% by weight of fine silver particles which have average primary particle diameter of 10 to 190 nm and which comprise 25% by number or less of silver particles having primary particle diameter of 100 nm or larger, (2) 4.5 to 34.5% by weight of a solvent, (3) 0.1 to 1.0% by weight of ethyl cellulose having weight average molecular weight of 10,000 to 120,000. Also provided are: a method of manufacturing an electrically conductive thick film comprising steps of: (a) applying said fine silver particle dispersion on a substrate, and (b) heating the applied fine silver particle dispersion at 80 to 1000° C.; and an electrical device comprising a conductive thick film made with the foregoing paste.