Conductive Paste Copper Particle Aspect Ratio
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Solution Overview
Problem
Conventional electrically conductive copper pastes face issues with clogging during screen printing, poor sintering properties, and increased wiring resistance due to particle shape and oxidation, especially when baked in oxygen-containing atmospheres.
Innovation Solution
An electrically conductive paste with copper-based metal particles having a mean aspect ratio of 1.0 to 2.2, 90% particle diameter of 0.3 to 7.0 µm, and 50% particle diameter of 0.1 to 3.4 µm, with controlled oxygen concentration and minimal impurities, is used, along with a specific baking process in an inert gas or vacuum atmosphere to prevent oxidation and optimize sintering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional copper particles with flat flake-like or sharp needle-like shapes are used, then the paste can be manufactured easily, but clogging occurs during screen printing leading to decreased metal particle density and wiring pattern spreading
Solution Approach 1:
The patent changes the shape parameter of copper particles from flat flake-like or sharp needle-like shapes to spherical shapes with controlled aspect ratios (0.5-2.0). This parameter change eliminates clogging during screen printing while maintaining ease of manufacture, thereby improving wiring pattern precision without sacrificing manufacturing efficiency.
2Quantity of substance
If copper particles are used to reduce cost compared to silver, then material cost decreases, but oxidation resistance deteriorates leading to increased wiring resistance
Solution Approach 1:
The patent introduces glass particles as an intermediary protective layer around copper particles. This glass coating acts as a barrier against oxidation, allowing the use of cost-effective copper particles while preventing oxidation-related deterioration. The glass particles mediate between the low-cost copper material and the requirement for oxidation resistance, achieving both cost reduction and reliability improvement.
3Reliability
If binder resin content is reduced to improve sintering properties, then wiring resistance decreases, but printing performance deteriorates due to insufficient binding
Solution Approach 1:
The patent changes the particle shape parameter to spherical copper particles with aspect ratios of 0.5-2.0, which improves packing density and sintering behavior. This shape parameter change enhances sintering properties without requiring increased binder resin content, thereby maintaining printing performance while improving sintering quality and reducing wiring resistance.
4Loss of substance
If copper particles are baked in oxygen-containing atmosphere to remove binder resin, then residual resin decreases, but copper oxidation increases leading to poor sintering property
Solution Approach 1:
The patent employs an inert atmosphere (nitrogen or vacuum) during the baking process to prevent copper oxidation. This inert environment allows for effective binder resin removal through controlled heating while protecting copper particles from oxidation. The inert atmosphere resolves the contradiction by enabling resin decomposition without compromising sintering properties, achieving both low residual resin and high reliability.
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
This approach prevents clogging and width-spreading during printing, improves sintering properties, and reduces wiring resistance, achieving low resistance and reliable wiring patterns in electronic components and silicon solar cells.
Implementation Method 1
a specific baking process in an inert gas or vacuum atmosphere to prevent oxidation and optimize sintering
Implementation Method 2
baking process in an inert gas or vacuum atmosphere to prevent oxidation
Data Source
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AI summary
This conductive paste is such that the printing properties and sintering properties are superior and is formed such that resistance of wiring after sintering is lowered. This conductive paste is characterized by being formed from copper-based metal particles and by an aspect ratio (dmax/dmin), which is defined as the ratio of the maximum diameter (dmax) and minimum diameter (dmin) for the metal particles, being greater than or equal to 1.0 and smaller than 2.2.