Conductive Silver Paste for Nitrogen-Sintered Copper Bonding
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Solution Overview
Problem
Conventional electrically conductive pastes do not provide sufficient bonding strength when bonding a Cu substrate or Cu electrode without a plating layer to electronic components, especially when sintered in a nitrogen atmosphere.
Innovation Solution
The use of a specific combination of silver powders with different particle size ranges and median diameters, including flake-like silver powder A, silver powder B, and silver powder C, optimized in terms of content and particle size distribution, to enhance bonding strength between the Cu substrate or Cu electrode and electronic components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If electrically conductive paste is applied directly to Cu substrate or Cu electrode without plating layer and sintered in air atmosphere, then manufacturing process is simplified and cost is reduced, but copper oxide layer forms on surface preventing sufficient bonding
Solution Approach 1:
The patent applies inert atmosphere (nitrogen or vacuum) during sintering to prevent copper oxidation on the substrate surface. This allows direct application of conductive paste to unplated Cu substrates while maintaining bonding strength, as the inert environment prevents harmful oxide formation that would otherwise occur in air atmosphere.
Solution Approach 2:
The patent changes the atmospheric parameters (oxygen concentration) during sintering to control the chemical state of the copper surface. By reducing oxygen partial pressure through nitrogen atmosphere or vacuum, the copper surface remains in metallic state rather than oxidizing, enabling strong bonding without plating layers.
2Object-affected harmful factors
If electrically conductive paste is applied directly to Cu substrate without plating layer and sintered in nitrogen atmosphere, then copper oxidation is prevented, but bonding strength between Cu substrate and sintered body becomes insufficient
Solution Approach 1:
The patent uses a composite metal powder composition containing multiple components (silver, copper, and other metals) in specific ratios. This composite structure provides both oxidation resistance during sintering in nitrogen atmosphere and strong bonding capability to the copper substrate, overcoming the limitations of single-material pastes.
Solution Approach 2:
The patent optimizes physical parameters of the conductive paste including particle size distribution, metal composition ratios, and binder content. These parameter changes enhance the paste's ability to bond to copper substrates in nitrogen atmosphere while preventing oxidation, achieving both protection and strong adhesion.
3Ease of manufacture
If conventional electrically conductive paste is used for bonding Cu substrate without plating layer, then manufacturing cost is reduced, but bonding strength to electronic components becomes insufficient
Solution Approach 1:
The patent employs a composite metal powder system with silver, copper, and additional metal elements in optimized proportions. This composite composition provides enhanced bonding strength to electronic components while maintaining the cost advantages of using unplated copper substrates, unlike conventional single-metal pastes.
Solution Approach 2:
The patent creates local quality variations in the conductive paste through specific metal composition and particle size distribution. The paste contains components with different properties that locally enhance bonding to both the copper substrate and electronic components, providing strong adhesion at both interfaces while maintaining overall cost efficiency.
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 optimized silver powder combination ensures excellent bonding strength and conductivity, even when sintered in a nitrogen atmosphere, without the need for a plating layer, by filling gaps and forming continuous contacts between silver powders.
Implementation Method 1
the electrically conductive paste is sintered in nitrogen atmosphere instead of air atmosphere
Data Source
Figure 1~2
Figure 3A~3B
Figure 4~5
AI summary
An object of the present invention is to provide an electrically conductive paste having excellent bonding strength when bonded to an electronic substrate and the like, a laminated body, and a method for bonding a Cu substrate or Cu electrode to an electrical conductor. An electrically conductive paste comprising: a flake-like silver powder A having a particle size in the range of 1 µm or more and 15 µm or less and having a median diameter D50 of 2 µm or more and 5 µm or less; a silver powder B having a particle size in the range of 25 µm or more and 100 µm or less and having a median diameter D50 of 30 µm or more and 40 µm or less; a silver powder C having a particle size in the range of 10 nm or more and 190 nm or less and having a median diameter D50 of 50 nm or more and 150 nm or less; and a solvent, wherein the content of the silver powder C is more than 5.0 parts by mass and less than 90.0 parts by mass based on 100 parts by mass in total of the flake-like silver powder A, the silver powder B, and the silver powder C.