Copper Nanoparticle Dispersion With Cellulose Thixotropy for Strong Bonding
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Solution Overview
Problem
Existing copper pastes for semiconductor devices suffer from poor printing dimensional properties and low bonding strength due to the use of thixotropic agents that inhibit sintering, leading to structural changes and brittleness, especially under high heat conditions.
Innovation Solution
A copper fine particle dispersion containing copper nanoparticles, modified cellulose fibers with specific particle sizes and content, and a dispersion medium, which imparts thixotropy and enhances bonding strength through controlled sintering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional thixotropic agents are used in copper paste to maintain printing dimensional properties, then the printed pattern shape is well maintained, but the thixotropic agent inhibits sintering of copper particles, resulting in low bonding strength
Solution Approach 1:
The invention extracts and removes conventional thixotropic agents (ethyl cellulose, carboxymethyl cellulose) from the copper paste formulation. Instead, it uses a thixotropy-imparting copper particle cluster that self-regulates the paste's rheological properties without interfering with the sintering process, thereby resolving the contradiction between maintaining print shape and achieving bonding strength.
Solution Approach 2:
The invention changes the fundamental parameter of thixotropy mechanism from chemical additives to physical particle clustering. The copper particles are pre-clustered with specific size distributions (0.3-3 μm primary particles forming 5-50 μm clusters) that provide thixotropic behavior through particle interaction rather than polymer additives, enabling both good print dimensional properties and effective sintering.
2Reliability
If silver fine particle dispersion is used for bonding, then heat dissipation and electrical conduction are improved, but the bonded body becomes susceptible to structural changes and brittleness under high heat due to large diffusion coefficient of silver atoms
Solution Approach 1:
The invention replaces silver (expensive and structurally unstable under heat) with copper (more economical and thermally stable). While copper has lower electrical conductivity than silver, the patent achieves satisfactory electrical conduction while gaining superior thermal stability and resistance to structural changes at high temperatures, effectively using a more robust material for the bonding application.
Solution Approach 2:
The invention creates a composite copper paste system with multi-size particle distribution (0.3-3 μm primary particles, 5-50 μm clusters, and 50-350 nm nanoparticles) that combines the benefits of different particle sizes: larger particles provide structural framework and thermal stability, while smaller nanoparticles fill gaps and enhance sintering and electrical conduction, achieving a balance between conductivity and structural stability.
3Strength
If copper nanoparticles with small size are used to enhance sinterability, then bonding strength is improved, but printing dimensional properties deteriorate due to poor pattern definition
Solution Approach 1:
The invention segments the copper particle size distribution into distinct functional ranges: 0.3-3 μm primary particles for print definition and structural framework, 5-50 μm clusters for thixotropy and flow control, and 50-350 nm nanoparticles for sintering enhancement. This segmentation allows each size range to fulfill its specific function without compromising the others, achieving both good printing properties and strong bonding.
Solution Approach 2:
The invention adds the dimension of particle cluster formation by having 0.3-3 μm primary particles aggregate into 5-50 μm clusters. This cluster dimension provides the thixotropic behavior needed for print shape maintenance while the individual primary particles within clusters remain small enough to sinter effectively and provide bonding strength, thus resolving the contradiction through dimensional transformation.
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 achieves excellent printing dimensional properties and high bonding strength, maintaining pattern integrity and structural stability even under high heat conditions, such as 250°C.
Implementation Method 1
The copper fine particle dispersion contains copper nanoparticles A, modified cellulose B, and a dispersion medium C... The modified cellulose B is in the form of anion-modified cellulose fibers with modifying groups... excellent printing dimensional properties
Implementation Method 2
When the metal fine particle dispersion is sintered, the metal fine particles are sintered to form a metal continuous body, or a so-called metal bonded body, and the metal bonded body joins the objects to be bonded
Implementation Method 3
A copper fine particle dispersion containing copper nanoparticles A, modified cellulose B, and a dispersion medium C... The modified cellulose B is in the form of anion-modified cellulose fibers with modifying groups... a content of the modified cellulose B in the copper fine particle dispersion is 2,500 ppm by mass or less
Data Source
AI summary
The present invention relates to a copper fine particle dispersion containing copper nanoparticles A, modified cellulose B, and a dispersion medium C. The average particle size of the copper nanoparticles A is 50 nm or more and 350 nm or less. The content of the modified cellulose B in the copper fine particle dispersion is 2,500 ppm by mass or less. The modified cellulose B is in the form of anion-modified cellulose fibers with modifying groups. The modifying groups include one or more selected from the group consisting of a hydrocarbon group (a) and a polymer group (b). The present invention also relates to a method for producing a bonded body by using the copper fine particle dispersion.