Bimodal Conductive Paste for Low-Temperature Sintering
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Solution Overview
Problem
Conductive pastes containing copper fillers face challenges such as oxidation, high sintering temperatures, and substrate damage due to the limitations of existing capping agents and particle size distributions, which affect the conductivity and reliability of printed films.
Innovation Solution
A method for preparing conductive pastes with bimodal particle size distribution using a mixture of micron-sized or finer metal flakes and metal nanoparticles, allowing for lower temperature sintering and improved anti-oxidation properties, achieved through a three-step process involving the synthesis of nanoparticles and flakes with controlled size and morphology, and the use of a polymer matrix to form a stable paste.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper particles are passivated by a coating to prevent oxidation, then anti-oxidation properties are improved, but sintering temperature increases and substrate damage occurs
Solution Approach 1:
The copper filler is segmented into two distinct size groups: micron-sized particles (5-1000 μm) that provide structural framework and larger surface area for conduction, and nanoparticles (5-1000 nm) that enable lower temperature sintering due to melting point depression. This segmentation allows each size to fulfill different functional requirements, resolving the contradiction between oxidation resistance and sintering temperature.
Solution Approach 2:
The invention creates a composite filler system combining copper flakes and copper nanoparticles in specific weight ratios (20-80 wt% flakes, 80-20 wt% nanoparticles). This composite structure leverages the advantages of both particle types: the flakes provide conductivity network and oxidation resistance, while the nanoparticles enable low-temperature processing. The synergistic combination resolves the technical contradiction between maintaining reliability and reducing processing temperature.
2Temperature
If copper nanoparticles are used to enable lower temperature sintering, then substrate damage is reduced, but the printed film has a high tendency to crack
Solution Approach 1:
The filler is segmented into two size categories where micron-sized particles (5-1000 μm) form a robust structural framework that prevents cracking, while nanoparticles (5-1000 nm) enable low-temperature sintering. The larger particles act as structural anchors that maintain film integrity during and after the low-temperature sintering process, resolving the contradiction between temperature reduction and strength maintenance.
Solution Approach 2:
The composite filler system combines copper flakes (20-80 wt%) that provide mechanical strength and crack resistance with copper nanoparticles (80-20 wt%) that enable low-temperature sintering. The flake particles form an interconnected network that maintains film integrity, while the nanoparticles facilitate sintering at temperatures below 100°C. This composite approach simultaneously achieves both low-temperature processing and high film strength.
3Reliability
If copper flakes are used to provide more contacting points for conduction, then conductivity is improved, but sintering temperature increases
Solution Approach 1:
The copper filler is segmented into two size groups: micron-sized particles (5-1000 μm) that provide extensive surface area and numerous contacting points for electrical conduction, and nanoparticles (5-1000 nm) that enable low-temperature sintering through melting point depression. This segmentation allows the micron particles to fulfill the conductivity requirement while the nanoparticle component enables low-temperature processing, resolving the contradiction between conductivity and sintering temperature.
Solution Approach 2:
The composite filler system combines copper flakes (20-80 wt%) that provide conductivity network through extensive contacting points with copper nanoparticles (80-20 wt%) that enable low-temperature sintering. The flake particles create conductive pathways with multiple contact points, while the nanoparticle component reduces the overall sintering temperature requirement. This composite structure simultaneously achieves high conductivity and low processing temperature.
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 enables the production of conductive pastes that can be sintered at lower temperatures, minimizing substrate damage and enhancing the conductivity of printed films while improving product concentration and recovery rates.
Implementation Method 1
Copper nanoparticles exhibiting melting point depression allows the paste to be sintered at a lower temperature
Implementation Method 2
The paste precursor is brought at an elevated temperature to remove the low boiling point solvent
Data Source
AI summary
Monodispersed metal nanoparticles are prepared by preparing a homogeneous metal complex solution by mixing metal salt with a complexing agent in solvent. A precipitating agent is added into the homogeneous metal complex solution to form a slurry. A homogeneous mixture of reducing agent and solvent is added to perform reducing reaction on the slurry to form metal nanoparticles in a controlled environment under gas purge. A capping agent is added to modify surface properties of metal nanoparticles. The metal nanoparticles are washed and the metal nanoparticles are recovered by phase extraction or centrifugation. The technique can be used to prepare conductive pastes with bimodal particle size distribution.