Copper Ink Formulation for Printed Electronics
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Solution Overview
Problem
Current copper inks for printed electronics are expensive, prone to oxidation, and lack the necessary conductivity and stability for wide-scale commercial use, particularly when used on plastic substrates and requiring thermal or photo-sintering processes.
Innovation Solution
A copper-based ink comprising copper hydroxide and diethanolamine in a specific molar ratio, which forms a complex, is developed for screen printing, allowing for thermal and photo-sintering to produce conductive copper traces with improved stability and conductivity, optionally enhanced with copper nanoparticles and silver salts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If nanoparticle-based copper inks are used, then conductivity is improved, but cost increases and oxidation resistance deteriorates
Solution Approach 1:
The patent changes the chemical parameters of the ink formulation by using copper hydroxide instead of expensive copper nanoparticles, and employs diethanolamine as a complexing agent to stabilize the copper ions. This parameter change achieves comparable conductivity while reducing cost and improving oxidation resistance through the specific chemical interactions in the formulation.
Solution Approach 2:
The invention creates a composite ink system combining copper hydroxide particles with diethanolamine molecules that form coordination complexes. This composite approach allows the material to exhibit both the conductivity needed for electronics and the oxidation resistance required for stability, while avoiding the high cost of pure copper nanoparticle inks.
2Temperature
If MOD inks are used, then sintering temperature is reduced, but copper loading decreases and conductivity deteriorates
Solution Approach 1:
The patent optimizes the copper loading parameter in the ink formulation to achieve sufficient conductivity while maintaining low sintering temperatures. By carefully controlling the copper hydroxide concentration and the diethanolamine to copper ratio, the formulation achieves a balance between metal content and processing temperature, avoiding the low conductivity issue of MOD inks while preserving the low-temperature advantage.
3Reliability
If copper loading is increased to improve conductivity, then oxidation resistance deteriorates
Solution Approach 1:
The patent introduces diethanolamine as an intermediary substance that mediates between copper ions and oxygen. The diethanolamine forms coordination complexes with copper, creating a protective chemical environment that prevents direct oxidation of copper while maintaining the electrical conductivity pathway. This intermediary approach allows high copper loading without proportional increase in oxidation damage.
4Ease of manufacture
If screen printing is used for deposition, then manufacturing cost is reduced, but ink viscosity requirements become more stringent
Solution Approach 1:
The patent adjusts the viscosity parameters of the ink by optimizing the solvent system and the concentration of copper hydroxide and diethanolamine. The formulation is specifically designed to achieve the viscosity range required for screen printing, balancing flow properties for printability with sufficient metal content for conductivity, thereby enabling low-cost manufacturing through screen printing while managing formulation complexity.
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 ink achieves high conductivity with sheet resistivity of 20 mΩ/□/mil or less for screen-printed lines, exhibits excellent resolution, and demonstrates improved air stability and adhesion strength, making it suitable for various electronic applications.
Implementation Method 1
copper hydroxide and diethanolamine form a complex in the ink
Implementation Method 2
decomposing the ink on the substrate to form a conductive copper coating
Implementation Method 3
improved air stability compared to traces produced from other copper inks
Data Source
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AI summary
A copper-based ink contains copper hydroxide and diethanolamine. The ink may be coated on a substrate and decomposed on the substrate to form a conductive copper coating on the substrate. The ink is low cost and micron-thick traces of the ink may be screen printed and thermally sintered in the presence of up to about 500 ppm of oxygen or photo-sintered in air to produce highly conductive copper features. Sintered copper traces produced from the ink have improved air stability compared to traces produced from other copper inks. Sintered copper traces having sheet resistivity of about 20 mΩ/□/mil or less may be obtained for 5-20 mil wide screen-printed lines with excellent resolution.