Light Sintering Copper Oxide Ink for Flexible Wiring
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Solution Overview
Problem
Conductive inks using silver particles are expensive and require high-temperature thermal sintering, which increases production costs and can damage flexible printed circuit boards, while copper-based inks face issues with copper oxide film formation and high electrical resistance.
Innovation Solution
An ink composition for light sintering using copper oxide nanoparticles with a reducing agent, such as an aldehyde-based compound, and a binder, which forms a copper oxide film with a thickness of 500 nm or less, allowing for the formation of pure copper nanoparticles through light irradiation, reducing production costs and preventing board damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silver-containing conductive inks are used to form wiring patterns, then conductivity and adhesion are improved, but fabrication cost increases
Solution Approach 1:
The patent replaces expensive silver particles with inexpensive copper particles as the conductive material. The copper particles are used in a disposable ink formulation that is printed and then sintered, eliminating the need for expensive silver while maintaining functional conductivity in the finished wiring pattern.
Solution Approach 2:
The patent changes the material parameter from silver to copper, and simultaneously changes the processing parameter from high-temperature thermal sintering to low-temperature or room-temperature sintering methods. This dual parameter change enables cost reduction while maintaining wiring pattern functionality.
2Reliability
If thermal sintering process is used to form wiring patterns, then conductivity is improved, but wiring board damage occurs
Solution Approach 1:
The patent replaces the thermal sintering process (heat-based) with alternative sintering methods such as photonic sintering using lasers or flash lamps, or electric field-based sintering. This substitution eliminates the need for high-temperature exposure that damages flexible wiring boards while still achieving particle bonding and conductivity.
Solution Approach 2:
The patent fundamentally changes the temperature parameter from high-temperature thermal sintering (typically >200°C) to low-temperature or room-temperature sintering processes. This parameter change prevents thermal damage to the wiring board substrate while maintaining the sintering effect needed for conductivity.
3Ease of manufacture
If copper particles are used in conductive ink, then fabrication cost is reduced, but copper oxide film formation increases resistance
Solution Approach 1:
The patent applies preliminary protective actions by coating copper particles with protective layers (such as organic protective agents or thin metal layers) before printing. This preliminary protection prevents oxidation during storage and processing, and the protective layer is subsequently removed or reduced during the sintering process to reveal conductive copper.
Solution Approach 2:
The patent introduces intermediary substances such as reducing agents (e.g., hydrazine, hydroquinone, or ascorbic acid) that are added to the ink formulation. These intermediaries chemically reduce copper oxide formations on the particle surfaces, preventing resistance increase while allowing the use of inexpensive copper particles.
4Reliability
If high-temperature sintering is performed under inert gas atmosphere to prevent copper oxidation, then resistance is reduced, but production cost and time increase
Solution Approach 1:
The patent replaces the conventional thermal sintering process requiring inert gas atmosphere with photonic sintering using lasers or flash lamps. This substitution enables rapid sintering (reducing time from hours to seconds) without requiring oxygen-exclusion measures, as the brief exposure time prevents significant oxidation.
Solution Approach 2:
The patent employs rapid sintering methods that complete the bonding process in seconds rather than hours. This rushing through the sintering process minimizes the time window for copper oxidation to occur, eliminating the need for prolonged inert gas atmosphere while achieving low-resistance conductive paths.
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 composition reduces production costs and prevents board damage by using light sintering to form conductive copper patterns without the need for high-temperature thermal processes, achieving high aspect ratios and improved compactness and conductivity.
Implementation Method 1
a reducing agent including an aldehyde-based compound for forming copper nanoparticles by reducing copper oxidized by light irradiation
Data Source
AI summary
The present invention provides a method of fabricating a wiring board and a wiring board fabricated by the method, the method including a step of screen-printing the ink composition for light sintering on a flexible board body to form a preliminary wiring pattern, a step of drying the preliminary wiring pattern, and a step of reducing and sintering the oxidized copper of the copper oxide nanoparticles, which are included in the preliminary wiring pattern, by irradiating the dried preliminary wiring pattern with light to form a wiring pattern on the board body.