Capillary Suspension Conductive Paste for Printed Electronics
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Solution Overview
Problem
Existing printable conductive pastes for electronic applications face issues with sedimentation and conductivity due to the use of non-volatile organic additives and polymeric stabilizers, which can deteriorate electrical properties and are difficult to completely remove during processing.
Innovation Solution
The process involves creating capillary suspensions by mixing conductive particulate solids with a primary and secondary immiscible liquid phase, forming a network of liquid bridges that stabilizes the particles without the need for additives, allowing for tunable flow behavior and high conductivity without residual impurities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If non-volatile organic additives and polymeric stabilizers are used in printable conductive pastes, then stability during storage and processing is improved, but electrical conductivity deteriorates due to residual impurities
Solution Approach 1:
The patent removes non-volatile organic additives and polymeric stabilizers from the paste formulation entirely, replacing them with a volatile secondary liquid phase that provides necessary stability during processing but evaporates completely during sintering, leaving no conductive-deteriorating residues
Solution Approach 2:
The patent changes the volatility parameter of the liquid phase from non-volatile (conventional additives) to volatile (secondary liquid phase), enabling the system to provide stability during processing through capillary forces while eliminating residual impurities that harm conductivity
2Stability of the object's composition
If non-volatile organic additives are used to stabilize particles, then sedimentation is prevented, but complete removal during processing becomes difficult
Solution Approach 1:
The patent utilizes phase transition by selecting a secondary liquid phase that transitions from liquid during processing to vapor during sintering, enabling complete removal of the stabilizing agent and elimination of residual impurities that would otherwise remain in the fired paste
Solution Approach 2:
The secondary liquid phase serves as a temporary, disposable stabilizing agent that performs its function during processing and then completely evaporates, leaving no persistent residues in the final product
3Device complexity
If conventional printing equipment is used, then manufacturing complexity is reduced, but achieving fine lines with high aspect ratios becomes difficult due to insufficient shear thinning
Solution Approach 1:
The patent modifies the rheological parameters of the paste by incorporating a secondary liquid phase that enhances shear thinning behavior, allowing the paste to flow easily during printing (low viscosity) and then maintain fine line structures (high viscosity after deposition), enabling high aspect ratio lines with conventional equipment
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
This approach results in highly conductive layers with conductivity twice that of commercial materials, maintaining stability during storage and processing, and enabling the production of fine lines with high aspect ratios, while eliminating the need for non-volatile organic additives.
Implementation Method 1
mixing of 5 to 40 volume percent, preferably 25 to 35 volume percent, of a conductive particulate solid, 50 to 94.5 volume percent, preferably 58 to 72 volume percent, of a liquid primary phase, and 0.5 to 10 volume percent, preferably 1 to 7 volume percent, of a liquid secondary phase, in each case related to the total volume of the resulting suspension, with the primary phase and the secondary phase being substantially immiscible with each other, forming a capillary suspension being a three-phase-system solid-liquid-liquid
Implementation Method 2
Additionally, these ternary mixtures, so-called capillary suspensions exhibit a strong degree of shear thinning, which allows for conventional coating or printing equipment to be used for application
Implementation Method 3
Finally, the secondary fluid beneficial for stability and processing of the wet paste completely evaporates during drying and sintering
Data Source
Figure 1(a)~2(b)
Figure 3(a)~3(d)
Figure 4(a)~5(b)
AI summary
The present invention relates to a process for producing highly conductive, printable pastes from capillary suspensions. In particular, the present invention makes use of the capillary suspension phenomenon to design conductive pastes for printed electronic applications, such as front side metallization of solar cells, without non-volatile, organic additives that often deteriorate electrical properties.