Microfluidic Electrode Printing with Primer Layers for Low-Heat Sintering
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Solution Overview
Problem
Existing microfluidic devices face challenges in accurately and precisely placing electrodes relative to fluid channels, leading to variations in electric field magnitude and potential electrical short circuits, especially when using thermoplastic substrates which can be damaged by high sintering temperatures required for conductive ink drying.
Innovation Solution
A primer layer is applied to the substrate before the conductive ink, absorbing non-volatile solvents and allowing for lower temperature sintering, resulting in more uniform and reproducible conductive layers with better defined edges and fewer voids, improving the spatial control and conductivity of the electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high sintering temperature is used to dry conductive ink, then complete solvent evaporation and conductive pathway formation is achieved, but thermoplastic substrates are damaged
Solution Approach 1:
A primer layer comprising porous particles and binder is applied to the substrate before the conductive ink. This primer layer acts as an intermediary that absorbs the non-volatile solvent from the conductive ink, enabling solvent removal at lower temperatures that do not damage the thermoplastic substrate while still forming conductive pathways.
Solution Approach 2:
The primer layer utilizes porous particles with controlled pore size and distribution. These porous structures provide high surface area for absorbing the non-volatile solvent from the conductive ink, allowing efficient solvent removal at reduced temperatures without compromising the integrity of the thermoplastic substrate.
2Ease of manufacture
If conventional inkjet printing is used without primer layer, then manufacturing process is simple, but conductive layers have poor uniformity and reproducibility
Solution Approach 1:
The primer layer is applied in advance before the conductive ink printing step. This preliminary action prepares the substrate surface with optimal absorption characteristics, ensuring that subsequent conductive ink deposition results in uniform and reproducible conductive layers with well-defined edges and reduced void formation.
3Ease of operation
If high boiling point polyols are used as solvents in conductive ink, then premature drying in jetting nozzles is prevented, but sintering temperature requirements increase
Solution Approach 1:
The primer layer serves as an intermediary absorption medium that captures the non-volatile polyol solvent from the conductive ink after deposition. This allows the use of high boiling point polyols in the conductive ink formulation for reliable jetting operation, while the primer layer enables their removal at lower temperatures that protect the thermoplastic substrate.
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 use of a primer layer enhances the uniformity and reproducibility of conductive layers, enabling precise electrode placement, reducing the risk of electrical short circuits, and protecting thermoplastic substrates from overheating, thus improving the overall performance and reliability of microfluidic devices.
Implementation Method 1
A primer layer is applied to the substrate before the conductive ink, absorbing non-volatile solvents
Implementation Method 2
The sintering is normally a heating step which evaporates the solvent of the conductive ink and fuses the metal nanoparticles
Data Source
Figure 1A~1F
Figure 2A~2C
Figure 3~4
AI summary
A microfluidic device comprising: a substrate (10) having a microfluidic channel; an electrically conductive feature comprising an electrically conductive layer (20) arranged on a primer layer (16) and positioned with reference to the microfluidic channel, wherein the primer layer (16) comprises: (i) an organic polymer selected from the group consisting of: (a) a homopolymer or copolymer including a vinyl lactam repeating unit; (b) a cellulose ether; (c) polyvinyl alcohol; and (d) unmodified or modified gelatin; and (ii) a porous particulate material, the organic polymer being dispersed in the porous particulate material; is provided. Methods for manufacturing the microfluidic devices and their use in a number of applications are also provided.