Fluidic Assembly of Emissive Displays via High-Variance Forcing
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Solution Overview
Problem
Conventional fluidic assembly processes face challenges in distributing microcomponents over large scales, integrating them with circuitry, and repairing defective components, particularly due to issues with velocity control, uniformity, and reliable electrical connections, which are time-consuming and costly.
Innovation Solution
The method employs high-variance local forcing to control the velocity of microcomponents, allowing them to settle into wells efficiently and maintain correct orientation, using a solder fluxing agent and auxiliary mechanisms like brushes for distribution, enabling high-speed and low-cost assembly of emissive elements like LEDs without additional metallization steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional pick-and-place process is used to transfer LED microstructures, then mechanical and electrical connections can be made, but the assembly process takes several hours to complete for displays with millions of elements
Solution Approach 1:
The patent employs fluidic transport to carry microcomponents across the substrate, using liquid flow fields to enable high-speed self-alignment and placement. This hydraulic approach replaces mechanical pick-and-place operations, achieving assembly rates of millions of devices per hour while maintaining reliable connections through controlled fluid dynamics and capillary forces at the liquid-solid interfaces.
2Reliability
If fluidic self-assembly is performed by surface energy minimization at molten solder capillary interfaces, then mechanical and electrical connections are made during assembly, but distribution of microcomponents over large scales and velocity control remain challenging
Solution Approach 1:
The patent systematically varies fluid flow parameters (velocity, pressure, flow patterns) across different regions of the substrate to control microcomponent distribution and settling. By adjusting these parameters spatially and temporally, the system achieves uniform placement density and precise positioning without complex control mechanisms, resolving the contradiction between connection reliability and control complexity.
3Reliability
If additional metallization steps and photolithography are used for electrical integration, then reliable electrical connections are achieved, but the process becomes time-consuming and costly
Solution Approach 1:
The patent merges the electrical connection formation with the mechanical assembly process by using molten solder capillary interfaces that simultaneously create both mechanical bonding and electrical conductivity. This combined approach eliminates separate metallization and photolithography steps, achieving reliable electrical connections while dramatically reducing integration time and process complexity.
4Area of stationary object
If conventional assembly processes are used for large-area arrays, then coverage is achieved, but uniformity of distribution and velocity control deteriorate over large scales
Solution Approach 1:
The patent divides the large substrate into multiple flow zones with independently controlled fluid parameters, allowing precise local control of microcomponent distribution and velocity. This segmented approach maintains uniformity across the entire large-area substrate by optimizing each zone's flow characteristics, preventing the deterioration of distribution uniformity that occurs in conventional single-zone processes.
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 achieves an assembly rate of over 56 million devices per hour with reliable electrical connections, suitable for large-area arrays, and allows for efficient repair of defective components by minimizing process steps and avoiding contaminating photolithography.
Implementation Method 1
capturing the emissive elements in the wells
Implementation Method 2
surface energy minimization at molten solder capillary interfaces
Implementation Method 3
solder fluxing agent
Implementation Method 4
annealing the substrate
Implementation Method 5
auxiliary mechanisms like brushes for distribution
Data Source
Figure 1
Figure 2A~2B
Figure 3~4B
AI summary
Fluidic assembly methods are presented for the fabrication of emissive displays. An emissive substrate is provided with a top surface, and a first plurality of wells formed in the top surface. Each well has a bottom surface with a first electrical interface. Also provided is a liquid suspension of emissive elements. The suspension is flowed across the emissive substrate and the emissive elements are captured in the wells. As a result of annealing the emissive substrate, electrical connections are made between each emissive element to the first electrical interface of a corresponding well. A eutectic solder interface metal on either the substrate or the emissive element is desirable as well as the use of a fluxing agent prior to thermal anneal. The emissive element may be a surface mount light emitting diode (SMLED) with two electrical contacts on its top surface (adjacent to the bottom surfaces of the wells).