LED Operational Yield via Photo-Curable Elastomer Deposition
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Solution Overview
Problem
Current LED manufacturing techniques do not guarantee perfect yields, resulting in non-operational LEDs being transferred to display substrates during assembly, which can lead to defective displays.
Innovation Solution
A process involving a conductive surface and photo-sensitive polymers is used to differentiate operational from non-operational LEDs by applying a voltage difference, causing operational LEDs to emit light and cure a polymer layer, while non-operational LEDs do not, allowing a pick-up tool to selectively pick up only operational LEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current LED manufacturing techniques are used, then production speed and volume are maintained, but non-operational LEDs are transferred to display substrates causing defects
Solution Approach 1:
The patent applies preliminary action by depositing the photo-sensitive polymer layer on all LEDs before the pick-and-place process. This allows operational status to be determined and differentiated in advance through light exposure, enabling the PUT to selectively pick only operational LEDs while maintaining high assembly throughput without rework or rejection steps.
Solution Approach 2:
The patent introduces a photo-sensitive polymer layer as an intermediary substance between the LED and the PUT. This intermediary material serves as a mediator that translates the LED's operational status into a physical state difference (cured vs. uncured polymer), enabling automatic differentiation and selective picking without direct inspection of the LED's electrical functionality during the assembly process.
2Productivity
If all LEDs are transferred without verification, then assembly speed is maximized, but defective displays are produced
Solution Approach 1:
The patent extracts the verification function from the traditional post-assembly inspection process and integrates it into the pick-and-place operation itself. By using the photo-sensitive polymer to mark operational LEDs before picking, the system extracts and removes non-operational LEDs from the transfer process entirely, ensuring only verified good LEDs are placed on displays while maintaining maximum assembly speed.
Solution Approach 2:
The patent implements self-service by allowing each LED to automatically indicate its operational status through its own light emission that cures the polymer layer. The LED itself performs the verification function by emitting light during the polymer deposition phase, eliminating the need for external inspection equipment or manual verification during the high-speed assembly process.
3Reliability
If operational LEDs are identified and separated, then 100% yield is achieved, but additional process steps are required
Solution Approach 1:
The patent merges the identification, verification, and picking functions into a single integrated process. The photo-sensitive polymer deposition and the PUT picking operation are combined such that the same light exposure that identifies operational LEDs also creates the adhesive bond for picking. This consolidation achieves 100% transfer accuracy without adding separate verification or sorting steps to the process.
Solution Approach 2:
The patent changes the physical-chemical parameter of the polymer layer from uncured to cured state through light exposure. This parameter change serves dual purposes: it identifies operational LEDs (those that emitted sufficient light to cure the polymer) and simultaneously creates the adhesive property needed for the PUT to pick them up. This single parameter change eliminates the need for multiple process steps while ensuring accurate separation of operational from non-operational LEDs.
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
Ensures that only operational LEDs are transferred to the display substrate, achieving a 100% yield of known good dies and preventing defective LEDs from being placed, thereby improving the reliability and efficiency of the assembly process.
Implementation Method 1
A voltage difference is applied across electrodes of each LED, causing the operational LEDs to emit light
Implementation Method 2
a layer of photo-sensitive polymer is deposited on a light emitting surface of each of the plurality of LEDs... the operational LEDs to emit light and selectively cure the layers of photo-sensitive polymer
Data Source
AI summary
LEDs are manufactured on a substrate layer and picked and placed using a pick-up tool (PUT) onto a target substrate. The PUT typically attaches to an LED via an elastomer layer deposited on a surface of the LED. A given batch of manufactured LEDs may contain operational LEDs as well as non-operational LEDs. In order to separate the operational and non-operational LEDs, the LEDs are placed on a unidirectional conductive film. A photo-curable polymer is deposited on a surface of each LED. A voltage difference is applied across the electrodes of each LED via the unidirectional conductive film, causing the operational LEDs to emit light and cure the photo-curable polymer to form an elastomer layer, while the polymer deposited on the non-operational LEDs will not cure. As such, the PUT will be able to pick up the operational LEDs, while being unable to pick up the non-operational LEDs.