Micro-LED Bonding Using Flux Trapping for Single-Step Assembly
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Solution Overview
Problem
The challenge in micro-LED manufacturing lies in the difficulty of placing and bonding LEDs on substrates without damaging them, particularly due to the formation of oxide layers and the inefficiency of thermocompression bonding, which requires multiple heating cycles and is time-consuming.
Innovation Solution
The use of flux or underfill as a trapping layer between the LEDs' electrodes and the substrate contacts, allowing for temporary attachment and simultaneous bonding of multiple LEDs without external pressure, using heat to form metallic contacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thermocompression bonding is used to bond LEDs to substrate, then metallic contacts are formed between LED and substrate, but multiple heating cycles are required which increases time consumption and risk of damaging LEDs
Solution Approach 1:
The patent applies flux or underfill material to the substrate contacts before placing the LED electrodes. This preliminary application of bonding aid enables subsequent bonding to occur more efficiently, allowing multiple LEDs to be bonded simultaneously in a single heating cycle rather than requiring multiple sequential heating cycles, thus reducing time consumption while maintaining bonding quality
Solution Approach 2:
The patent combines multiple bonding operations into a single simultaneous bonding process. By using flux or underfill as a trapping layer that holds multiple LEDs in place, the system can bond multiple LEDs to the substrate in one heating cycle rather than bonding them sequentially, thereby merging multiple time-consuming operations into a single efficient process
2Reliability
If multiple heating cycles are applied to bond LEDs sequentially, then each LED can be bonded correctly, but oxide layers form at the metallic contacts and LEDs are at risk of damage
Solution Approach 1:
The patent introduces flux or underfill material as an intermediary substance between the LED electrodes and substrate contacts. This intermediary material serves multiple functions: it facilitates bonding, prevents oxide formation at the metallic contacts during heating, and protects the LED structures from thermal damage. By placing LEDs simultaneously on the substrate with this protective layer in place, harmful effects are minimized while maintaining bonding accuracy
Solution Approach 2:
The flux or underfill material is applied beforehand to the substrate contacts before LED placement. This creates a protective cushion that prevents direct exposure of the metallic contacts to oxidizing environments during heating and protects LEDs from thermal shock, thereby preventing oxide formation and LED damage before the bonding process even begins
3Reliability
If LEDs are placed one at a time and bonded sequentially, then each bonding can be controlled, but the process becomes time consuming and complex
Solution Approach 1:
The patent merges multiple sequential bonding operations into a single simultaneous bonding process. By using flux or underfill as a trapping layer that can hold multiple LEDs in correct positions, the system bonds multiple LEDs to the substrate in one heating cycle rather than bonding them sequentially, thereby merging multiple time-consuming operations into a single efficient process that maintains bonding control while dramatically improving throughput
Solution Approach 2:
The flux or underfill material serves multiple functions simultaneously: it acts as a trapping layer to hold LEDs in position, facilitates thermal transfer during bonding, prevents oxide formation, and enables simultaneous bonding of multiple LEDs. This multi-functionality allows the system to maintain bonding control while achieving high productivity through parallel processing
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 method reduces the risk of damaging LEDs, minimizes oxide formation, and streamlines the bonding process by allowing multiple LEDs to be bonded in a single step, reducing time and preventing misalignment.
Implementation Method 1
Flux or underfill is provided on at least the electrodes or the contacts... with the flux or underfill as a trapping layer between the electrodes and the contacts
Implementation Method 2
The electrodes, the contacts, and the flux or underfill are heated to form a metallic contact between the LED die and the substrate... TC bonding forms metallic contacts between two metals by simultaneously applying force and heat
Data Source
Figure 1A~1B
Figure 2A~2C
Figure 3A~3C
AI summary
Embodiments relate to using flux or underfill as a trapping layer for temporarily attaching light emitting diodes (LEDs) to a substrate and heating to simultaneously bond multiple LEDs onto the substrate. The flux or underfill may be selectively coated at the ends of electrodes of the LEDs prior to placing the LEDs on the substrate. Due to adhesive properties of the flux or underfill, multiple LEDs can be placed on and attached to the substrate prior to performing the bonding process. Once LEDs are placed on the substrate, the flux or underfill facilitates formation of metallic contacts between electrodes of the LED and contacts of the substrate during the bonding process. By using the flux or underfill, the formation of metallic contacts can be performed even without applying pressure.