Cantilever LED Electrodes for Stable Micro-LED Board Mounting
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Solution Overview
Problem
Small-sized LEDs used in display apparatuses for devices like smart watches and AR glasses are difficult to mount on circuit boards due to their small size and thermal expansion coefficient differences, leading to electrical connection failures and challenges in replacing defective LEDs.
Innovation Solution
The use of light emitting devices with cantilever electrodes having a fixed and free-standing edge, made of metal layers with different thermal expansion coefficients, which allows for stable electrical connection and secure mounting on a circuit board, along with an adhesive layer to prevent separation and improve pixel area efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If small-sized LEDs are transferred in a group onto a circuit board, then productivity is improved, but reliability deteriorates due to electrical connection failures caused by thermal expansion coefficient differences
Solution Approach 1:
The patent segments the electrical connection function into two parts: a rigid electrode pad on the LED chip and a flexible cantilever electrode on the circuit board. This segmentation allows the rigid LED electrode to maintain its structural integrity while the flexible cantilever electrode absorbs thermal expansion mismatches, enabling both group transfer efficiency and connection reliability.
Solution Approach 2:
The patent changes the physical parameters of the electrode structure by introducing a cantilever configuration with specific flexibility characteristics. The cantilever electrode's flexibility parameter is optimized to accommodate thermal expansion differences while maintaining electrical contact, resolving the contradiction between group transfer capability and connection stability.
2Device complexity
If sub-pixels are arranged on a two-dimensional plane, then device complexity is reduced, but area efficiency deteriorates leading to reduced luminous area and brightness
Solution Approach 1:
The patent transitions from a two-dimensional planar arrangement to a three-dimensional stacked structure. Multiple sub-pixels (red, green, blue) are arranged vertically in stacks rather than horizontally in planes, allowing the pixel array to utilize the third dimension. This dimensionality change increases the effective luminous area within the same footprint while maintaining structural simplicity.
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
Enables reliable transfer and electrical connection of small-sized LEDs in groups onto circuit boards, enhancing pixel brightness and reducing defects by maintaining stable connections and increasing the luminous area of sub-pixels in restricted spaces.
Implementation Method 1
the cantilever electrode may include at least two metal layers having different thermal expansion coefficients from each other
Data Source
AI summary
A display apparatus including a circuit board, at least one LED stack configured to emit light, electrode pads disposed on the at least one LED stack and electrically connected to the at least one LED stack, and electrodes disposed on the electrode pads and electrically connected to the electrode pads, respectively, in which each of the electrodes has a fixed portion that is fixed to one of the electrode pads and an extending portion that is spaced apart from the one of the electrode pads, and the electrodes include at least two metal layers having different thermal expansion coefficients from each other.