Wafer Level Flip Chip LED Array Series Wiring
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Solution Overview
Problem
Existing light emitting diode (LED) arrays face challenges in being driven at high voltages, requiring submount substrates and discrete reflective metal layers, which increase fabrication costs and complexity, and can lead to light loss and reliability issues due to heat and thermal expansion differences.
Innovation Solution
A flip-chip type LED array is designed with upper electrodes connecting LEDs in series, eliminating the need for submount substrates and discrete reflective layers, using inclined side surfaces and interlayer insulating layers to prevent cracks and improve light reflection, allowing direct mounting on printed circuit boards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a submount substrate is used to connect flip-chip type LEDs in series, then the LEDs can be mounted and wired, but the fabrication cost increases and the device thickness increases
Solution Approach 1:
The patent merges the submount substrate function with the array substrate by directly forming wiring patterns on the array substrate to connect LED chips. This eliminates the separate submount substrate layer, reducing device thickness and fabrication complexity while maintaining the series connection capability between LEDs.
Solution Approach 2:
The patent extracts and removes the submount substrate from the structure by implementing direct wiring on the array substrate. This eliminates the intermediate substrate layer that adds thickness and cost, while preserving the essential electrical connection function through alternative wiring patterns formed directly on the array substrate.
2Ease of manufacture
If wire bonding is used to form wirings between electrodes, then electrical connections are established, but a molding layer must be added for protection, increasing process complexity
Solution Approach 1:
The patent replaces the mechanical wire bonding process with a planar wiring pattern formed directly on the array substrate using thin film deposition techniques. This substitution eliminates the need for wire bonding and the associated molding layer for wire protection, simplifying the manufacturing process while maintaining electrical connection functionality.
Solution Approach 2:
The patent transitions from three-dimensional wire bonding to a two-dimensional planar wiring structure formed on the substrate surface. This dimensional change eliminates the need for wire protection molding and simplifies the overall device structure by integrating connections in the plane of the substrate rather than in three-dimensional space.
3Device complexity
If lateral type LED chips are used, then the structure is simple, but light-emitting performance and heat dissipation are deteriorated
Solution Approach 1:
The patent inverts the LED chip orientation from lateral type to flip-chip type, where the light-emitting surface faces downward toward the substrate. This inversion improves heat dissipation by direct thermal contact with the substrate and enhances light extraction efficiency, while the simple planar wiring structure maintains overall device simplicity.
4Adaptability or versatility
If discrete voltage converting means are used to enable AC power source operation, then the LED can be driven, but the volume of the illuminating apparatus increases and heat is generated
Solution Approach 1:
The patent designs the LED array with series-connected LEDs that can operate at higher voltages, enabling direct compatibility with AC power sources or higher voltage DC supplies. This multi-functionality allows the same array structure to serve different power source requirements without adding discrete voltage converting means, reducing volume and heat generation.
Data Source
AI summary
A wafer level light-emitting diode (LED) array includes: a growth substrate; a plurality of LEDs arranged over the substrate, each including a first semiconductor layer, an activation layer, and a second semiconductor layer; a plurality of upper electrodes formed from a common material and electrically connected to the first semiconductor layers of the corresponding LEDs; and first and second pads arranged over the upper electrodes. The LEDs are connected in series by the upper electrodes, the first pad is electrically connected to an input LED from among the LEDs connected in series, and the second pad is electrically connected to an output LED from among the LEDs connected in series. Accordingly, a flip chip-type LED array can be provided which can be driven with a high voltage.