Flip-Chip LED Heat Dissipation via Inverted Epitaxial Structure
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Solution Overview
Problem
LEDs with sapphire and AlN non-conductive substrates face high PN junction temperatures due to low thermal conductivity, necessitating improved heat dissipation methods for enhanced light emitting efficiency.
Innovation Solution
A flip-chip light emitting device is developed, featuring a light-emitting epitaxial laminated layer connected to a non-conductive substrate via electrodes, with external electrodes extending to form electrical connections and a plating seed layer for electroplating, allowing for efficient heat dissipation and light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sapphire and AlN non-conductive substrates are used for LED chips, then the substrate provides electrical insulation and structural support, but the low thermal conductivity of the substrate causes high PN junction temperature
Solution Approach 1:
The patent inverts the conventional LED structure by flipping the chip orientation. The p-type GaN layer that would normally be on top is now at the bottom contacting the substrate, while the n-type GaN layer is at the top. This inversion allows the highly conductive AlN buffer layer to be positioned at the substrate interface for optimal heat dissipation, while maintaining electrical insulation through the non-conductive substrate below.
Solution Approach 2:
The patent applies different material qualities to different regions: the AlN buffer layer provides high thermal conductivity at the substrate interface where heat generation is highest, while the non-conductive sapphire or AlN substrate provides electrical insulation. This local optimization of material properties resolves the contradiction between thermal management and electrical insulation requirements.
2Ease of manufacture
If conventional LED structure is used, then fabrication is straightforward, but light emitting efficiency is lower and heat dissipation is insufficient
Solution Approach 1:
By inverting the conventional LED structure, the patent achieves superior light emitting efficiency and heat dissipation performance. The flipped configuration allows the active region to be positioned optimally for light extraction while maintaining compatibility with standard fabrication processes, thus resolving the contradiction between manufacturing ease and performance improvement.
3Temperature
If flip-chip structure is adopted to improve heat dissipation, then light emitting efficiency increases, but fabrication complexity increases due to alignment requirements
Solution Approach 1:
The patent performs preliminary actions during the epitaxial growth stage by pre-forming the flipped structure with properly positioned electrodes and contact layers. This preliminary configuration eliminates the need for complex post-growth alignment operations, as the chip can be directly transferred and bonded to the substrate without precise alignment requirements, thus reducing fabrication complexity while maintaining the heat dissipation benefits of the flip-chip structure.
4Manufacturing precision
If precise chip alignment is required during fabrication, then electrode connection accuracy is improved, but fabrication efficiency decreases and package costs increase
Solution Approach 1:
The patent incorporates preliminary alignment features and pre-formed electrode structures during the epitaxial growth process. This preliminary preparation ensures that subsequent bonding operations do not require high-precision alignment, thereby maintaining electrode connection accuracy while significantly improving fabrication efficiency and reducing package costs.
Solution Approach 2:
The flipped chip structure is designed to be self-aligning during the bonding process, where the pre-formed electrodes and contact layers automatically position themselves correctly relative to the substrate contacts. This self-service alignment mechanism eliminates the need for complex external alignment systems, maintaining manufacturing precision while enhancing fabrication efficiency.
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
The flip-chip structure effectively improves heat dissipation and light emitting efficiency, reducing the risk of short circuits and electric leakage, while enabling full wafer processing without precise chip alignment, thus enhancing fabrication efficiency and lowering package costs.
Implementation Method 1
a plating seed layer is formed between the non-conductive substrate and the first and the second external electrodes. Preferably, the first and the second external electrodes are electroplated on the plating seed layer.
Implementation Method 2
For LED chips with sapphire and AlN non-conductive substrates, thermal conductivity of the substrate is low, resulting in high temperature of the PN junction in lateral LEDs. To improve heat dissipation, a flip-chip structure with higher light emitting efficiency is proposed.
Implementation Method 3
light emitting diodes (LEDs) are known as the fourth generation of lighting sources or the energy-saving lighting sources
Data Source
AI summary
A flip-chip light emitting device includes: a light-emitting epitaxial laminated layer with two opposite surfaces, in which, the first surface is a light-emitting surface; a first electrode and a second electrode that are separated from each other on the second surface of the light-emitting epitaxial laminated layer; a non-conductive substrate with two opposite surfaces and two side walls connecting those two surfaces, in which, the first surface is connected to the light-emitting epitaxial laminated layer through the first and the second electrodes; a first external electrode and a second external electrode on the second surface of the non-conductive substrate, which extend to the side walls of the non-conductive substrate till and at least cover parts of the side walls of the first and the second electrodes to form electrical connection.