Mini LED DBR Stack Structure for AOI-Compatible Light Reflection
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Solution Overview
Problem
Mini LEDs with a distributed Bragg reflector (DBR) stack structure on their back surface often fail automated optical inspection (AOI) testing, leading to decreased testing yield, despite good soldering conditions.
Innovation Solution
The LED design includes a substrate with a semiconductor stack layer for light emission and a DBR stack structure on the opposite surface, composed of repeatedly stacked first and second material layers. The DBR stack structure is optimized to reflect small-angle light emissions and transmit large-angle light emissions, with a reflectivity of at least 40% for wavelengths corresponding to its color, allowing it to pass through AOI testing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a DBR stack structure is added to the back surface of the Mini LED to improve light-emitting angle and prevent light leakage, then brightness and light-emitting efficiency are improved, but the LED fails AOI testing due to light reflection
Solution Approach 1:
The patent applies different optical properties to different regions of the DBR structure by controlling the thickness of individual layers. The first DBR layer has a thickness designed for high reflectivity to prevent light leakage, while the second DBR layer has a different thickness that provides both reflection for brightness enhancement and transmission in the 480-550nm wavelength range for AOI testing compatibility. This local differentiation of optical properties resolves the contradiction between brightness improvement and AOI testing pass rate.
Solution Approach 2:
The patent changes the optical parameters of the DBR structure by precisely controlling the thickness of each layer. The first DBR layer thickness is set to reflect most light for brightness enhancement, while the second DBR layer thickness is specifically optimized to transmit light in the 480-550nm wavelength range, allowing AOI testing to pass. This parameter optimization resolves the contradiction between improving illumination intensity and maintaining reliability in AOI testing.
2Stability of the object's composition
If the DBR layer is plated on the back surface to enable oblique light emission at large angles, then overall uniformity of light-emitting length is improved, but testing yield decreases due to AOI failure
Solution Approach 1:
The patent uses a two-layer DBR structure where each layer has different thickness parameters optimized for specific functions. The first layer provides uniform light emission across large angles, while the second layer introduces wavelength-selective transmission in the 480-550nm range. This local differentiation allows the system to maintain uniformity of light-emitting length while passing AOI testing, thereby resolving the contradiction between stability and productivity.
Solution Approach 2:
The patent employs a composite DBR structure consisting of two distinct layers with different optical properties. The first DBR layer and second DBR layer are combined to achieve both uniform light emission at large angles and selective light transmission for AOI compatibility. This composite approach resolves the contradiction between improving uniformity of light-emitting length and maintaining testing yield.
3Loss of energy
If a DBR stack structure is implemented to reflect small-angle light emissions, then light leakage is prevented and brightness is improved, but AOI testing is affected due to light reflection
Solution Approach 1:
The patent applies different thickness parameters to different DBR layers to create localized optical functions. The first DBR layer is designed with thickness for high reflectivity to prevent light leakage, while the second DBR layer has a different thickness that allows transmission in the 480-550nm wavelength range. This local quality differentiation resolves the contradiction between preventing energy loss through light leakage and maintaining reliability in AOI testing.
Solution Approach 2:
The patent changes the thickness parameter of the DBR layers to achieve different optical effects. The first layer thickness is optimized for reflecting small-angle light emissions to prevent light leakage, while the second layer thickness is specifically designed to transmit light in the 480-550nm range for AOI testing compatibility. This parameter optimization resolves the contradiction between reducing energy loss and maintaining AOI testing pass rate.
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 design enhances the light-emitting efficiency of Mini LEDs by preventing light leakage and improving brightness, while also ensuring that the LEDs pass AOI testing, thus increasing testing yield.
Implementation Method 1
reflecting light with any wavelength within a first wavelength range and having an incident angle within a first angle range
Implementation Method 2
a distributed Bragg reflector (DBR) structure
Implementation Method 3
transmitting a part of light with any wavelength within the first wavelength range and having an incident angle within a second angle range
Data Source
AI summary
A light-emitting diode includes a substrate, a semiconductor stack layer, a DBR stack structure that includes a first material layer and a second material layer, which are repeatedly stacked. Optical thicknesses of the first material layer and the second material layer are capable of: reflecting light within a first wavelength range and within a first angle range, transmitting a part of light within the first wavelength range and within a second angle range, where the first angle range is less than the second angle range. A reflectivity in response to light with at least one wavelength in a second wavelength range and having an incident angle of 0-10 degrees is ≥40%, the DBR stack structure has a color, and wavelengths contained in the second wavelength range are ≥ a critical wavelength of the color corresponding to the DBR stack structure through which AOI testing passes.