LED Color Point Control via Selective Phosphor Deposition
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Solution Overview
Problem
Conventional methods for fabricating semiconductor light emitting devices result in inconsistent emission of white light due to variations in electrical and optical parameters, leading to a wide color point variance in packaged LEDs, which can be outside the desired MacAdam ellipse, affecting yield and quality.
Innovation Solution
A method involving the measurement of emission characteristics of LED chips, sorting them into groups with similar characteristics, and selectively applying light conversion materials to achieve a desired color point, with the option of varying the thickness and type of phosphor materials based on average wavelengths and radiant flux to ensure the packaged LEDs emit light within a tighter color tolerance, such as a 4-step MacAdam ellipse.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional methods are used to deposit the same light conversion material on all LED chips, then the manufacturing process is simple and fast, but the color point variance is wide and inconsistent white light emission results
Solution Approach 1:
The patent segments LED chips into different groups based on their emission characteristics (wavelength, radiant flux). Each group receives a customized light conversion material selection and deposition thickness, rather than applying a uniform approach to all chips. This segmentation enables precise color point control while maintaining manufacturing efficiency.
Solution Approach 2:
The patent implements local quality by tailoring the light conversion material properties (type, thickness, concentration) to match the specific emission characteristics of each LED chip group. Chips with different wavelengths or radiant flux values receive different phosphor formulations, ensuring that each local region (chip group) achieves the target color point optimally.
2Reliability
If LED chips with varying emission characteristics are packaged without sorting, then productivity is high and manufacturing is fast, but yield and quality are reduced due to color point variance outside MacAdam ellipse
Solution Approach 1:
The patent performs preliminary measurement and sorting of LED chips into groups based on their emission characteristics before the light conversion material deposition step. This preliminary classification ensures that subsequent processing can be optimized for each group, improving final product quality and yield without significantly impacting overall manufacturing speed.
Solution Approach 2:
The patent changes key parameters (light conversion material type, deposition thickness, phosphor concentration) based on the measured emission characteristics of each LED chip group. By adjusting these parameters according to wavelength and radiant flux variations, the process achieves consistent color point output across all chips, thereby improving yield and quality.
3Manufacturing precision
If a fixed thickness of light conversion material is deposited on all LED chips, then the manufacturing process is simple and productive, but color point consistency cannot be achieved due to variations in LED chip emission characteristics
Solution Approach 1:
The patent introduces dynamics into the manufacturing process by making the light conversion material deposition thickness variable rather than fixed. The deposition parameters are dynamically adjusted based on the measured emission characteristics of each LED chip group, allowing the process to adapt to variations in wavelength and radiant flux while maintaining color point precision.
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 approach ensures that packaged LEDs emit light with a consistent color point within a tighter tolerance, improving yield and reducing color variance, allowing for the production of LEDs that target specific color points with higher precision and consistency.
Implementation Method 1
phosphors absorb light having shorter wavelengths and re-emit light having longer wavelengths. At least some of the light emitted by the LED chip at a first wavelength (primary light) may be absorbed by the phosphor, which may responsively emit light at a second wavelength (secondary light)
Implementation Method 2
a sensor configured to measure emission characteristics of light emitted by the LED structure
Data Source
AI summary
A method of fabricating a light emitting device (LED) includes measuring emission characteristics for a plurality of LED chips configured to emit light of a first color. The plurality of LED chips are sorted based on the measured emission characteristics to provide a plurality of groups respectively including ones of the plurality of LED chips having similar measured emission characteristics. A respective light conversion material is selected for each of the plurality of groups based on the measured emission characteristics of the ones of the plurality of LED chips included therein and a desired color point. The selected light conversion material is configured to absorb at least some of the light of the first color and responsively emit light of a second color. For each of the plurality of groups, the respective selected light conversion material is deposited on the ones of the LED chips included therein to provide a plurality of packaged LEDs including the plurality of LED chips and respectively configured to emit light having the desired color point. Related apparatus is also discussed.