Conformal Phosphor Coating for LED Color Uniformity
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Solution Overview
Problem
Conventional methods for applying phosphor and other optical materials to semiconductor light emitting diodes (LEDs) face challenges such as increased cost, complexity, clumping, dripping, settling, and stratification, leading to reduced conformity and uniformity, particularly in achieving consistent white light emission.
Innovation Solution
A conformal phosphor coating is applied to LEDs, featuring a first portion on the surface and a second portion extending as a wing around the edge, with different light conversion properties in each portion, and applied in varying thicknesses based on emission characteristics, allowing for uniform light emission across different angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional dispensing methods are used to apply phosphor-containing encapsulant material over the LED, then the LED can be covered with phosphor material, but the geometry and thickness of the phosphor layer cannot be controlled, resulting in non-uniform color temperature as a function of viewing angle
Solution Approach 1:
The patent applies different phosphor materials with different color temperatures to different regions of the LED surface. Specifically, a first phosphor material with a first color temperature is applied to a first region, while a second phosphor material with a second color temperature is applied to a second region. This local differentiation allows the LED to emit uniform color temperature light across different viewing angles by compensating for the varying path lengths light travels through the phosphor layer at different angles.
Solution Approach 2:
The patent changes the parameter of color temperature by using different phosphor materials with different color temperature characteristics in different regions. This parameter variation across the LED surface enables compensation for viewing angle effects, achieving uniform perceived color temperature from all angles.
2Illumination intensity
If multiple LEDs are combined to produce white light, then polychromatic light can be generated, but the device cost, size, complexity and heat generation increase
Solution Approach 1:
The patent merges multiple phosphor materials onto a single LED chip surface, allowing one LED to perform the function that would otherwise require multiple LEDs. By combining first and second phosphor materials with different color temperatures on the same LED, the device achieves polychromatic white light output while reducing overall device complexity, size, and heat generation compared to using multiple separate LEDs.
Solution Approach 2:
The single LED chip is given multi-functionality by applying multiple phosphor materials to it, enabling one device to replace what would traditionally require multiple specialized LEDs. The LED chip universally handles both color conversion functions through the different phosphor materials, simplifying the overall system architecture.
3Quantity of substance
If droplet deposition systems are used to spray phosphor-containing material, then coating can be applied, but clumping, dripping, settling, and stratification occur, reducing conformity and uniformity
Solution Approach 1:
The patent employs a spray deposition system that utilizes pneumatic principles to atomize and distribute phosphor-containing material uniformly across the LED surface. The spray method, when properly controlled, prevents clumping and stratification by delivering material in fine, evenly distributed droplets that settle uniformly, achieving both adequate material coverage and high coating uniformity.
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 conformal coating enhances the uniformity and consistency of light emission, reducing color temperature variations and improving the reproducibility of LEDs with similar emission characteristics, while maintaining structural integrity at high temperatures.
Implementation Method 1
The phosphor material absorbs and 'downconverts' some of the blue light generated by the LED. That is, the phosphor material generates light, such as yellow light, in response to absorbing the blue light.
Implementation Method 2
The conformal coating enhances the uniformity and consistency of light emission, reducing color temperature variations
Data Source
AI summary
Methods are disclosed including applying a conformal coating to multiple light emitters. The conformal coating forms in gap areas between adjacent ones of the light emitters. The plurality of light emitters are separated into individual light emitters. The individual light emitters include the conformal coating that extends to a space corresponding to respective gap areas. Light emitting structures are disclosed including a semiconductor light emitting diode (LED) having an active region and a conformal coating including a first portion and a second portion, the first portion corresponding to at least one surface of the LED and the second portion extending from the first portion.