Wafer-Level LED Color Correction Using Spacer-Controlled Phosphor Thickness
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Solution Overview
Problem
Conventional methods for coating light-emitting diodes (LEDs) with conversion materials, such as phosphors, at the wafer level face challenges in controlling geometry and thickness, leading to non-uniform color temperature and emission characteristics, which increases manufacturing costs due to the need for binning and sorting of LEDs by color and brightness.
Innovation Solution
The use of spacers on LEDs before applying a conversion material coating, which reduces the amount of conversion material needed, allowing LEDs to emit light within a standard deviation of a target wavelength, thereby reducing variations in emission characteristics across a wafer and eliminating the need for multiple bins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional coating methods (syringe or stencil) are used to apply phosphor to LEDs, then the coating process is simple to implement, but the phosphor layer geometry and thickness cannot be controlled uniformly, resulting in non-uniform color temperature and emission characteristics
Solution Approach 1:
The patent applies preliminary action by forming spacers on the LED surface before phosphor coating. These spacers pre-establish the desired phosphor layer thickness and geometry, allowing uniform phosphor deposition without complex coating process control. The spacers are formed in advance using standard semiconductor fabrication techniques, then the phosphor is simply deposited over them, eliminating the need for precise syringe or stencil positioning.
Solution Approach 2:
The patent uses spacers as an intermediary element between the LED surface and the phosphor coating. These spacers act as a template or mediator that defines the phosphor layer geometry and thickness, translating the desired final structure into a controllable fabrication process. The spacers mediate the interaction between the coating process and the LED surface, ensuring uniform results without requiring complex process control.
2Reliability
If syringe or stencil methods are used for phosphor coating, then the equipment and process are easy to implement, but it is difficult to consistently reproduce LEDs with the same emission characteristics
Solution Approach 1:
The spacers are formed in advance using standard semiconductor fabrication techniques, which are highly reliable and reproducible. This preliminary formation of spacers ensures that each LED receives the same controlled amount and geometry of phosphor coating, leading to consistent emission characteristics across all LEDs while maintaining ease of manufacture through standard processes.
Solution Approach 2:
The patent changes the fundamental parameter of how phosphor thickness is controlled - instead of relying on coating process parameters (syringe flow rate, stencil distance), the control is shifted to spacer formation parameters (spacer material deposition thickness, spacer pattern dimensions). These parameters are more easily controlled and reproduced using standard semiconductor fabrication techniques, improving both reliability and ease of manufacture.
3Productivity
If uniform phosphor coating is applied across the wafer, then the coating process is simple, but LEDs with different emission characteristics require binning and sorting, increasing manufacturing costs
Solution Approach 1:
The patent applies local quality by forming spacers with different geometries or materials in different regions of the wafer, or on different LEDs, to compensate for local variations in LED emission characteristics. This allows each LED to receive a customized phosphor coating thickness or composition through the spacer template, enabling uniform final emission across the wafer without binning, thereby improving productivity and phosphor usage efficiency.
Solution Approach 2:
By performing preliminary characterization of LED emission characteristics and forming corresponding spacers before phosphor coating, the patent enables a single-pass coating process that produces uniformly performing LEDs. This eliminates the need for post-coating binning and sorting operations, improving manufacturing efficiency and reducing phosphor waste from rejected devices.
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 results in LEDs that emit light closer to a target color point or wavelength, reducing manufacturing costs and improving the consistency of LED emission characteristics, allowing for wider acceptance in commercial lighting applications.
Implementation Method 1
The spacers reduce the amount of conversion material over the LEDs
Implementation Method 2
The surrounding phosphor material 'downconverts' the wavelength of some of the LED's blue light, changing its color to yellow
Data Source
AI summary
A method for fabricating a plurality of LED chips comprises providing a plurality of LEDs and forming a plurality of spacers each of which is on at least one of the LEDs. Coating the LEDs with a conversion material, each of the spacers reducing the amount of conversion material over its one of the LEDs. This reduction causes the plurality of LED chips to emit a wavelength of light in response to an electrical signal that is within a standard deviation of a target wavelength. LEDs, LED chips and LED chip wafers are fabricated using the method according to the present invention. One embodiment of an LED chip wafer according to the present invention comprises a plurality of LEDs on a wafer and a plurality of a spacers, each of which is on a respective one of the LEDs. A conversion material at least partially covers the LEDs and spacers, with at least some light from the LEDs passing through the conversion material and is converted. The spacers cause the LED chips to emit light having a wavelength within a standard deviation compared to the similar LED chips without the spacers where at least some of the LED chips emit light a wavelength of light outside the standard deviation.