Wafer-Level Phosphor Coating for Uniform LED Color
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Solution Overview
Problem
Conventional methods for coating light emitting diodes (LEDs) with phosphor materials at the wafer level face challenges such as non-uniform color temperature, difficulty in accessing wire bond pads, and reduced emission efficiency due to overlapping phosphor spectra, leading to inconsistent emission characteristics and customer dissatisfaction.
Innovation Solution
The method involves sequentially coating LEDs with two or more layers of conversion materials at the wafer level, where each layer has a non-overlapping absorption and emission spectrum to minimize re-absorption losses, and using pedestals for electrical contact and precise control of phosphor thickness and distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single phosphor layer is used to convert LED light, then the coating process is simple, but the color temperature uniformity deteriorates due to varying light paths through the phosphor
Solution Approach 1:
The single phosphor layer is divided into multiple phosphor layers with different phosphor materials. Each layer converts specific wavelengths of LED light, and by controlling the thickness and composition of each layer, uniform color temperature is achieved across different viewing angles while maintaining a manageable coating process
Solution Approach 2:
Different phosphor materials are placed in different layers to optimize local light conversion properties. The first phosphor layer converts blue light to yellow, while the second phosphor layer converts blue light to red, creating localized spectral modifications that collectively produce uniform white light emission
2Manufacturing precision
If multiple phosphor layers are used to improve color uniformity, then the color temperature uniformity improves, but the device complexity increases
Solution Approach 1:
Multiple phosphor layers are combined in a sequential structure where each layer performs a specific wavelength conversion function. The first phosphor layer (yellow-converting) and second phosphor layer (red-converting) are stacked to achieve comprehensive spectral control, improving color uniformity while managing complexity through functional integration
3Ease of manufacture
If phosphors with overlapping spectra are used, then the emission efficiency deteriorates due to re-absorption losses, but the color rendering improves
Solution Approach 1:
The spectral parameters of phosphor materials are carefully selected to minimize overlap between emission and absorption bands. By choosing phosphors with complementary spectral characteristics (yellow-converting and red-converting), the patent reduces re-absorption losses while maintaining good color rendering, optimizing both efficiency and color quality
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 consistent and efficient emission characteristics across LEDs, reducing re-absorption losses and enhancing customer satisfaction by providing uniform color and brightness, while allowing for precise tuning of emission characteristics.
Implementation Method 1
The first conversion material has a first conversion material emission spectrum. The second conversion material has a second conversion material excitation spectrum and a second conversion material emission spectrum. The first conversion material emission spectrum does not substantially overlap with the second conversion material excitation spectrum.
Data Source
AI summary
Methods for wafer level fabricating of light emitting diode (LED) chips are disclosed with one embodiment of a method according to the present invention comprising providing a plurality of LEDs and then coating of the LEDs with a layer of first conversion material so that at least some light from the LEDs passes through the first conversion material. The light is converted to different wavelengths of light having a first conversion material emission spectrum. The LEDs are then coated with a layer of second conversion material arranged on the first layer of conversion. The second conversion material has a wavelength excitation spectrum, and at least some light from the LEDs passes through the second conversion material and is converted. The first conversion material emission spectrum does not substantially overlap with the second conversion material excitation spectrum. Methods according to the present invention can also be used in wafer level fabrication of LED chips and LED packages with pedestals for electrically contacting the LEDs through the conversion coatings.