LED Emission Tuning via Selective Phosphor Removal
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Solution Overview
Problem
Conventional methods for coating light emitting diodes (LEDs) with conversion materials, such as phosphors, face challenges in controlling the geometry and thickness of the phosphor layer, leading to non-uniform color temperature and emission characteristics, which increases manufacturing costs due to the need for binning and sorting of LEDs to achieve consistent emission characteristics within specified tolerances.
Innovation Solution
The method involves measuring the emission characteristics of LEDs, coating them with a conversion material, and selectively removing the material through micro-machining to achieve target emission characteristics, thereby reducing variations and improving color consistency across the wafer or individual LEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional coating methods (syringe/nozzle injection or stencil printing) are used to apply phosphor layer, then the LED can be coated with conversion material, but the geometry and thickness of the phosphor layer cannot be controlled uniformly, resulting in non-uniform color temperature and emission characteristics
Solution Approach 1:
The phosphor layer is deposited over the entire LED array before any individualization or coating steps. This preliminary uniform deposition ensures that all LEDs receive the same base thickness of phosphor material, which is then selectively removed or retained to achieve target emission characteristics for each LED, thereby ensuring uniformity while enabling precision control
Solution Approach 2:
After uniform preliminary coating, the phosphor layer is selectively removed or modified in specific local areas of individual LEDs based on their measured emission characteristics. This allows each LED to have a customized phosphor thickness profile while maintaining overall process uniformity, resolving the contradiction between manufacturing precision and ease of manufacture
2Ease of operation
If phosphor layer geometry and thickness are difficult to control, then coating process is simpler, but light emitted at different angles passes through different amounts of conversion material, resulting in non-uniform color temperature as a function of viewing angle
Solution Approach 1:
The invention controls the phosphor layer thickness as a critical parameter, using selective removal processes to adjust the thickness for each LED based on its emission characteristics. By precisely controlling this geometric parameter, the patent achieves uniform color temperature across different viewing angles while maintaining reasonable manufacturing precision
3Productivity
If stencil printing method is used to coat LEDs, then multiple LEDs can be coated simultaneously, but the stenciling composition may not fully fill the stencil opening or may stick to the stencil, reducing the amount of composition remaining on the LED and making it difficult to control layer uniformity
Solution Approach 1:
The phosphor composition is deposited over the entire LED array in a single preliminary step before any individualization or selective coating steps. This ensures all LEDs receive a uniform base layer of phosphor material, achieving both high productivity through simultaneous processing and precision through uniform initial deposition
Solution Approach 2:
After the uniform preliminary deposition, excess phosphor material is selectively removed from specific areas of individual LEDs based on their emission characteristics. This extraction process allows precise control of the final phosphor thickness while maintaining the benefits of the initial uniform high-throughput deposition
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 enables a high yield of LEDs with emission characteristics within a specific range, such as a 4-step MacAdam ellipse, reducing manufacturing costs and improving customer acceptance by ensuring consistent color output.
Implementation Method 1
coating the LEDs with a conversion material so that at least some light from the LEDs passes through the conversion material and is converted
Data Source
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AI summary
A method for fabricating light emitting diode (LED) chips comprising providing a plurality of LEDs, typically on a wafer, and coating the LEDs with a conversion material so that at least some light from the LEDs passes through the conversion material and is converted. The light emission from the LED chips comprises light from the conversion material, typically in combination with LED light. The emission characteristics of at least some of the LED chips is measured and at least some of the conversion material over the LEDs is removed to alter the emission characteristics of the LED chips. The invention is particularly applicable to fabricating LED chips on a wafer where the LED chips have light emission characteristics that are within a range of target emission characteristics. This target range can fall within an emission region on a CIE curve to reduce the need for binning of the LEDs from the wafer. The emission characteristics of the LED chips in the wafer can be tuned to the desired range by micro-machining the conversion material over the LEDs.