LED Phosphor Tablet Thermal Management
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Solution Overview
Problem
Current phosphor mixtures in reflective cups for LEDs have low thermal conductivity, leading to high operating temperatures, reduced light output, color shifting, and non-uniform color emission due to low viscosity and settling issues, limiting their use to low and medium current LEDs, and making it difficult to achieve consistent color across LED modules.
Innovation Solution
Pre-formed solid tablets with high thermal conductivity particles and a silicone binder are used, which are uniformly mixed and matched to a target color, then melted to encapsulate the LED die, ensuring uniform distribution and high thermal conductivity, thus maintaining consistent color and brightness across modules.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional phosphor mixture with transparent binder is used, then the mixture can be easily dispensed and filled in the reflective cup, but the thermal conductivity is very low (0.1-0.2 W/mK) causing high LED operating temperature
Solution Approach 1:
The patent uses a composite phosphor mixture comprising phosphor particles, transparent binder, and thermally conductive particles (such as aluminum oxide, aluminum nitride, or boron nitride). This composite structure combines the dispensability of the binder with the thermal conductivity of the particulate fillers, achieving both ease of operation and improved heat dissipation.
Solution Approach 2:
The patent modifies the physical and chemical parameters of the phosphor mixture by adjusting the concentration and size distribution of thermally conductive particles. By optimizing these parameters, the mixture achieves sufficient thermal conductivity while maintaining workable viscosity for dispensing operations.
2Ease of operation
If the phosphor mixture has low viscosity for easy dispensing, then it can fill voids around LED die, but phosphor particles settle to the bottom causing non-uniform color emission
Solution Approach 1:
The patent creates a multi-component system where different particles (phosphor and thermally conductive) have different sizes and densities. The mixture is designed so that smaller particles fill interstitial spaces between larger particles, creating a more uniform distribution that resists settling while maintaining low enough viscosity for dispensing.
Solution Approach 2:
The composite phosphor mixture incorporates multiple particle types with complementary properties. The combination of phosphor particles, binder, and thermally conductive particles creates a stable suspension that can be dispensed without significant particle settling, maintaining uniform color emission throughout the cured package.
3Illumination intensity
If high current/high heat LEDs are used for high brightness, then light output increases, but the low TC phosphor mixture cannot conduct heat away causing color shifting and reduced performance
Solution Approach 1:
The patent employs a composite phosphor mixture with thermally conductive particles (aluminum oxide, aluminum nitride, or boron nitride) dispersed in the binder. This composite structure provides a thermal conduction pathway that enables high current LEDs to operate at elevated brightness levels without excessive heat accumulation, preventing color shifting and maintaining performance stability.
Solution Approach 2:
The thermally conductive particles act as intermediary elements between the LED die and the reflective cup walls. These particles create thermal conduction pathways that facilitate heat transfer from the high-current LED die through the phosphor mixture to the cup, enabling effective heat dissipation while maintaining the optical properties needed for high light output.
4Manufacturing precision
If viscous phosphor mixture is dispensed repeatedly, then filling is complete, but it is difficult to maintain identical amounts causing non-uniform color from module to module
Solution Approach 1:
The patent optimizes the viscosity and flow characteristics of the phosphor mixture by adjusting binder content, particle size distribution, and particle concentration. These parameter changes enable the mixture to be dispensed in controlled, repeatable amounts through standard dispensing equipment, achieving uniform color across modules without requiring complex dispensing control systems.
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 solution allows for high brightness, high current, and high heat LEDs with consistent color emission and improved thermal management, ensuring uniform color and light output across LED modules by using pre-formed tablets with high thermal conductivity particles and a silicone binder, addressing the limitations of existing technologies.
Implementation Method 1
heat is not conducted from the LED die through the phosphor mixture and to the cup walls and base
Implementation Method 2
white light will be created by the combination of the yellow-green YAG emission and blue light leaking through the cured phosphor mixture
Implementation Method 3
The mixture is then cured
Implementation Method 4
The slurry is then cooled to harden the sheet
Data Source
Figure 1~5
Figure 6~9
AI summary
In one embodiment, a solid cylindrical tablet is pre-formed for a reflective cup containing an LED die, such as a blue LED die. The tablet comprises uniformly-mixed phosphor particles and transparent/translucent particles of a high TC material, such as quartz, in a hardened silicone binder, where the index of refraction of the high TC material is matched to that of the silicone to minimize internal reflection. Tablets can be made virtually identical in composition and size. The bulk of the tablet will be the high TC material. After the tablet is placed in the cup, the LED module is heated, preferably in a vacuum, to melt the silicone so that the mixture flows around the LED die and fills the voids to encapsulate the LED die. The silicone is then cooled to harden.