Compact pcLED Phosphor Structure With Thermal Conduction Paths
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Solution Overview
Problem
Phosphor-converted light emitting diodes (pcLEDs) face limitations in heat dissipation and reliability due to low thermal conductivity of silicone matrices, leading to high temperatures and reduced quantum efficiency in high-power applications, where the fraction of power converted into heat can be as high as 20-30% of optical power.
Innovation Solution
The use of phosphor particles at high packing density on a transparent substrate with an inorganic non-absorbing coating for mechanical stabilization and thermal conductivity, combined with a thin silicone glue layer for optical and mechanical coupling to the LED die, enhances heat dissipation and thermal stability, allowing for efficient optical coupling and reliable operation at higher power levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If phosphor powder material is dissolved in a silicone matrix with low volume concentration, then the phosphor layer can be easily manufactured, but the thermal conductivity is low leading to high temperatures and reduced reliability
Solution Approach 1:
The patent uses a composite structure consisting of phosphor particles dispersed in a transparent polymer matrix with added inorganic particles having high thermal conductivity. This composite material combines the optical properties of the polymer with the thermal conductivity of inorganic particles, enabling efficient heat dissipation while maintaining ease of manufacture through conventional mixing and curing processes
Solution Approach 2:
The patent introduces inorganic particles with high thermal conductivity specifically into regions where heat dissipation is needed most - within the phosphor layer and at the interface with the substrate. This local enhancement of thermal conductivity addresses the heat dissipation problem without requiring complete restructuring of the entire device
2Power
If phosphor particles are used at high power levels, then light output is increased, but heat dissipation becomes insufficient leading to temperature rise and quantum efficiency decrease
Solution Approach 1:
The patent introduces inorganic particles as thermal intermediaries within the phosphor layer. These particles act as heat transfer mediators, conducting heat away from the phosphor particles and distributing it to the substrate and surrounding structures, thereby enabling high power operation without excessive temperature rise
Solution Approach 2:
The patent replaces reliance on the low thermal conductivity of the polymer matrix with a thermally conductive network formed by inorganic particles. This substitution creates efficient thermal pathways that bypass the thermal resistance of the polymer, enabling effective heat dissipation at high power levels
3Ease of manufacture
If silicone matrix is used to disperse phosphor particles, then the phosphor layer is easy to fabricate, but the low thermal conductivity of silicone causes heat accumulation and silicones discolor at high temperatures
Solution Approach 1:
The patent creates a composite material system where inorganic particles with high thermal conductivity are dispersed in the silicone matrix. This composite maintains the ease of fabrication provided by the silicone while adding efficient thermal conduction pathways that prevent heat accumulation and reduce thermal degradation
Solution Approach 2:
The patent modifies the thermal conductivity parameter of the silicone matrix by adding inorganic particles. This parameter change transforms the matrix from a thermally insulating material to a thermally conductive composite, enabling effective heat dissipation while retaining the optical and fabrication advantages of the silicone base material
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 pcLEDs to operate reliably at power levels well above 2 Watts/mm², maintaining spectral distribution and reducing heat-related issues, thereby improving reliability and efficiency.
Implementation Method 1
The particles are coated with an inorganic non-absorbing layer (e.g. Al2O3), which mechanically stabilizes the phosphor particle layers and provides a thermally conductive connection between the phosphor particles
Implementation Method 2
phosphor-converted light emitting diodes (pcLEDs) face limitations in heat dissipation and reliability due to low thermal conductivity of silicone matrices, leading to high temperatures and reduced quantum efficiency in high-power applications, where the fraction of power converted into heat can be as high as 20-30% of optical power
Data Source
AI summary
This specification discloses pcLEDs in which the wavelength converting structure comprises one or more layers of phosphor particles disposed on a transparent substrate at high packing density. The particles are coated with an inorganic non-absorbing layer which mechanically stabilizes the phosphor particle layers and provides a thermally conductive connection between the phosphor particles. The wavelength converting structure is attached to a semiconductor LED die with the transparent substrate of the wavelength converting structure facing away from the die by a thin glue layer that bonds a light emitting surface of the die to the phosphor particle layers. Methods for fabricating such pcLEDs are also disclosed.