Densely Packed Phosphor Layer for LED Thermal Management

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Solution Overview

Problem

Conventional LED packages with uniformly distributed phosphor particles suffer from poor heat dissipation due to low thermal conductivity, leading to phosphor self-heating and reduced efficiency, especially at higher flux densities.

Innovation Solution

A densely packed layer of phosphor particles is arranged at the light emitting surface of the LED chip, with reduced or no phosphor particles in the coating above, and surface features or an intermediate layer to enhance direct contact and heat transfer, reducing the average distance heat travels and improving thermal conductivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If phosphor particles are uniformly distributed in the encapsulant coating, then the coating provides adequate optical coverage, but heat dissipation is poor due to low thermal conductivity

Engineering Contradiction:

Improvephosphor temperatureVSAvoidheat dissipation efficiency

Core Design Contradiction:

TemperatureVSLoss of energy

Solution Approach 1:

The phosphor-containing coating is segmented into two distinct regions: a densely packed phosphor layer at the light emitting surface, and a phosphor-free or phosphor-depleted upper coating region. This segmentation allows the lower region to maximize heat transfer to the chip while the upper region provides optical functions with reduced heat generation

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the coating are given different phosphor concentrations optimized for their specific functions: the lower region near the chip has high phosphor density for efficient light conversion and heat dissipation, while the upper region has reduced or zero phosphor content to minimize heat generation and allow optical processing

Inventive Principle:

Principle #3Local quality

2Loss of energy

If phosphor particles are densely packed at the light emitting surface, then heat transfer to the chip is enhanced, but the coating structure becomes more complex

Engineering Contradiction:

Improveheat transfer efficiencyVSAvoidcoating structure complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The phosphor particles are caused to settle and form a densely packed layer at the light emitting surface before the coating is cured. This preliminary settling action (achieved through viscosity reduction and gravity/centrifugal force) creates the desired thermal management structure in advance, simplifying the overall manufacturing process

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The viscosity of the phosphor-containing coating material is temporarily reduced (by heating or adding solvent) to allow phosphor particles to settle under gravity or centrifugal force, then the viscosity is increased again by curing to lock in the densely packed configuration. This parameter change enables simple process steps to achieve complex structural outcomes

Inventive Principle:

Principle #35Parameter changes

3Use of energy by moving object

If the coating thickness is increased to provide adequate optical coverage, then more phosphor is available for light conversion, but the average distance heat travels increases reducing heat dissipation

Engineering Contradiction:

Improvelight conversion efficiencyVSAvoidheat dissipation distance

Core Design Contradiction:

Use of energy by moving objectVSTemperature

Solution Approach 1:

The coating structure provides high phosphor concentration locally at the light emitting surface where heat generation occurs, ensuring efficient heat transfer to the chip. The upper regions have reduced phosphor content, creating a gradient that optimizes both light conversion near the chip and optical performance farther away

Inventive Principle:

Principle #3Local 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 configuration significantly enhances heat transfer between phosphor particles and the chip, reducing phosphor temperature and maintaining efficiency even at high flux densities, thereby improving the overall performance of the LED device.

Implementation Method 1

The phosphor particles absorb light having shorter wavelengths and re-emit light having longer wavelengths. As such, some or all of the light emitted by the LED chip at a first wavelength may be absorbed by the phosphor particles, which may responsively emit light at a second wavelength.

Methodology Applied

Scientific EffectPhotoluminescence: Photoluminescence

Implementation Method 2

This configuration significantly enhances heat transfer between phosphor particles and the chip, reducing phosphor temperature and maintaining efficiency even at high flux densities

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Data Source

PatentUS8884510B2Semiconductor light emitting devices with densely packed phosphor layer at light emitting surface

Publication Date: 2014.11.11 CREELED INC

AI summary

An LED includes a chip having a light emitting surface, and a coating of phosphor-containing material on the light emitting surface. The phosphor-containing material comprises at least two quantities of different phosphor particles and are arranged in a densely packed layer within the coating at the light emitting surface. The densely packed layer of phosphor particles does not extend all the way through the coating.