Phosphor Coating on LED Chip Surface for Color Uniformity
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Solution Overview
Problem
Existing light emitting devices with phosphor wavelength conversion suffer from non-uniform color/correlated color temperature (CCT) emission due to varying path lengths of light through the phosphor/polymer encapsulation and uneven phosphor distribution, leading to color inconsistencies across the light emitting surface, particularly when optical components like lenses are used.
Innovation Solution
A method of coating a mixture of phosphor material and light transmissive polymer material onto the light emitting surface of LED chips, ensuring a uniform thickness layer that matches the size of the light emitting surface, thereby approximating a point light source and improving color uniformity, using either thermosetting or UV curable materials with controlled temperature and volume to achieve this.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the cup is filled with phosphor/polymer mixture to cover the LED chip, then the LED chip surface is fully covered, but the light path length varies across the emission surface causing color non-uniformity
Solution Approach 1:
The patent extracts the phosphor/polymer mixture from the cup cavity and applies it directly onto the LED chip surface. This eliminates the cup structure that caused varying light path lengths, as the phosphor is now confined to a uniform thickness on the chip surface rather than filling a deep cavity with inclined walls.
Solution Approach 2:
The patent transitions from a three-dimensional cup cavity structure to a two-dimensional surface coating on the LED chip. By applying the phosphor/polymer mixture as a thin layer on the chip surface rather than filling a volumetric cup, the light path length becomes uniform across the emission area.
2Manufacturing precision
If phosphor/polymer mixture is dispensed in liquid form, then it flows to cover the surface, but it accumulates at edges and on bond wires causing uneven distribution
Solution Approach 1:
The patent changes the physical state parameter of the phosphor/polymer mixture from liquid to paste form. This viscosity modification prevents the mixture from flowing freely and accumulating at edges and on bond wires, while still allowing it to be dispensed and spread into a uniform coating on the LED chip surface.
3Illumination intensity
If the phosphor layer thickness is increased to improve color conversion, then more blue light is converted to yellow, but the device size and light path variation increase
Solution Approach 1:
The patent maintains a thin phosphor layer by applying it as a surface coating rather than filling a deep cup cavity. This two-dimensional surface application allows sufficient phosphor thickness for color conversion while preventing the excessive light path length that would occur with a volumetric fill, thus avoiding color non-uniformity.
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 results in improved color uniformity and reduced manufacturing complexity by ensuring a uniform phosphor distribution, enhancing the reliability and efficiency of light emitting devices with phosphor wavelength conversion.
Implementation Method 1
white LEDs include one or more phosphor materials, that is photo-luminescent materials, which absorb a portion of the radiation emitted by the LED and re-emit radiation of a different color (wavelength)
Implementation Method 2
heating the light emitting diode chip package assembly to a pre-selected temperature; and dispensing a pre-selected volume of a mixture of at least one phosphor and a light transmissive thermosetting material
Implementation Method 3
after a pre-selected time irradiating the phosphor material mixture with UV radiation
Data Source
AI summary
A method of fabricating a light emitting device comprises: mounting a light emitting diode chip in a package; heating the light emitting diode chip package assembly to a pre-selected temperature; and dispensing a pre-selected volume of a mixture of at least one phosphor and a light transmissive thermosetting material (silicone, epoxy) on a surface of the chip. The pre-selected volume and temperature are selected such that the phosphor/material mixture flows over the entire light emitting surface of the chip before curing. In an alternative method, using a light transmissive UV curable material such as an epoxy, the phosphor/material mixture is irradiated with UV radiation after a pre-selected time to cure the material. The pre-selected volume and pre-selected time are selected such that the phosphor/material mixture flows over at least the light emitting surface of the chip before curing.