LED Package Sidewall Coating for Higher Near-Field Contrast
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Solution Overview
Problem
Existing LED packages face challenges in achieving high near-field contrast due to stray light scattered by submounts, side-scattered and reflected light from phosphor, and partial exposure of phosphor sidewalls during processing, which is detrimental for applications with primary or secondary optics.
Innovation Solution
A LED package design that includes a top emitting LED with a phosphor layer, a sacrificial layer for protection, and a light reflective material covering the sidewalls. A light absorbing layer is screen printed around the sacrificial and phosphor layers, defining a gap of 30 to 60 microns to absorb light guided through the reflective side coat, eliminate glare, and enhance contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If reflective material is used to cover LED sidewalls to minimize light waste, then light extraction efficiency is improved, but stray light and reduced near-field contrast occur due to side-scattered light and partial phosphor exposure
Solution Approach 1:
The patent divides the sidewall treatment into multiple functional segments: the lower portion is covered with reflective material to maximize light extraction, while the upper phosphor sidewall portion is left exposed or treated differently to minimize stray light generation. This segmentation allows each region to perform its optimal function without interfering with the other.
Solution Approach 2:
Different optical properties are applied to different regions of the LED package. The reflective material is selectively applied to specific sidewall regions where light extraction is most beneficial, while other regions maintain different surface characteristics to control stray light. This local differentiation optimizes both light extraction and contrast simultaneously.
2Object-affected harmful factors
If light absorbing lines are created by laser heating reflective material to increase contrast, then near-field contrast is improved, but significant light loss occurs due to penetration into the side coated material
Solution Approach 1:
The patent removes the harmful effect of deep laser penetration by extracting the light-absorbing function to a separate, dedicated layer applied only in the necessary regions. This light-absorbing layer is positioned strategically to block stray light paths without requiring deep modification of the reflective coating, thereby minimizing light loss while achieving contrast enhancement.
Solution Approach 2:
A light-absorbing layer is introduced as an intermediary element between the reflective material and the external environment. This intermediate layer selectively absorbs stray light in critical regions without affecting the reflective properties of the underlying coating, thus improving contrast while preserving light extraction efficiency.
3Ease of manufacture
If phosphor sidewalls are exposed during bead blast processing or cleaning, then manufacturing is simplified, but contrast reducing stray light is generated
Solution Approach 1:
The patent applies protective or functional coatings to the phosphor sidewalls before final processing steps. This preliminary action ensures that even if sidewalls are exposed during manufacturing, they already have surface properties that minimize stray light generation, thus maintaining contrast without complicating the manufacturing process.
Solution Approach 2:
The surface properties of the phosphor sidewalls are modified through controlled changes in surface roughness, coating application, or material composition. These parameter changes reduce the stray light generating capability of the exposed sidewalls while maintaining manufacturing simplicity, achieving a balance between ease of fabrication and optical performance.
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 effectively absorbs stray light, reduces glare, and significantly improves the near-field contrast of the LED package, ensuring better performance in applications with optics.
Implementation Method 1
reflective materials can be used to reflect side emitted light back into the phosphor
Implementation Method 2
a light absorbing layer is positioned on the light reflective material to at least partially surround the phosphor and define a gap therebetween... absorbs light guided through bulk of the reflective side coat
Data Source
Figure 1~2B
Figure 3A~3B
Figure 4A~4B
AI summary
A method is described for providing an LED package including a LED stack having an LED, a phosphor layer, and a sacrificial layer, the LED stack having a top and a sidewall. The top and sidewall of the LED stack are covered with a light reflective material, followed by removal of any excess light reflective material from the top of the LED stack. Using screen printing or other suitable techniques, a light absorbing layer is deposited on the light reflective material, with the deposited light absorbing layer at least partially surrounding the LED stack and defining a gap therebetween of at least 30 microns.