Reflective Solder Mask for LED Phosphor Package
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Solution Overview
Problem
Existing packaging techniques for phosphor-converted LEDs result in significant light absorption by the substrate and submount, reducing the overall efficiency of the module.
Innovation Solution
A reflective solder mask made of highly reflective materials like TiO2 or ZnO is applied over the substrate, with a reflective ring surrounding the LED dies to redirect downward light, and a phosphor is deposited within the ring to encapsulate the LEDs and enhance light extraction, while minimizing submount size to reduce light interception.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional substrate is used to mount LED dies, then the substrate provides mechanical support and heat sinking, but the substrate absorbs significant downward light reducing module efficiency
Solution Approach 1:
The patent converts the substrate from a light-absorbing harmful element into a light-reflecting beneficial element by coating it with a highly reflective solder mask material. This reflective coating redirects downward light back through the phosphor layer, transforming the substrate's previously harmful light absorption into a useful light extraction mechanism that increases overall module efficiency.
Solution Approach 2:
The patent applies different properties to different parts of the substrate by using a selective solder mask pattern. The solder mask is applied only in specific regions where light reflection is beneficial, while leaving other areas open for electrical connections and heat management. This localized application optimizes light extraction without compromising the substrate's mechanical and thermal functions.
2Ease of operation
If submounts are used to support LED dies, then handling and soldering are simplified, but the submount surface intercepts and absorbs downward light
Solution Approach 1:
The patent applies the same reflective solder mask coating to the submount surface, converting it from a light-absorbing element into a light-reflecting element. This maintains the submount's mechanical support and handling advantages while eliminating its harmful light absorption, allowing downward light to be redirected back through the phosphor layer for improved light extraction.
Solution Approach 2:
The solder mask is selectively applied to the submount surface in regions where light reflection is beneficial, while leaving electrode areas and heat management regions exposed. This localized approach preserves the submount's electrical and thermal functions while adding light extraction enhancement where needed.
3Loss of energy
If a reflective solder mask is applied over the substrate, then light extraction efficiency is improved, but additional processing steps are required
Solution Approach 1:
The patent merges the reflective coating function with the existing solder mask application process. By using the same solder mask material to provide both electrical insulation and light reflection, the invention combines multiple functions into a single processing step, avoiding the need for separate reflective coating operations and eliminating additional process complexity.
Solution Approach 2:
The solder mask material is selected to serve multiple functions simultaneously: electrical insulation, mechanical protection, and light reflection. This multi-functionality allows a single material layer to address multiple requirements, eliminating the need for separate functional layers and simplifying the overall device structure and manufacturing process.
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 significantly improves light extraction efficiency by reflecting downward light and converting it into usable white light, achieving an improvement of greater than 10% in overall module efficiency without adding additional processing steps.
Implementation Method 1
The dielectric is a highly reflective material, such as a binder including TiO2, ZiO2, VO2, or other suitable reflective particles, that scatter and reflect any impinging light
Implementation Method 2
The dielectric is a highly reflective material, such as a binder including TiO2, ZiO2, VO2, or other suitable reflective particles, that scatter and reflect any impinging light
Implementation Method 3
The combination of the blue light leaking though the phosphor and the yellow-green phosphor light creates white light
Implementation Method 4
a starting substrate comprises aluminum for sinking heat
Data Source
AI summary
A mounting substrate has a patterned metal layer defining a plurality of top metal bond pads for bonding to bottom metal bond pads of LED dies. A solder mask layer is formed over the mounting substrate, where the mask has openings that expose the top metal bond pads and protects metal traces on the substrate. The mask layer is a highly reflective white paint. The exposed top metal bond pads are then wetted with solder. The LED dies' bottom metal bond pads are then soldered to the exposed top metal bond pads, such that the mask layer surrounds each LED die to reflect light. A reflective ring is affixed to the substrate to surround the LED dies. A viscous phosphor material then partially fills the ring and is cured. All downward light by the LED dies and phosphor is reflected upward by the ring and solder mask layer.