Silver Alloy Reflective Coating for LED Corrosion Resistance
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Solution Overview
Problem
Light emitting diodes (LEDs) face issues with environmental degradation, corrosion, and tarnishing of pure silver reflective coatings, which affect their reflectivity and adhesion, leading to reduced light output and lifespan over time, especially in applications requiring consistent light emission over extended periods.
Innovation Solution
A reflective coating composed of a silver bismuth composition with 0.4% bismuth and a silver tin copper samarium composition with 0.5% tin, 0.2% copper, and 0.2% samarium is applied to the rear surface of LEDs, providing improved corrosion resistance, adhesion, and stability, preventing sideways infiltration and maintaining high reflectivity through the manufacturing process, including sputtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If pure silver reflective coating is used on LED rear surface, then high reflectivity is achieved, but environmental degradation and corrosion occur leading to reduced reliability
Solution Approach 1:
The patent applies composite materials by combining silver with small amounts of other metals (bismuth, tin, copper, samarium) to create alloy coatings that maintain high reflectivity while improving corrosion resistance. Specifically, silver-bismuth alloys with 0.01-5% bismuth and silver-tin-copper-samarium alloys with specified compositional ranges are used to create reflective coatings that resist environmental degradation better than pure silver while preserving optical properties.
Solution Approach 2:
The patent changes the compositional parameters of the reflective coating by introducing controlled amounts of alloying elements. The silver-bismuth coating uses 0.01-5% bismuth content, while the silver-tin-copper-samarium coating uses 0.1-5% tin, 0.01-1% copper, and 0.01-1% samarium. These parameter changes transform the coating from pure silver to engineered alloys with enhanced reliability.
2Illumination intensity
If pure silver reflective coating is used on LED rear surface, then high reflectivity is achieved, but adhesion properties deteriorate over time
Solution Approach 1:
The alloy coatings combine silver with other metals to create composite structures that inherently improve adhesion. The silver-bismuth and silver-tin-copper-samarium alloys create more stable bonding interfaces with the LED substrate and encapsulant materials, preventing delamination and maintaining strong adhesion throughout the product lifecycle while preserving high reflectivity.
Solution Approach 2:
Instead of attempting to improve adhesion of pure silver through additional layers or treatments, the patent inverts the approach by modifying the silver itself through alloying. The adhesive properties are built into the coating material composition rather than being added as separate functional layers.
3Reliability
If alloy compositions are used instead of pure silver, then corrosion resistance improves, but manufacturing complexity increases
Solution Approach 1:
The patent defines specific compositional parameter ranges for the alloy coatings: silver-bismuth with 0.01-5% bismuth, and silver-tin-copper-samarium with 0.1-5% tin, 0.01-1% copper, and 0.01-1% samarium. These standardized parameter ranges simplify manufacturing by providing clear specification targets while achieving the desired corrosion resistance improvement.
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 ensures high light emission and reflectivity for long periods, resisting corrosion and thermal cycles, thereby extending the life of LEDs and preventing degradation of light output.
Implementation Method 1
A light emitting diode is provided having a light emitting front surface and a rear surface with a reflective layer on the rear surface
Implementation Method 2
The coating can be applied to the light emitting diode by sputtering
Data Source
AI summary
A light emitting diode with a front surface adapted to emit light and a rear surface is provided with a reflective coating on the rear surface, the reflective coating being primarily silver and containing either 0.4% bismuth or a combination of 0.5% tin, 0.2% copper, and 0.2% samarium.