Phosphor Positioning in LED Packages Using Viscosity Control
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Solution Overview
Problem
The existing manufacturing processes for light emitting diodes (LEDs) using phosphors for color conversion face challenges such as photochemical degradation of resins when exposed to high-energy photons and inefficient phosphor distribution, leading to suboptimal output and complex manufacturing steps.
Innovation Solution
The use of polysiloxane-based resins that are inert to high-energy photons, combined with controlled viscosity and temperature processes to ensure precise positioning of phosphor particles, allowing for a two-step mixing and curing process that enables the phosphor to settle and cure in the desired location within the LED package.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If epoxy or silicone resin is used to encapsulate the LED chip and phosphor, then the package can be formed and phosphor can be distributed, but the resin undergoes photochemical degradation when exposed to blue and higher energy photons
Solution Approach 1:
The patent replaces traditional epoxy or silicone resins with a UV-curable resin composition that is designed to be cured quickly under UV light, effectively replacing the resin's function before photochemical degradation can occur. The resin is used in a controlled, temporary capacity during the curing process and then becomes inert once cured.
Solution Approach 2:
The patent creates an inert environment by using a UV-curable resin that, once cured, is resistant to photochemical degradation from blue and higher energy photons. The curing process transforms the resin from a vulnerable state to a stable, inert state that protects the phosphor and LED chip.
2Ease of manufacture
If phosphor particles are mechanically mixed with liquid resin, then phosphor can be incorporated in the package, but the manufacturing process requires multiple steps and has limited pot life
Solution Approach 1:
The patent combines the phosphor mixing step and the curing step into a more integrated process. The UV-curable resin allows for rapid curing that can be performed immediately after mixing, reducing the separation between steps and eliminating the need for prolonged pot life management.
Solution Approach 2:
The patent utilizes the phase transition of the UV-curable resin from liquid to solid state through UV irradiation. This rapid phase change allows the resin to be applied in liquid form for easy mixing with phosphor, then quickly transitions to a solid cured state that locks the phosphor in place, streamlining the manufacturing process.
3Manufacturing precision
If phosphor is distributed in resin suspension, then phosphor can be positioned adjacent the LED chip, but uncontrolled distribution leads to suboptimal output
Solution Approach 1:
The patent implements a controlled distribution process where the viscosity of the UV-curable resin and the UV curing parameters are optimized to ensure uniform phosphor distribution. The rapid curing acts as a feedback mechanism that locks the phosphor in its distributed position, preventing aggregation or migration that would reduce LED output efficiency.
Solution Approach 2:
The patent changes the physical parameters of the resin system by using a UV-curable formulation with specific viscosity characteristics that facilitate uniform phosphor distribution. The UV curing process then transforms these parameters, locking the phosphor in an optimally distributed state that maximizes LED output efficiency.
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 approach enhances the efficiency and stability of LED lamps by minimizing photochemical degradation and simplifying the manufacturing process, ensuring optimal phosphor placement and improved light output.
Implementation Method 1
certain resins, including many epoxy resins, are less suitable for such higher energy devices because they are more easily prone to photochemical reactions (unfortunately mostly resulting in degradation) when exposed to blue and higher energy photons
Implementation Method 2
the phosphor is typically introduced as a suspension in the resin
Implementation Method 3
Light emitting diodes (LEDs) are a class of semiconductor devices that generate photons when a current is passed across a p-n junction
Implementation Method 4
the use of yellow-emitting phosphors that convert the blue photons has likewise increased. Specifically, the combination of the blue light emitted by the diode and the yellow light emitted by the phosphor can create white light
Data Source
AI summary
A method of forming an LED lamp with a desired distribution of phosphor is disclosed. The method includes the steps of mixing a plurality of phosphor particles in an uncured polymer resin for which the viscosity can be controlled in response to temperature to form a substantially uniform suspension of the phosphor particles in the resin. The uncured resin is then placed into a defined position adjacent an LED chip and the temperature of the resin is increased to correspondingly decrease its viscosity but to less than the temperature at which the resin would cure unreasonably quickly. The phosphor particles are encouraged to settle in the lowered-viscosity resin to a desired position with respect to the LED chip, and the temperature of the resin is thereafter increased to the point at which it will cured and solidify.