Light emitting diodes are light emitting dies that get their color or hue through the phosphor that is coated on top of the die. They are typically blue tinted and are getting their color from a combination of the phosphor, the die light intensity and the overmolded optoelectronic molding compound. There are multiple LED types for a huge variety of applications, ranging from simple through hole monochrome LEDs to backlight, organic, miniLEDs and industrial baylights. All of these LED types have the same principle but completely different application and reliability requirements.

Light emitting diodes generate light upon the absorption of electrical energy. include a multitude of technologies and devices that utilize the interaction between light and materials. To maximize light generation and emission, LEDs are designed to minimize reflection at material interfaces and are encapsulated with materials that allow light transmission while protecting the LED.

Target Applications for Next-Generation LED Materials

• UV LEDs for applications below 300 nm, where transmission is challenging

• Mid- to high-power LEDs with junction temperatures exceeding 150 °C, requiring UV-resistant materials due to epoxy and silicone degradation.

• Outdoor RGB SMD LED applications that require UV resist

• UV and  visible light reflectors with excellent temperature resistance and color stability, particularly in white

How can a diode produce light?

Diodes produce light through a process called electroluminescence. When an electron in a diode moves from a higher energy state to a lower one, it releases energy in the form of a photon. This energy can be visible as light if the diode is made of a material that allows for the emission of photons within the visible spectrum.

As discussed in diode application, free electrons can fall into empty holes from the P-type layer. This transition from a higher energy level to a lower one results in the emission of a photon. However, the specific frequency and energy of the emitted photon depend on the material used in the diode.

Standard silicon diodes, for instance, emit photons in the infrared range. This means the light they produce is invisible to the human eye. However, other materials, like gallium arsenide phosphide, can be used to create diodes that emit photons in the visible spectrum, producing visible light. These diodes are commonly used in LEDs (Light-Emitting Diodes) for various applications, including lighting, displays, and communications.

The main semiconductor materials used to manufacture LEDs are:

• Indium gallium nitride (InGaN): blue, green and ultraviolet high-brightness LEDs
• Aluminum gallium indium phosphide (AlGaInP): yellow, orange and red high-brightness LEDs
• Aluminum gallium arsenide (AlGaAs): red and infrared LEDs
• Gallium phosphide (GaP): yellow and green LEDs

How white light is produced?

There are several methods of generating white light using LEDs. Below is 2 typical emission methods.

Blue LED＋Yellow Phosphor

Combining a blue LED with yellow phosphor is a widely used method to produce white light. The blue LED emits light in the blue spectrum that passes through a layer of yellow phosphor, which is a material that absorbs some of the blue light and re-emits it as yellow light. The combination of the remaining blue light and the newly emitted yellow light creates white light. This is because blue and yellow are complementary colors, and when mixed, they produce a broad spectrum of light that appears white to the human eye.This method is easier than other solutions and provides high efficiency, making it the most popular choice on the market. 

Red LED＋Green LED＋Blue LED

Combining red, green, and blue LEDs can produce white light through a process called additive color mixing. When the light from these three primary colors is combined in the right proportions, it creates the perception of white light. This method is commonly used in full-color LED devices, such as screens and displays, to produce a wide range of colors by varying the intensity of each LED

General Considerations For LED Encapsulants

As LED encaplants, besides general consideration of packaging materials, optical performance with long-term reliability is specially emphasized. 

Challenges & Solutions

LED Clear Molding Compounds Product Overview 

Die Attach For LEDs

LOCTITE ABLESTIK ABP 8037TI silver-filled die attach adhesive paste is specifically designed to attach small diodes in high volume manufacturing. Even more specifically, it is the highest volume silver-filled die attach paste for high reliability LED attach and manufacture when using small die on Au-finished leadframes. Used in high-volume manufacturing throughout China and Malaysia.

Also extremely popular:

LOCTITE ABLESTIK 84-1LMISR4 is a manufacturer's product of choice, can be used for LED applications and like most epoxies it is suitable for Copper substrates.

One alternative:

LOCTITE® ABLESTIK ABP 8035M is a non-conductive clear silicone designed for high brightness LED die attach applications.

Non conductive option:

LOCTITE ABLESTIK QMI536NB creates packages and devices that have high resistance to delamination and popcorning after multiple exposures to lead-free solder reflow temperatures. It has good optical performance with high transmittance, Optical Density and HRI and is  a great solution for ASIC attach and LED attach.

High Purity Alumina (HPA) For LEDs

HPA as LED Encapsulant

LED encapsulation protects and packages LED chips to enhance their performance and longevity. Common types include epoxy encapsulants, which are cost-effective and transparent but have limited thermal conductivity and may yellow over time; silicone encapsulants, known for their excellent thermal stability and UV resistance but at a higher cost and slightly reduced transparency; and ceramic, offering superior thermal conductivity and mechanical strength, ideal for high-performance LEDs.

HPA as Coatings for Phosphors in LEDs

Phosphor is a substance that emits light when exposed to radiation, often used in LEDs to convert blue or ultraviolet light into white or specific colors. In LED lighting, phosphors are typically applied to the LED chip to create the desired light spectrum, enabling color tuning and enhancing brightness. High purity alumina is often used to coat phosphor particles, enhancing their stability and protecting them from moisture and chemicals. Its thermal stability ensures phosphors can withstand high temperatures without degradation, while its refractive properties improve light dispersion, resulting in more uniform and consistent lighting.

The purity of alumina used in LED production should be 99.99% (equivalent to Grade 4N) or higher. This exceptionally high purity is important, as even trace impurities can greatly affect the performance and lifespan of LEDs.

HPA-SDF is an advanced 5N high-purity alumina engineered for sapphire production, featuring spherical morphology, high crystallinity, and a controlled specific surface area. These key properties enhance its performance in precision optical applications, making it an ideal material for mini-LED and micro-LED displays, where superior clarity, durability, and efficiency are essential.

HPA M Series (M1, M3, & M5) - The HPA M Series is a high-purity (5N) alumina with an irregular morphology, designed for high temperature applications. The series is differentiated by its D50 particle size value, offering customized solutions for various requirements. Its unique irregular morphology makes it particularly well-suited for phosphor coatings in LED applications, enhancing light conversion efficiency and overall performance.

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