Abstract

Lens arrays are introduced to diminish the total internal reflection (TIR) that happens at chip-encapsulant and encapsulant-air interfaces of chip-on-board light-emitting diodes (COB-LEDs), so as to improve the light extraction efficiency (LEE) of the COB-LEDs. However, the LEE of COB-LEDs with lens array depends on the refractive index of the encapsulant layer ${n_{{\rm encap}}}$ and lens array ${n_{{\rm lens}}}$, which was rarely concerned so far. Optical simulations based on a Monte Carlo ray tracing method, and experiments were conducted to investigate the effect of ${n_{{\rm encap}}}$ and ${n_{{\rm lens}}}$ on the LEE of COB-LEDs with millilens array. The simulated results show that the TIR at chip-encapsulant, encapsulant-lens, and lens-air interfaces can be significantly diminished by regulating the ${n_{{\rm encap}}}$ and ${n_{{\rm lens}}}$, and the LEE of COB-LEDs decreases as the refractive difference of encapsulant layer and lens array $|{n_{{\rm lens} -}}{n_{{\rm encap}}}|$ increases. Compared to the COB-LEDs with only a flat encapsulant layer, the LEEs of blue and white COB-LEDs with ${n_{{\rm lens}}} = {n_{{\rm encap}}} = {n_{{\rm ITO}}} = {2}$ are enhanced by 246.2% and 50.6%, where ${n_{{\rm ITO}}}$ is the refractive index of the top layer of the conventional LED chip. The experimental results agree well with the simulated results with normalized LEE deviation within 7.3%.

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© Optical Society of America

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Are you interested in learning more about Low Refractive Index Silicone For Cob Led Encapsulation? Contact us today to secure an expert consultation!

Optically Clear Materials

Liquid resins are used in two main ways in encapsulations processes. The first methods is glob top and dam & fill alternatively known as frame & fill. The second method is Casting and Potting that can be used to encapsulate sensitive electronics as well as opto-electronic devices. In the case of LEDs they can be both cast or potted.

When an LED is cast, liquid resin is poured into the LED chamber and cured into the shape of the cavity. This produces a stand-alone device which can then become a component in another printed circuit board assembly. In the potting process, LEDs are already wired and connected to a circuit board or substrate. The circuit board or substrate usually already has a frame or cavity which is then filled with a liquid resin and then cured. This results in a group of LEDs set in a ready-to-go circuit board or substrate.

Casting and Potting can be used to encapsulate sensitive electronics as well as opto-electronic devices. In the case of LEDs they can be both cast or potted.

In the casting process, liquid resin is poured into the LED chamber and cured into the shape of the cavity. This produces a stand-alone device which can then become a component in another printed circuit board assembly.

In the potting process, LEDs are already wired and connected to a circuit board or substrate. The circuit board or substrate usually already has a frame or cavity which is then filled with a liquid resin and then cured. This results in a group of LEDs set in a ready-to-go circuit board or substrate.

CAPLINQ offers a range of Encapsulants, Potting Materials and Casting Materials

CAPLINQ OPTOLINQ™ OLS-Series are a family of optically clear (often called “water-white”) liquid encapsulants that are used to encapsulate optical or optoelectronic devices that require both a high level of light transmittance as well as a good level of mechanical protection. Products in this OLS-Series family can be epoxies, silicones or hybrid technologies. They are used extensively for the encapsulation of LED devices but could be well suited for other applications that require a clear, optical grade encapsulation system.

There are three main types of liquid resin for potting and casting applications: Epoxy, Polyurethane, and Silicone.

Resin encapsulants are used to protect and insulate electronic components from harsh environments, including moisture, thermal shock, physical vibration and shock, chemicals and dust, etc, which help electronics achieve stable performance in long term. Potting resin encapsulants are widely applied due to their usage flexibility and easy automation.

In order to meet different application needs, the properties of resin encapsulants could be adjusted. There are mainly three types of resin chemistry systems being widely applied as liquid encapsulants. The comparison between the key performance considerations is shown in the table below. Some other considerations are not mentioned here, such as flame retardancy, volatility, dielectric resistance, etc.

Hardness It is a key consideration for selecting materials. Depending on your applications and purpose of encapsulating, you need different levels of hardness. Hard materials provide better mechanical protection against the environment. Soft materials absorb vibrations well and make the component easy to repair and rework.

Thermal Conductivity The components being encapsulated may generate different levels of heat in the area, especially high power electronics. Potting materials could help to dissipate heat to ensure long-term reliability of electronics. The thermal conductive value could be adjusted by adding various fillers.

Color & Viscosity Depending on the visibility requirement of your application, you may need transparent, dark opaque, or even specific colors; Generally speaking, potting materials are designed to have low viscosity (<10 Pa.s) to ensure flowability and self-leveling for easy usage. Medium and high viscosity (>100 Pa.s) products are suitable for sealing and adhesion.

Curing Process Besides the above-mentioned properties, you may consider the curing conditions like temperature and time which suit your production and also the components. Pot life and application process also.

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