Why are silicones used in LED and Lighting applications?

Silicones have become widely used by LED design engineers to provide improved light performance, environmental protection and extended product life.  

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Applications

Automotive vehicle lighting

Signage and displays for sports and advertising

Back lighting for LCD screens

Screens and displays in vehicles

Aviation display lighting & airport lighting

Stage & theatre lighting

Rail & road signalling systems

Architectural & street lighting

Domestic lighting

Industrial machine lighting

Medical

 

Features

Thermal properties for efficient heat transfer

Environmental protection

High refractive index

Non-yellowing catalyst systems

Low viscosity to flow around complex parts

Self-bonding grades

Flame retardant, UL listed silicones

 

Heat Resistant Silicone Rubber for LED Lighting

Silicone solutions for LED lighting systems

Today&#;s elastomer market presents an extensive range of rubbers available to lighting engineers, designers and buyers. With so much choice on offer, it is imperative to select the correct specification of rubber with suitable grades, forms and thickness to ensure application performance.

Silicone rubber, with its superb sealing properties, ability to withstand high temperatures and lightweight features makes it the material of choice for both indoor and outdoor LED lighting applications.

Selecting the right material for LED lighting applications is crucial, as significant downtime and repair costs can occur if electrical enclosures fail to keep out water, moisture or dust ingress. Our material engineering specialists have developed a high-performance closed cell silicone sponge which boasts many protective properties including heat and weathering resistance.

Optically Clear Silicone

Not all lighting solutions are created equal, that is why at SMI we focus on the custom solution that our lighting manufacturer partners need. We offer micromolding and overmolding for tight tolerances and compression molding. Additionally, part of SMI custom solutions is our ability to adhere silicone to other parts or materials including bonding to plastic, metal, or other silicone parts.

Some of the most common lighting applications featuring silicone include: lenses for emergency vehicles, lighting in surgical settings, close contact lighting, alternatives to plastic light enclosures, applications requiring high heat, and other critical applications that cannot allow for broken bulbs.

LED encapsulation

 

LED (light-emitting diode) has the characteristics of energy saving and environmental protection, long life, low use voltage, short switching time, etc., and is widely used in lighting, display, backlight and many other fields. At present, it is developing in the mature technology direction of higher brightness, high color, high weather resistance, and high luminous uniformity.

 

Why LED packaging is important?

The LED industry chain can be divided into upstream, middle, and downstream, which are LED chips, LED packaging and LED lighting applications. As an LED package that connects the upper and lower levels in the LED industry chain, it plays an important role in the entire industry chain.

 

LED is composed of the led chip, bonding wire, led bracket, conductive adhesives, packaging materials, etc., among which packaging materials are one of the key factors affecting LED performance and service life.

 

Why use silicone material for LED encapsulation?

At present, due to its special requirements for light transmission, the main materials currently used on the market are epoxy resin, silicone, polycarbonate, glass, polymethacrylate and other high-transparency materials. However, since most of these materials are hardened and inconvenient to process, they are basically used for outer lens materials.

 

Traditional LED epoxy resin encapsulation materials have defects such as large internal stress, poor heat resistance, and easy aging, which cannot meet the increasingly developing needs of LED packaging materials, and are gradually being replaced by silicone materials or silicone-modified materials.

 

Silicone materials are low-stress materials with high UV resistance and aging resistance, making them ideal for LED encapsulation materials. The light transmittance of silicone resin is proportional to the luminous intensity and efficiency of LED devices, and the higher the light transmittance, it is conducive to increasing the luminous intensity and efficiency of LED devices. Since gallium nitride chips have a high refractive index (about 2.2), the refractive index of general silicone materials is only 1.4, so improving the refractive index of silicone materials can reduce the difference with the refractive index of the chip, reduce the light loss caused by interface reflection and refraction, and enhance the light efficiency of LED devices.

 

Modified epoxy resin for LED packaging

Epoxy resin has a high refractive index and light transmission, and the mechanical and adhesive properties are quite good, so there are still some products in the market. By introducing silicone functional groups to modify epoxy resins, the high-temperature performance and impact resistance of epoxy resins can be improved, the shrinkage and thermal expansion of products can be reduced, and the application range of products can be improved, even in the harsh environments. According to the reaction mechanism, silicone-modified epoxy resins can be divided into two methods: physical blending and chemical copolymerization.

 

The chemical copolymerization method uses the active groups on the silicone polymer, such as hydroxyl and alkoxy groups, to react with the epoxy groups on the epoxy resin to produce a copolymer for the purpose of modification. As early as , this method was used to carry out research on the use of silicone copolymer-modified epoxy encapsulation materials for LED products, and their experiments proved that this encapsulation process method could significantly improve the impact resistance and high and low-temperature resistance of the encapsulation materials, and significantly reduce the shrinkage and thermal expansion coefficient.

 

Silicone epoxy resin has recently been more widely used as it can reflect the advantages of both epoxy resin and silicone resin. It has shown excellent performance in mechanical properties, bonding, aging resistance, UV resistance, refractive index, light output, etc. It is a future research direction for LED packaging materials and will definitely make significant progress.

 

Silicone resin for led encapsulation

 

1 Characteristic of silicone materials

Silicone polymers have Si&#;O bonds as the main chain, and organic groups are connected to the silicon atoms, for example, R3 SiO1 /2( M) &#;R3 SiO2 /2( D) &#;R3 SiO3 /2( T) &#;R3 SiO2( Q) and other chain links are combined in a certain proportion; the Si-O bond energy is high, which makes it have better high-temperature resistance or radiation performance, and the Si-O bond angle is large, which can make the molecular chain of the material soft. Silicone materials have excellent properties in terms of heat resistance and anti-yellowing, so as to can be used in outdoor environments. Silicone materials are easy to modify, and functional groups with improved refractive index, such as sulfur, benzene, phenol, and epoxy groups, can be introduced into the side chain to improve the refractive index of packaging materials and improve the luminous efficiency of the LED device.

 

2 Synthesis of silicone resin

According to its refractive index, it can be divided into two types: low refractive index (1.4) and high refractive index (1.5). Since the higher the refractive index of the silicone material, the higher the light extraction efficiency, so the refractive index of the silicone material should be increased as much as possible.

 

Silicone resins are generally prepared from organosilanes by hydrolysis and polycondensation in the presence of solvents. The raw material for synthesis is generally chlorosilane or alkoxysilane. The specific process is as follows: firstly, silane is hydrolyzed into silanol under certain conditions, secondly, silanol itself undergoes a polycondensation reaction, and thirdly, it is neutralized by water washing and concentrated to remove small molecules to obtain silicone resin.

 

Silicone Rubber Encapsulation Materials

Silicone LED encapsulation materials can also be made from molded liquid silicone rubber. Liquid silicone rubber encapsulation material is made of vinyl-containing linear polysiloxane as the base polymer, vinyl silicone resin as reinforcing filler, and hydrogen-containing silicone oil as cross-linking agent. The molding silicone rubber does not produce by-products in the vulcanization process, has a very small shrinkage rate, and also has high cross-linking density, which is widely used in many fields. The use of molded silicone polymers as packaging materials for white LED devices has the effect of reducing costs and improving the service life of LEDs. Low-viscosity liquid silicone rubber has excellent penetration.
 

GaN-based power type white LED is the focus of current development. It has the characteristics of high heat, short light wavelength, etc., and has stricter requirements on the performance of packaging materials. At the same time, the use of packaging materials with high refractive index, UV resistance, heat aging and low stress can significantly improve the light output power of LED, and can also extend the pot life of the product. At the same time, the development of high-power LED devices also requires silicone packaging materials to develop products with high transparency, refractive index, UV aging and heat aging resistance as early as possible. In view of the problems of silicone materials, such as low refractive index, poor adhesion and low mechanical strength, the epoxy modification method is used to combine the advantages of the two or hybrid with inorganic materials to improve the refractive index of silicone materials.

 

With rich experience and considerate service, we are recognized as a reliable supplier of Functional Coatings Paints Manufacturer,Synthetic Polymers Resins For Wide Industry Supplier,optical encapsulants for led,silicone materials for leds,High Refractive Index Encapsulation Materials For Led,Csp Encapsulation Silicone,Functional Coatings Manufacturer,Barrier Coatings For Food Packaging,Sustainable Tableware Coating Supplier,Metal Packaging Coatings Manufacturer

At present, the commonly used encapsulation materials for LED electronic components mainly include epoxy resin, silicone, and other materials with high transparency. Epoxy resin has become the mainstream material of low-power LED packaging because of its excellent bonding performance, electrical insulation, dielectric performance, low cost and easy molding. But for power LED and printed circuit boards, congenital defects such as strong moisture absorption, easy aging, poor heat resistance and impact resistance of epoxy resin directly affect the service life of LED, and the color change under high temperature and short wave light directly affects the luminous efficiency. It is far from meeting the requirements of packaging materials in terms of high refractive index, low stress and high temperature aging resistance, so it is not suitable for power LED packaging materials.

 

High-performance silicone potting compounds and encapsulation materials have a series of excellent properties, such as high light transmittance, low internal stress, excellent high and low-temperature resistance, moisture insulation, UV and ozone aging resistance, good hydrophobicity and electrical insulation, and have widely become an ideal choice for LED potting and encapsulation applications materials.

 

Performance requirements of LED

encapsulation

 materials

Different encapsulation forms require different materials. In recent years, LED has been developing in the direction of high power, high energy efficiency, high brightness and high reliability. This puts forward higher requirements for the optical properties, mechanical properties, aging resistance and construction properties of silicone potting and encapsulation materials. Good optical properties can ensure that LED light can be output more effectively, and good mechanical and adhesive properties can make LED chip-sensitive components better protected. Good aging resistance can prolong the service life of LED, and good construction performance can improve encapsulation compound efficiency.

Characteristics of silicone materials

Silicone materials are a kind of polymers with Si-O-Si bond as the main chain and side chains connected with various organic groups through silicon atoms.

 

Silicone materials have the dual characteristics of both organic polymers and inorganic materials, with high bond energy (452KJ/mol), large bond length (0.165nm), bond angle (109) of Si-O bond, low rotational hindrance of Si-O bond and good flexibility of chain segment, good thermal conductivity.

 

These inherent properties make silicone rubber materials have a series of excellent chemical resistance properties for protecting electrical components: excellent high and low-temperature resistance, which can work in the temperature range of-50 &#;-250 &#;; excellent aging resistance (heat resistance, ultraviolet resistance, ozone aging resistance), with several decades of service life in the natural environment; good hydrophobicity, surface energy as low as 21-22mN/m2; high light transmittance and very low internal stress; excellent electrical insulation for radiator leak sealing applications, good flexibility for vibration isolation applications, etc.

What is the classification of silicone encapsulant

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aterials

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Silicone encapsulant materials can be divided into two categories: low refractive coefficient and high refractive coefficient according to their use. in some special applications, there will be medium refractive coefficient products between them.

 

The refractive index of encapsulation materials with low refractive coefficient is 1.40 ~ 1.45, most of them are silicone methyl encapsulant materials, and the refractive index of high refractive coefficient silicone packaging materials is 1.50 ~ 1.55, most of which are phenyl silicone packaging materials.

 

However, due to the large difference between the refractive index of the silicone packaging adhesive with a low refractive coefficient and the refractive index of the chip, part of the light is fully reflected back into the chip, affecting the light output.

 

At present, the preparation of phenyl-containing vinyl polysiloxane and hydrogen-containing polysiloxane to obtain high refractive index encapsulation materials is one of the more mature and widely used methods. Silicone high refractive encapsulation materials generally use a two-component addition vulcanization system.

What is the curing principle of silicone encapsulant

Generally, the curing principle of silicone encapsulant material is to use vinyl silicone resin or silicone oil as the base glue, Si-H containing silane oligomer as the crosslinking agent, and platinum complex as the catalyst to form the encapsulant elastomer resists weathering, high or low temperatures, thermal shock and so on. The addition crosslinking room temperature curing reaction occurs between Si-CH=CH2 and Si-H of silicone polymer under the action of the catalyst.

Addition reaction equation

What is the composition of silicone encapsulant

Silicone potting and encapsulation raw materials are two-component colorless and transparent liquid substances. Component a generally includes base glue, catalyst and tackifier, and component B generally includes base glue, crosslinking agent and inhibitor. A small amount of reinforcing filler and pigment can be added according to the use situation.

1. Base glue

It is mainly an R-vinyl silicone resin / R-vinyl silicone oil, which provides vinyl groups that can participate in the reaction. R groups can be methyl, phenyl, tetrachlorophenyl and aminopropyl, etc., which are endowed with different packaging characteristics by connecting different groups.

 

Common synthesis methods mainly include functional siloxane hydrolysis condensation method, cyclosiloxane anionic ring-opening polymerization method, siloxane catalytic equilibrium method, etc. vinyl silicone oil or silicone resin can also be prepared by cationic polymerization with acid catalysts such as trifluoromethane sulfonic acid and cation exchange resin.

2. Crosslinker

It is generally a low-viscosity hydrogen-containing silicone oil (such as XJY-702 Methylhydrosiloxane, Dimethylsiloxane Copolymer series) or silicone resin (such as XJY- vinyl MQ silicone resin), by controlling the molecular weight of hydrogen-containing silicone oil and functional group distribution and active hydrogen content and distribution, which can improve the performance of silicone encapsulation materials. The commonly used synthesis methods of hydrogen-containing silicone oil are generally hydrolysis condensation or cationic ring-opening polymerization under acidic conditions.

3. Catalyst

In this type of reaction, the catalyst is mainly used to catalyze the addition reaction of vinyl and active hydrogen to fast curing, and complexes such as platinum and palladium are generally used as catalysts. Among them, platinum-based catalysts with higher catalytic efficiency have a high catalytic effect at a concentration of 10-100 ppm.

 

However, silicone materials for LED encapsulation have high requirements for transparency and catalytic activity. At present, there are kinds of literature showing that the Karstedt catalyst and Speier catalyst are due to the use of tetramethyltetravinylcyclotetrasiloxane, tetramethyldivinyl Ethyl disiloxane, methyl vinyl phenyl cyclopolysiloxane or isopropanol solution are used as coordination solvents, which increase the compatibility with silicone resins and improve the overall performance, and have become the current silicone packaging materials. The most commonly used synthesis catalyst.

4. Inhibitors

Although the amount used in the reaction system is very small, it plays a crucial role in improving the storage stability of the reaction system, inhibiting the hydrosilylation reaction, and preventing excessive crosslinking. Commonly used inhibitors include ethynyl cyclohexanol, triphenyl propargyl alcohol, heavy metal ion compounds, 6-12-membered cyclic siloxane oligomers containing olefin groups, and benzotriazoles.

Ethynyl cyclohexanol

Triphenyl propargyl alcohol

5. Tackifier

Because there are no reactive groups on the surface of the substrate, ordinary addition-type silicone materials have little adhesion to the substrate. In order to maintain good sealing between the packaging material and the LED device, the packaging material must have good adhesion to the LED bracket and the bottom plate material. A common solution is to introduce tackifiers into LED packaging materials. Commonly used tackifiers include silane coupling agents and silane coupling agents modified (containing epoxy, acryloxy and vinyl) polysiloxanes. A large number of experiments have confirmed that the silicone tackifier modified by the silane coupling agent can greatly improve the bonding and sealing performance with the substrate without affecting its transparency and mechanical properties.

Polysiloxane tackifier modified by silane coupling agent

6. Reinforcing fillers

There are mechanical property issues with traditional two-component addition silicone materials, thus it requires reinforcing filler to meet the mechanical properties of packaging materials.

 

Commonly used reinforcing fillers mainly include fumed silica and MQ silicone resin, etc. For the special requirements of LED packaging materials for transparency, currently, the most commonly used silicone packaging material reinforcement filler is MQ silicone resin with good compatibility with the system. MQ silicone resin is a kind of silicone resin containing both monofunctional Si-O chain unit (M) and tetrafunctional Si-O chain unit (Q). MQ silicone resins such as vinyl MQ silicone resin and hydrogen-containing MQ silicone resin have good compatibility with the silicone packaging material system for LEDs and the reinforcement effect is obvious.

 

With the continuous improvement of power and brightness and the rapid development of white LEDs, silicone encapsulation materials have advantageous over EP encapsulation materials. Among them, high-refractive-index silicone packaging materials will be ideal matrix resin for high-power LED packaging. With the continuous breakthrough of technical barriers, the application scope of high-refractive-index silicone packaging materials will continue to expand, and many domestic LED lighting manufacturers will promote and apply it.

XJY Silicones&#;First choice silicone raw material supplier of potting compounds

 and encapsulation materials

XJY Silicones, one of China's leading silicone MQ resin manufacturers, has 30+ years of R&D and manufacturing experience and 15+ related patents in the silicone industry, also can customize the products according to your potting and encapsulating applications requirements. 

Methyl Vinyl VMQ silicone

Cross-linking agent: Hydrogen-containing silicone oil

 

Contact us to discuss your requirements of Molding Silicone For High Output Leds. Our experienced sales team can help you identify the options that best suit your needs.