LED encapsulant is a general term for organic silica materials in the LED optoelectronic industry. Because the anti-ozone ability of epoxy is weak, the colloid turns yellow, affecting the light transmission effect, and the silica gel material has excellent performance against atmospheric aging and ultraviolet aging. In the high-end product application, the epoxy resin has been used by the LED silica material. replace. Well-known brands at home and abroad include: HISUNS in the UK, HITACHEM in Japan, Dow Corning, Shinetsu, GETOSHIBA, Taiwan's Tianbao and so on.
classification:
1. According to the type of molecular chain group: it can be divided into methyl organic silica gel and phenyl organic silica gel. At present, most of the LED optoelectronics market is widely used in methyl organic silica gel. Phenyl organosilicone is used only in demanding fields due to its high cost.
2, according to the field of use: can be divided into
LED lamp bead packaging with organic silica gel and LED application products potting with silica gel. The organic silica gel for LED lamp bead packaging includes lens-filled silica gel and LED solid crystal silica gel. The price of silicone for LED application products is relatively low, as long as it is used for waterproofing, such as LED water low-light encapsulation silica gel, solar LED lamp sealing silica gel,
LED display protects silicone, LED module transparent silicone and so on.
3, according to the vulcanization conditions: can be divided into high temperature vulcanized LED silica gel and room temperature vulcanized LED silica gel. Regardless of the type of silica gel, no exotherm occurs during vulcanization. High-temperature vulcanized silica gel is a high molecular weight polysiloxane (molecular weight is generally 400,000 to 800,000). Room temperature vulcanized silicone rubber generally has a low molecular weight (3 to 60,000), and is provided at both ends of the molecular chain (sometimes in the middle). One or two functional groups, under certain conditions (moisture in the air or a suitable catalyst), these functional groups can react to form a high molecular weight crosslinked structure. Room temperature vulcanized silicone rubber can be divided into condensation type and addition molding according to its vulcanization mechanism; it can be divided into two types of two components and one component according to its packaging method.
Performance characteristics: The basic structural unit of the LED silica gel product is composed of silicon-oxygen chain links, and the side chains are connected to various other organic groups through silicon atoms. Therefore, in the structure of
high-power LED silica gel products, it contains both "organic group" and "inorganic structure". This special composition and molecular structure make it combine the properties of organic matter with the function of inorganic substances. One body. Compared with other polymer materials, the most outstanding performance of LED silicone products is:
1. Temperature resistance
The LED silica gel product is based on a silicon-oxygen (Si-O) bond. The bond energy of the CC bond is 82.6 kcal/g molecule, and the bond energy of the Si-O bond is 121 kcal/g in the LED silica gel. Molecule, so LED silica gel products have high thermal stability, and the chemical bonds of molecules at high temperatures (or radiation) do not break or decompose. High-power LED silicone is not only resistant to high temperatures, but also low temperature resistant and can be used over a wide temperature range. Whether it is chemical or physical and mechanical properties, it varies little with temperature.
2. Weather resistance
The main chain of LED silica gel products is -Si-O-, which has no double bonds and is therefore not easily decomposed by ultraviolet light and ozone. High-power LED silica gel has better thermal stability and resistance to radiation and weathering than other polymer materials. LED silica gel has a service life of up to several decades in the natural environment.
3. Electrical insulation performance
LED silicone products have good electrical insulation properties, and their dielectric loss, withstand voltage, arc resistance, corona resistance, volume resistivity and surface resistivity are among the best in insulating materials, and their electrical properties are affected by temperature and frequency. The impact is small. Therefore, they are a stable electrical insulating material and are widely used in the electronics and electrical industries. In addition to excellent heat resistance, LED silica gel also has excellent water repellency, which is a guarantee for high reliability of electrical equipment under wet conditions.
4. Physiologically inert silicone compounds are one of the most inactive compounds known. They are very resistant to biological aging, have no rejection reaction with animals, and have good anticoagulant properties.
5. Low surface tension and low surface energy High power LED silica gel has a very sturdy main chain, and its intermolecular force is much weaker than that of hydrocarbons. Therefore, it has lower viscosity and weaker surface tension than hydrocarbons of the same molecular weight. The surface energy is small and the film forming ability is strong. This low surface tension and low surface energy are the main reasons for its multi-faceted application: hydrophobic, defoaming, foam stabilization, anti-sticking, lubrication, glazing and other excellent properties.
1. Application on LED lamp beads:
On the high-power LED and SMD LED lamp beads, the fixing of the chip, the mixing of the phosphor of the white LED lamp bead, and the filling of the lens type are all performed by the LED silica gel.
(1) LED silica gel for solid crystal: The chip is commonly called solid crystal glue, which is often mixed with silver powder to improve the heat conduction effect, so it is called solid crystal silver glue on the market.
(2) LED mixed phosphor silica gel: white LED is uniformly covered by a layer of ** fluorescent light on the surface of the blue
LED chip , and the blue light passes through the phosphor to achieve white light effect, which requires the use of LED mixed phosphor silica gel.
(3) Surface-filled LED silica gel: The surface of the LED lamp is used to protect the LED chip. Commonly used are high-power LED lens filling, lens molding, chip-type planar packaging,
COB -type large-area non-standard packaging, etc. .
2. Application on LED application products:
LED applications are very broad, and life lighting, traffic warning, aerospace technology, underground operations, etc. have been widely used. The purpose of LED silicone used in LED applications is to waterproof to protect the internal circuitry of the product. Commonly used are black potting silicone for LED display PCB protection, sealed potting silicone for LED lamps, etc.
The main problems in high power LED package adhesive applications:
Regarding the silica gel for high-power LED packaging, I believe that all of you have encountered many questions in the process of using it. The explanation given by the supplier is also varied. Let me use LED to do some personal observation. I hope that everyone will come together to discuss and promote common development.
All of the following explores me only for silicone, eliminating all the accessories on the LED.
The production of LED silica gel is simply composed of three materials: resin, active body and initiator. I can say for sure that in Dow Corning, Toshiba, Shin-Etsu, these three products will not contain any non- Substance in silicon. However, among the customers in our mainland, the products that you really use are not necessarily the same. I believe that you all know that the price of such products is basically maintained at around RMB6000, which has prompted many manufacturers to make some changes:
First, adding epoxy resin, a little bit of common knowledge of glue knows that after adding epoxy in silica gel: the adhesion to PPA will increase, it will have no effect on your curing, the hardness when doing MOD can also meet the requirements, even say Light transmission refraction will have no effect.
But it will cause yellowing of the rubber layer, which is why many people who do white light react to discoloration (of course, it causes white light discoloration and because you use phenyl silicone, we use silica gel to be divided into methyl The simplest difference between the class and the phenyl group is that it has better weather resistance with the methyl group, while the phenyl group has a better refractive index)
Adding an epoxy can easily cause a dead light because the shrinkage of the epoxy and the silicone during curing is inconsistent, which leads to the detachment of the leads on the chip.
Therefore, I hope that everyone must be careful when choosing glue.
Second, add phosphors, if you have a little understanding of silica gel, you know how difficult it is to achieve 75HA hardness, of course, here is not silicone, and many of our domestic counterparts have thought of a way to pass Add some filler to achieve the required hardness, but there will be two shortcomings at this time. First, the viscosity of the product will increase, which is not conducive to our actual operation, and the yellow layer of the rubber layer will be cured after curing. In order to control the yellowing of the color, the addition of phosphors, the use of neutralization between the light, so that everyone can not detect, but such a trick can not stand the test of time, up to six months or more, all the stuffing The next two points are a lot of domestically produced silica gel and earning profits by changing the imported rubber. At the same time, the above two points are also for silica gel of methyl type, such as DC-6301 and KER-2500, which are well-known. At the same time, the phenyl glue, such as DC6550, etc., they add most of the high-refraction liquid to them, and at the same time, the refractive index is guaranteed at the same time. This is something that a friend can't ignore in the pursuit of refractive index.
Various problems encountered in the use of silica gel:
First, the surface wrinkles after curing. This is caused by shrinkage, and most of the time it is caused by the addition of solvent-based silicone resin to the glue. It is recommended that you change the glue.
Second, the interface layer appears. This problem is also caused by glue. There is an interface between any two different materials. The only way to solve it is to use the principle of similar materials. Many friends have proposed to increase the curing temperature or to perform sintering at high temperatures. These are some of the words that can be solved. The only solution that can be solved is to start with the material and change the affinity of the silicone when it cannot change another material.
Third, the phosphor is precipitated, and the problem of powder is eliminated. The glue in this case can only be cured at room temperature, because in order to maintain its light transmittance, refractive index, etc. in the silica gel, no suspending agent can be added. Going in, friends who encounter these problems can try to change to a warming and curing product, which can solve this problem.
Fourth, the surface is not smooth enough after curing. This is because the glue is caused by poisoning such as S and P. Everyone cleans the mold and other tools.
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