Gum is A general term for organic silica materials in the photovoltaic 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.
First, the classification of LED packaging adhesive
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, Protect silica gel, LED module transparent silica gel, etc.
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.
Second, the problems often encountered in the use of silica gel
1. Surface wrinkling 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 to try the glue change.
2. Interface layer
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. When you can't change another material, change the affinity of silica gel. .
3. Phosphor precipitation
Exclusion is a problem of powder, and the glue in this case can only be cured at room temperature, because in order to maintain its light transmittance, refractive index, etc. in silica gel, it is impossible to add any suspending agent, and encounter these problems. A friend's door can try to replace it with a warming and curing product, which can solve this problem.
4. The surface is not smooth enough after curing
This is because the glue is caused by poisoning such as S and P, and it is necessary to clean the mold and other tools.
Third, the 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 groups" and "inorganic structures". This special composition and molecular structure make it combine the properties of organic matter with the function of inorganic substances. 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 C-C bond is 82.6 kcal/g molecule, and the bond energy of the Si-O bond is 121 in the LED silica gel. Thousands of calories per gram of molecules, so the thermal stability of LED silica gel products is high, 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. Physiological inertia
Polysiloxanes 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
The main chain of high-power LED silica gel is very compliant, and its intermolecular force is much weaker than that of hydrocarbons. Therefore, it is lower in viscosity than hydrocarbons of the same molecular weight, weak in surface tension, small in surface energy, and strong in film forming ability. . 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.
Fourth, the application
1. LED lamp beads application:
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 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.
Five, LED silicone selection considerations
1. Adding epoxy resin
Anyone who knows a little about glue knows that after adding epoxy to silica gel, the adhesion to PPA will increase, and it will have no effect on your curing. The hardness of MOD can also meet the requirements. Even the light-reflecting will not have any Impact.
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.
2. Add phosphor
If you have a little understanding of silica gel, you know how difficult it is to achieve 75HA hardness. Of course, it is not silicone, but many of our domestic counterparts have come up with a way to add some fillers. In order to achieve the required hardness, but this time there will be two shortcomings, one is that the viscosity of the product will increase, which is not conducive to our actual operation, and the yellow layer of the rubber layer after curing, in order to control the color of the hair Yellow, so adding phosphors, using the 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 stuff is exposed
The above two points are a lot of domestically produced silica gel and earn profits by changing the imported rubber. At the same time, these two points are also for methyl silicone, 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.
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