Introduction of high-power LED packaging glue

Reading Volume：【 1977 】

Time：【 2018-03-20 】

LED packaging glue is the general term for organic silicone materials in the LED optoelectronics industry. Due to the weak ozone resistance of epoxy, the colloid turns yellow and affects the light transmission effect. Silicone materials have excellent properties such as atmospheric aging and ultraviolet aging. In the application of high-end products, epoxy resin has been used by LED silicone materials. replace.
1. Classification of LED packaging glue
1. According to the types of molecular chain groups: it can be divided into methyl silicone and phenyl silicone. At present, most of the widely used LED optoelectronics market is methyl-based organic silica gel, and phenyl-based organic silica gel is only used in high-demand fields due to its high cost.
2. According to the field of use: it can be divided into organic silica gel for LED lamp bead packaging and silica gel for LED application product potting. The organic silica gel used for LED lamp bead encapsulation includes lens-filled silica gel and LED solid crystal silica gel. The price of silica gel for LED application products is relatively low, as long as it is used for waterproofing, such as LED water low light potting silica gel, solar LED lamp sealing silica gel, LED display protection silica gel, LED module transparent silica gel, etc.
3. According to vulcanization conditions: it 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 heat generation occurs during vulcanization. High-temperature vulcanized silica gel is a high-molecular-weight polysiloxane (molecular weight is generally 400-800,000), room temperature vulcanized silicone rubber generally has a low molecular weight (30,000-60,000), and it has 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 cross-linked structure.
Room temperature vulcanized silicone rubber can be divided into condensation type and addition molding according to its vulcanization mechanism; according to its packaging method, it can be divided into two types and single-component types.
2. Common problems encountered in the use of silica gel
1. Surface wrinkles after curing
This is caused by shrinkage. In most cases, it is caused by the addition of solvent-based silicone resin to the glue. It is recommended to change the glue and try.
2. Interface layer
This problem is also caused by the glue. There will be an interface between any two different materials. The only way to solve it is to use the principle of similar substances, and change the affinity of silica gel when another material cannot be changed. .
3. Phosphor precipitation occurs
Eliminate the problem of powder, then the glue in this case can only be room temperature curing type, because in order to maintain its light transmittance, refractive index, etc., any suspending agent cannot be added to the silica gel. Those who encounter these problems Friends can try to change to a product that is cured by heating to solve this problem.
4. The surface is not smooth enough after curing
This is because the glue is poisoned by S, P, etc., and a series of tools such as molds need to be cleaned.
Three, performance characteristics
The basic structural unit of LED silica gel products is composed of silicon-oxygen chain links, and the side chains are connected to various other organic groups through silicon atoms.
Therefore, the structure of high-power LED silica gel products contains both "organic groups" and "inorganic structures". This special composition and molecular structure make it integrate the characteristics of organic substances and the functions of inorganic substances. Compared with other polymer materials, the most outstanding properties of LED silicone products are:
1. Temperature resistance
LED silica gel products are based on the silicon-oxygen (Si-O) bond as the main chain structure. The bond energy of C-C bond is 82.6 kcal/mole. The bond energy of Si-O bond is 121 in LED silica gel. Kcal/mole, so LED silica gel products have high thermal stability, and the chemical bonds of molecules will not break or decompose under high temperature (or radiation exposure). High-power LED silica gel is not only resistant to high temperatures, but also resistant to low temperatures, and can be used in a wide temperature range. Whether it is chemical properties or physical mechanical properties, the change with temperature is very small.
2. Weather resistance
The main chain of LED silica gel products is -Si-O-, there is no double bond, so it is not easy to be decomposed by ultraviolet light and ozone. High-power LED silica gel has better thermal stability, radiation resistance and weather resistance than other polymer materials. The life span of LED silica gel in natural environment can reach several decades.
3. Electrical insulation performance
LED silica gel products have good electrical insulation properties. Its dielectric loss, voltage resistance, arc resistance, corona resistance, volume resistivity and surface resistivity are among the best insulating materials, and their electrical properties are affected by temperature and frequency. The impact is very small. Therefore, they are a kind of stable electrical insulating materials, which 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 used under wet conditions.
4. Physiological inertia
Polysiloxane compounds are among the most inactive compounds known. They are very resistant to biological aging, have no rejection reaction with animal bodies, and have good anticoagulant properties.
5. Low surface tension and low surface energy
The main chain of high-power LED silica gel is very flexible, and its intermolecular force is much weaker than that of hydrocarbons. Therefore, it has lower viscosity than hydrocarbons of the same molecular weight, weak surface tension, low surface energy, and strong film-forming ability. . This low surface tension and low surface energy are the main reasons for its many applications: hydrophobic, defoaming, foam stability, anti-sticking, lubrication, glazing and other excellent properties.
Four, application
1. Application on LED lamp beads:
On high-power LEDs and SMD LED lamp beads, the fixing of the chip, the mixing of phosphor powder on the white LED lamp beads, and the filling of the lens are all performed by LED silica gel.
(1) LED silica gel for solid crystal: chip fixing is commonly called solid crystal glue, and silver powder is often mixed to improve the thermal conductivity, so it is called solid crystal silver glue on the market.
(2) LED mixed phosphor silica gel: The white light LED is uniformly covered with a layer of fluorescent light on the surface of the blue LED chip. The blue light passes through the phosphor to achieve the white light effect, which requires the use of LED mixed phosphor silica gel.
(3) Surface filling of LED silica gel: The purpose of the surface silica gel on the LED lamp beads is to protect the LED chip. Commonly used are high-power LED lens filling, lens molding, SMD flat packaging, COB large area non-standard packaging, etc. .
2. Application on LED products:
The LED application field is very broad, and it has been widely used in life lighting, traffic warning, aerospace technology, and underground operations. The purpose of LED silica gel used in LED application products is to protect the internal circuit of the product. Commonly used are black potting silica gel for protection of LED display PCB boards, and sealing potting silica gel for LED lamps.
Five, the selection of LED silicone
1. Add epoxy
Anyone who has some common sense of glue knows that after adding epoxy to silica gel: the adhesion to PPA will increase, it will not affect your curing, and the hardness when doing MOD can also meet the requirements, even if there is no light transmission and refraction. Impact.
But it will cause the yellowing of the glue layer, which is why many friends who make white light react to discoloration (of course, it causes the discoloration of white light and it is also because you use phenyl silica gel. The silica gel we use is divided into methyl Among the two types and phenyl type, the simplest difference is that it has better weather resistance with methyl type, while phenyl type has better refractive index)
The addition of epoxy will easily cause dead lights. This is caused by the inconsistent shrinkage of epoxy and silicone during curing, which leads to the detachment of the leads on the chip.
So I hope everyone must be careful when choosing glue.
2. Add phosphor
If you have a little knowledge of silica gel, you know how difficult it is to achieve 75HA hardness. Of course, this is not silicone resin, but many of our domestic counterparts have thought of a way, by adding some fillers to it , So as to achieve the required hardness, but at 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. The other is that the glue layer has yellow edges after curing, in order to control the color development. Yellow, so the addition of phosphors and the neutralization of light make it impossible for everyone to detect it. However, such a trick cannot withstand the test of time. At most six months or more, everything is exposed.
The above two points are a lot of domestic silica gel and make profits by changing imported rubber. At the same time, these two points are also for methyl type silica gel, such as the familiar DC-6301, KER-2500 and other high-hard rubbers. At the same time, phenyl glues, such as DC6550, etc., they add most of the high-refractive liquid to it, which guarantees the refractive index while the cost is down. This is something that friends cannot ignore in the blind pursuit of refractive index.

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