A ) LED packaging materials with performance requirements
LED packaging materials used one hand to meet the requirements of the packaging process , on the other hand to meet the requirements of LED work . Currently , epoxy potting material in the domestic market accounts for a large proportion , the resin itself has excellent electrical insulation, adhesion, dielectric properties , transparency, and good adhesion ; same storage stable formulations and flexible operation simple, but higher operating temperatures and ultraviolet radiation transparent epoxy resin to make a serious decline , it is difficult to meet the requirements of high-power led street light wholesale package , many experts even believe that packaging materials and processes behind the development of the LED industry has played a bottleneck effect.
Packaging material requirements for the performance of the process
In order to meet the needs of the operation process of the actual LED assembly , packaging materials should have a suitable viscosity, adhesion and temperature resistance , including: ( 1 ) physical properties of the cured before the general characteristics after curing . The physical properties of the cured before associated with interoperability , wherein the viscosity and curing properties is particularly important. Due to the high impact polymer material expansion after thermal curing , produce significant shrinkage of the material cools , resulting in the interface with the surrounding material of the stress , sparking peeling phenomenon of the material cracks , so the low-temperature curing as possible. ( 2 ) surface adhesion. The exposed surface of the package having an adhesive sealing material , bonded to each other causes the sealing material between this selection can not be peeled off from the machine condition causes reduced operability . Further, in use, the stick will produce dust, reduce the brightness of the case . From the peeling resistance , in terms of crack resistance , require more flexible packaging material , but in general, the higher the viscosity of a soft material , therefore , a need for a good balance between these two a material . ( 3 ) Lead-free reflux . Lead solder surface treatment requirements in recent years, more and more, it also shows that the heat resistance of the packaging materials have become increasingly demanding . Counter at a high temperature , the result will produce coloring caused dramatic changes in the thermal peeling , cracks , wire breakage .
Light transmittance
LED packaging materials for absorbing visible light causes the decrease in light extraction efficiency , the encapsulating material has a low extinction ratio for high transparency. Relatively epoxy resins , silicone resins transparency even better. Ultraviolet transmittance silicone resin encapsulation material can reach more than 95% , so that the light transmittance and luminous intensity LED devices has been greatly improved.
Index of refraction
The difference in refractive index between the LED chip and the package material in light extraction efficiency will have a great impact , thereby increasing the refractive index of the material, make it as close as possible the refractive index of the LED chip , through the beneficial light. In general, the refractive index of the LED chip ( / 7 = 2.2-2.4 ) is much higher than the refractive index of silicone encapsulating material ( / 7 = 1.41 ) , when the chip emitting passes packaging materials, will occur at the interface reflection effect, causing most of the light is reflected back inside the chip , can not effectively export, brightness performance direct damage. To solve this problem, you must increase the refractive index of packaging materials to reduce reflection losses. Studies have shown that , with the increase of the refractive index of the package , the LED brightness can be obtained increases, the red LED device , when the refractive index of the encapsulating material is 1.7 , the external light extraction efficiency of 44% can improve . Therefore, the development of high refractive index transparent material to reduce the difference between the refractive index of chip and package materials , and its importance is obvious.
Heat aging resistance and light aging
In the high-power high -brightness LED , the encapsulating material will not only be very strong light, heat is also affected by the chip , and therefore , packaging materials need to have light resistance and heat resistance. Even prolonged exposure to high temperatures , sealing materials are also required to ensure no discoloration , stable physical properties.
Status ( two ) power LED packaging materials research
Silicone / epoxy encapsulation material
With LED power and brightness increases, epoxy light, heat aging and other aspects have been difficult to meet the packaging requirements. However, epoxy resins have excellent dielectric , adhesive properties , especially cheap, low cost. So over a period of time, researchers did not abandon the use of epoxy resin , but take advantage of silicone modified epoxy way to develop both the advantages of the two materials of the packaging materials .
Considering the LED chip emitting heat aging is mainly caused by the encapsulating material , some manufacturers in the package sheet adjacent the brush inner silicone material , an epoxy resin and the outer lens material selection , PC, PMMA and the like. However, practical application discovery , epoxy , PC, PMMA and aging resistance is not enough, and the inner silicone material exists and poor interfacial compatibility .
When silicone-modified epoxy resin for packaging materials used , the material toughness and resistance to high temperature has obviously improved. Has been reported to the mixture and molding the silicone resin ring vanadium mixed with the epoxy resin as a sealing material containing a vinyl group and si 0H group and the polyorganosiloxane base polymer as a specific structure , a crosslinking agent , catalysts, diluents , dubbed packaging materials for LED packaging , heat test does not change color after a 40-120 oC thermal shock no peeling and cracking occurs, high luminous efficiency LED . There is also a modified epoxy siloxane ring polyorganosiloxane mixture encapsulated material vanadium compound is reported ] , a mixture of epoxy-modified polyorganosiloxane with an aliphatic or alicyclic epoxy compounds , Dong agent with an acid for thirty the packaging material has a uV light aging resistance , thermal shock resistance , high transparency, and high hardness and good adhesion to the substrate , fraud is very suitable wavelength below 500 nm emission peak of the blue , and white LED package. A specific structure and an epoxy polyorganosiloxane dubbed I, ED epoxy encapsulation material can improve heat resistance, aging resistance uV light , but also to improve the adhesion of the silicone material , sticky surface attached , and is a noteworthy development approach .
Japan Shin-Etsu Silicone hydroxyl using silicon resin, a silicone oil, silicone rubber and the epoxy resin mixture of a silicon hydride with anti heart finally obtained after molding of 70 (Shore D), 1.51 (nd, 25 ℃) modified resin material , thermal shock resistant to nearly a thousand times the number of experiments.
U.S. patent GE reported the first hydrolytic polycondensation of the silane to give a silicone resin containing hydroxyl groups , and then with the silicone resin, silicone -modified epoxy compound , the preparation of high temperature curing molding material up to 1.60 refractive index . The material (5mm thickness ) by the light radiated wavelength 380nm or 500 h at 150 ℃ by UV irradiation wavelength of 400-450 nm after 500 h , still higher than 80% transmittance .
Quartz powder , silicon , aluminum , zinc , glass fiber material used to improve the heat resistance of the LED package and heat conductivity . Reported in U.S. Patent nanoscale spherical glass powder and nano-scale silica added to the silicone-modified epoxy resin , the refractive index of the encapsulating material prepared up 1.56 , the transmittance exceeds 95 % by the thermal shock of 200 failure rate does not exceed 15 %.
Silicone packaging materials
Although a large number of studies have reported proved silicone modified epoxy resin material can improve performance, but the molecular structure of silicone-modified materials containing epoxy, material adverse radiation resistance , and there is easy yellowing problem. Optical clarity and thermal stability of silicone materials play an important role in the high brightness and high reliability LED applications. Silicone materials are rapidly replacing epoxy and other organic materials , providing a wide range of potting materials for a variety of LED applications, lens materials, adhesives , sealants and protective coating products.
Currently silicone sealant on the market is divided into two types: type and ordinary refractive index of the high refractive index silicone materials, including gels, silicone rubber and silicone . Ordinary refractive index of the silicone is polydimethylsiloxane -based, high refractive led street light wholesale phenylmethyl silicone based Dun alkyl cyanide . Three international companies Dow Corning Silicone , Momentive , Shin-Etsu Silicones products with high refractive index based packaging materials in the domestic high-end market position of absolute dominance .
Currently on the market several mainstream silicone LED packaging materials suppliers is Shin-Etsu , Dow Corning , Momentive and Nusil technology , they have launched a refractive index of more than 1.50 of silicone and silicone products. Which Dow Corning high polymer technology research company has 120 years of history , the study of LED packaging materials at the advanced level , product range, market prices from 5000 to 6000 kg , the major brands have a high refractive index products : SR7010, OE26336, OE6550 , JCR6175 etc. Shin-Etsu 's excellent anti-aging product performance, positioning the higher market price of 7,000 yuan / kg, the main brands are : SCR-1012, KER-2500, LPS-5547 and so on. Momentive silicone outstanding operability , the market price of 5,000 yuan / kg , the flagship IVS products, brands have 5332,5862,4542,4622 and so on.
In order to improve the refractive index of the encapsulating material with a high refractive index can study said phenyl-containing silicone oil, and the link of hydrogen with a platinum catalyst for the curing reaction of the base polymer , only the refractive index of the material can be significantly improved, and mechanical strength, thermal properties of light have different degrees of improvement . Can also improve the quality of the fraction of the sealing material to reduce shrinkage phenyl such organic silicon material , improve its resistance to thermal shock cycle resistance, excellent mechanical properties and adhesive properties. Furthermore, it was the added liquid silicone rubber molding by injection molding , the experiment proved that you can reduce shrinkage of the rubber material . For the resin material , the same applies to the injection molding has been reported that the preparation of the same rigid material , injection molding can make the elastic modulus increased by about 3% , without affecting the light-transmitting material , and inorganic filler can also be effectively improve the heat resistance of silicone rubber and radiation resistance . Recently it has been a long cycle for the packaging material is cured , the curing temperature is higher about the research , a photosensitive agent is added to the formulation , irradiation with visible light or UV -curable , only 15-20 min to cure completely , while other properties are not affected . Silicone LED encapsulation materials are typically a platinum catalyst , a platinum catalyst and the short retention time , is prone to yellowing of the light transmissive sealing material adverse properties , for someone using the silicone -containing ligands do phenylethenyl , study difficult to change a platinum catalyst , the catalyst was prepared using a high silicon rubber sealing material refractive index of the light transmitting properties of more than 95 %.
From the current market, silicone molding packaging materials plus the amount of phenyl silicone resin encapsulation material significantly increasing trend , silicone easy processing , high refractive index , light transmission properties and good adhesion properties , and resistance to UV light and thermal aging ability, increase the amount of the two segments of functionality to some extent can also improve its impact resistance , can be used for LED packaging , or the lens material. In addition to using the UV -curable silicone resin , the excellent properties can be obtained packaging materials, especially prominent anti- tarnish material , power type can be used to package a white LED.
In summary prepared by foreign high refractive index silicone LED packaging material is easy to see that they were in the choice of selecting a base polymer containing phenyl polysiloxane . Currently containing phenyl polysiloxane prepared only for the production of its low-end product performance is not required , and high performance with phenyl polysiloxane is still dependent on imports. It is because of this reason , the current reports about domestic high refractive index silicone materials is not much , but it has gradually made some progress .
Institute of Chemistry in the laboratory has prepared a refractive index of 1.56 silicone oil ; Hangzhou Normal use of hybrid siloxane ring ring-opening polymerization reaction in toluene solvent , 4O ~ 80 ℃ cation exchange resin catalyst , preparation hydrogen-containing end groups to obtain a colorless and transparent silicone oil , a refractive index of 1.39 ~ 1.51 (25 ℃). Institute of Chemistry has developed a silicone- modified epoxy LED lens material , but the material is resistant to ultraviolet light , heat aging performance than silicone . Recently, Shenzhen Optoelectronic Technology Co., Ltd. reported Guoke composite silicone and silicone oil mix , be prepared using Hydrosilylation packaging material transmittance up to 98 % in the high-power white LED on the application and achieved good results .
Conclusion
With further study of the luminous efficiency of LED devices , packaging materials for the light aging, thermal aging , refractive index, and put forward a new light-transmitting requirement . The current domestic LED packaging companies have started using and heat aging properties of transparent silicone material with excellent resistance to UV light instead of epoxy as a packaging material , such material has become several large foreign companies and research institutions of research and product development hotspot.
No doubt , silicone encapsulating material is ideal for LED package to meet the requirements , are rapidly replacing epoxy and other organic materials , providing a wide range of potting materials for a variety of LED applications, lens materials, adhesives , sealants and protective coating products. However, with the rapid development of LED industry , the need for brightness , use, packaging process and design diversification produced a different hardness, refractive index greater demand for packaging materials , and in order to ensure the reliability of packaged , select the appropriate hardness and adhesion of the material is also very important. Currently LED package silicone material has the following main problems : ( a ) the chemical structure and the organosilicon composition perspective, a high refractive index is more difficult to use high refractive index ultrafine nanoparticles will change l Health concern. ( 2 ) the thermal conductivity of the silicone material is low, to increase the thermal conductivity of aluminum it is necessary to increase the filling rate , high conductivity silver auxiliary materials . However , the prior art only in transparency can not be obtained , the need for further technological breakthroughs. ( 3 ) Compared to other LED packaging materials , silicone although there are many advantages, but it does not itself possess strong mechanical strength , high thermal expansion , to compensate for this deficiency, the material needs to be modified . The above points on the silicone industry will be very tough challenges.
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