Factors Affecting the Light Efficiency of LED Injection Molding Module Packages
Time:2017/06/28 Article Release:本站
Shenzhen Oulite Optoelectronics Co., Ltd.'s brand "Oulite" is a company dedicated to LED light box lighting, A high-tech enterprise engaged in the research, development, production, sales and service of sign lighting and decorative lighting products.
The company has been focusing on LED light box lighting, sign lighting and decorative lighting products research and development since its inception. The feasibility study of various lighting solutions, adhere to high standards and strict requirements, and strive to achieve the design of each product to reach the international first-class standard, and each product developed and produced strives to be safe, practical and flawless. It is our consistent pursuit to provide customers with more energy-saving, environmentally friendly and efficient LED light box lighting and sign lighting solutions.
The company has an experienced R&D and production management team. Always in accordance with the international first-class production management concept, strict requirements for product quality and various production management work, the company's products mostly use CREE, SAMSUNG, OSRAM and other world-class manufacturers of LED lamp beads, all products have passed CE safety certification and EU RoHS environmental protection certification, Some products have passed UL certification.
At present, the company's main products are three series of sign light source, light box light source and decorative lighting light source, among which sign lighting The injection molding module in the product is popular at home and abroad with its excellent appearance and quality, and is deeply loved by customers. The high-power backlight and high-power side light sources in the light box light source are becoming the best choice for replacing traditional fluorescent tubes and CCFLs with their high-efficiency energy-saving capabilities and high cost performance.
The company's products are mainly used in airports, subways, high-speed railways, bus stops, petroleum, finance, automobiles, clothing , catering, shopping malls, star hotels, home improvement and other industries light box lighting, logo lighting, reflective dark groove lighting, backlight decorative lighting.
Pioneering and innovating, people-oriented, sustainable management, honesty, SUNLITE people are willing to open up Mentality and pragmatic attitude will work with you for mutual benefit, win-win cooperation, and create a better era of green energy saving!
The company's investment in LED injection molding modules It is huge. Six injection molding machines are lined up to form the main process flow of LED injection molding modules. For LED injection molding modules, our company has its own set of core technologies, which is a strong guarantee for product quality.
Conventional LED injection molding modules are generally bracket type, encapsulated by epoxy resin, with low power and exquisite Small and can be applied to many fields. With the development of LED chip technology and packaging technology, in line with the demand for high luminous flux LED injection molding module products in the lighting field, power LED injection molding modules have gradually entered the market. This kind of power LED injection molding module generally places the light-emitting chip on the heat dissipation bracket, and is equipped with an optical lens to achieve a certain optical spatial distribution. The lens is filled with low-stress flexible silica gel.
Power LED injection moulding module should really enter the lighting field and realize the daily lighting of the home. There are still many problems, the most important of which is the luminous efficiency. At present, the highest lumen efficiency reported by power LED injection molding modules on the market is around 50lm/W, which is far from meeting the requirements of daily household lighting. In order to improve the luminous efficiency of the power LED injection molding module, on the one hand, the efficiency of the light-emitting chip needs to be improved; on the other hand, the packaging technology of the power LED injection molding module also needs to be further improved. To start with, improve the packaging and light extraction efficiency of products.
Packaging elements that affect light extraction efficiency
1. Thermal Technology
For a light-emitting diode composed of a PN junction, when the forward current flows from the PN junction, the PN junction There is heat loss, and this heat is radiated into the air through adhesives, potting materials, heat sinks, etc. In this process, each part of the material has a thermal resistance that prevents heat flow, that is, thermal resistance, and thermal resistance is determined by the device. Fixed value determined by size, structure and material. Let the thermal resistance of the light-emitting diode be Rth(℃/W) and the heat dissipation power be PD(W). At this time, the temperature rise of the PN junction caused by the heat loss of the current is:
T(℃)=Rth×PD.
PN junction temperature is:
TJ=TA+Rth×PD
Where TA is the ambient temperature. Since the rise of the junction temperature will reduce the probability of light-emitting recombination of the PN junction, the brightness of the light-emitting diode will decrease. At the same time, due to the increase in temperature rise caused by heat loss, the brightness of the light emitting diode will no longer continue to increase proportionally with the current, that is, it will show the phenomenon of thermal saturation. In addition, with the rise of junction temperature, the peak wavelength of light emission will also shift to the long-wave direction, about 0.2-0.3nm/℃. This is for the white LED injection molding module obtained by coating the blue chip with YAG phosphor and mixing it. The drift of the blue light wavelength will cause a mismatch with the excitation wavelength of the phosphor, thereby reducing the overall luminous efficiency of the white LED injection molding module, and resulting in a change in the color temperature of the white light.
For power LEDs, the drive current is generally several hundred mA or more, and the PN junction The current density is very large, so the temperature rise of the PN junction is very obvious. For packaging and applications, how to reduce the thermal resistance of the product so that the heat generated by the PN junction can be dissipated as soon as possible can not only increase the saturation current of the product, improve the luminous efficiency of the product, but also improve the reliability and life of the product. . In order to reduce the thermal resistance of the product, the selection of packaging materials is particularly important, including heat sinks, adhesives, etc. The thermal resistance of each material should be low, that is, good thermal conductivity is required. Secondly, the structural design should be reasonable, the thermal conductivity of each material should be continuously matched, and the thermal conduction between the materials should be well connected, so as to avoid the heat dissipation bottleneck in the heat conduction channel and ensure that the heat is dissipated from the inside to the outside layer by layer. At the same time, it is necessary to ensure that the heat is dissipated in a timely manner according to the pre-designed heat dissipation channels.
2. Choice of filler
According to the law of refraction, when light is incident from an optically denser medium to an optically sparser medium, when the incident angle reaches a certain value, that is, greater than or equal to the critical angle, full emission occurs. For the GaN blue chip, the refractive index of the GaN material is 2.3. When the light is emitted from the inside of the crystal to the air, according to the law of refraction, the critical angle θ0=sin-1(n2/n1)
Where n2 is equal to 1, which is the refractive index of air, and n1 is the refractive index of GaN, thus calculating The critical angle θ0 is obtained to be approximately 25.8 degrees. In this case, the only light that can be emitted is the light within the solid angle of the incident angle ≤ 25.8 degrees. It is reported that the external quantum efficiency of the current GaN chip is about 30%-40%. Therefore, due to the internal absorption of the chip crystal , the proportion of light that can be emitted outside the crystal is very small. According to reports, the current external quantum efficiency of GaN chips is around 30%-40%. Similarly, the light emitted by the chip must be transmitted to the space through the packaging material, and the influence of the material on the light extraction efficiency must also be considered.
Therefore, in order to improve the light extraction efficiency of LED product packaging, the value of n2 must be increased, that is, to improve the packaging efficiency The refractive index of the material can be used to increase the critical angle of the product, thereby improving the encapsulation luminous efficiency of the product. At the same time, the encapsulation material absorbs less light. In order to increase the proportion of the outgoing light, the shape of the package is preferably domed or hemispherical, so that when the light is emitted from the packaging material to the air, it is almost perpendicular to the interface, so that total reflection is no longer generated.
3. Reflection processing
The reflection treatment mainly includes two aspects, one is the reflection treatment inside the chip, and the other is the light reflection of the packaging material Through internal and external reflection treatment, the proportion of luminous flux emitted from the inside of the chip is increased, the internal absorption of the chip is reduced, and the luminous efficiency of the power LED finished product is improved. In terms of packaging, the power LED injection molding module usually mounts the power chip on a metal bracket or substrate with a reflective cavity. The bracket-type reflective cavity generally adopts electroplating to improve the reflection effect, while the substrate-type reflective cavity generally The polishing method is used, and electroplating treatment is also performed if conditions permit. However, the above two treatment methods are affected by the precision of the mold and the process. The reflection cavity after treatment has a certain reflection effect, but it is not ideal. At present, the substrate-type reflective cavity made in China has poor reflection effect due to insufficient polishing accuracy or oxidation of the metal coating, which causes a lot of light to be absorbed after hitting the reflective area and cannot be reflected to the light-emitting surface as expected, resulting in the final result. The light extraction efficiency after encapsulation is low.
After various researches and experiments, we have developed an organic material coating with independent intellectual property rights. The reflection treatment process of the layer, through this process, makes the light reflected into the carrier cavity absorb little, and most of the light incident on it can be reflected to the light-emitting surface. The light extraction efficiency of the treated product can be increased by 30%-50% compared with that before the treatment. Our current 1W white light power LED's luminous efficacy can reach 40-50lm/W (tested on the remote PMS-50 spectral analysis and testing instrument), and a good packaging effect has been obtained.
4. Phosphor Selection and Coating
For white power LED injection molding modules, the improvement of luminous efficiency is also related to the choice of phosphors related to processing. In order to improve the efficiency of the phosphor to excite the blue chip, first of all, the selection of the phosphor should be appropriate, including excitation wavelength, particle size, excitation efficiency, etc., and needs to be comprehensively assessed, taking into account all performances. Secondly, the coating of phosphor powder should be uniform, preferably the thickness of the adhesive layer relative to each light-emitting surface of the light-emitting chip is uniform, so as to avoid partial light from being unable to be emitted due to uneven thickness, and at the same time, the quality of the light spot can be improved.
Good heat dissipation design plays a significant role in improving the luminous efficiency of power LED injection molding products. It is also a prerequisite to ensure product life and reliability. A well-designed light extraction channel, which focuses on the structural design, material selection and process treatment of the reflective cavity and filling glue, can effectively improve the light extraction efficiency of power LEDs. For power-type white LED injection molding modules, the selection of phosphors and process design are also crucial to the improvement of the light spot and the improvement of the luminous efficiency.
