Unpackaged LED lamps with secondary optical design

The novel unpackaged LED has better heat dissipation conditions and integrates epitaxy, die and packaging processes, making it easier to match secondary optical design lighting fixtures…

　　LED light source applications will gradually shift to LED general lighting applications after the peak of LCD backlight application demand. However, unlike LCD backlight module design, LCD backlight modules do not need to consider light type and lighting application conditions, and are mainly based on the luminous efficiency requirements of the unit module; but LED lighting applications, in addition to brightness requirements, must also consider light type, heat dissipation, whether it is conducive to secondary optical design, and matching lamp design configuration requirements, etc., which actually places higher requirements on LED light source components.

　　Early packaging technology limitations and heat dissipation issues affect the development of high brightness design

　　In the early days of LED light source components, the packaging materials mainly used cannonball-shaped packaging bodies, which were quite common in the early days of high-luminous-efficiency blue light LEDs. As the demand for thinner designs of smartphones and mobile phones has been driven, the demand for surface-mount devices (SMD) LED light sources has gradually increased. LED light source components designed with surface-mount technology can use tape-and-reel material feeding to accelerate production and processing efficiency. In addition to increasing processing efficiency through automated production, it also brings new application markets for LED packaging technology. With the subsequent advancement of epitaxial structure and packaging technology, the luminous efficiency of LED light source materials has gradually surpassed the performance of traditional lamps.

　　Observing the needs of lighting applications, the requirements for luminous efficiency of lighting fixtures are getting higher and higher. The technical key to the light output efficiency of LED light sources is that the luminous efficiency is mainly affected by epitaxy, grains and packaging technology solutions. At present, the unit luminous efficiency of epitaxy has reached its limit, and the space for further leaps in luminous efficiency is relatively limited. Continuously increasing the grain area and improving packaging technology are relatively feasible solutions that can significantly increase the luminous efficiency of unit components. However, if the cost performance of components is to be further improved, there is no room for cost optimization by increasing the grain area. Instead, the choice of packaging technology will directly affect the cost of terminal material components. In other words, packaging technology will become the key to the cost of lighting LEDs.

　　Wafer-level packaging introduces LEDs with small size and high reliability

　　Chip Scale Package (CSP) is the most popular packaging technology solution in the LED industry in 2013. In fact, CSP is not a new technology in the semiconductor industry, but it is still a new and advanced technology in the application of LED light source components. The purpose of traditional semiconductor chip-level packaging is to reduce the final volume of the component after packaging, while improving heat dissipation and enhancing the application reliability and stability of the chip itself. The chip-level packaging of LED light-emitting components is mainly defined as the package body is close to the LED chip or the package body volume is not more than 20% of the chip, and the LED itself must be a fully functional packaged component after chip-level packaging.

　　Wafer-level packaging is mainly used to improve the increasing number of logic chip pins, enhance component heat dissipation performance and miniaturize chips. Through the integration benefits of wafer-level packaging, the parasitic phenomena of chip components can be reduced, while the component integration of Level 2 packaging can be increased. The application of wafer-level packaging in LED light source devices can also achieve significant benefits.

　　Typical chip-level packaging does not require additional secondary substrates, lead frames, etc., but can directly attach the chip to the carrier. Chip-level packaging is to make the P/N electrodes of the LED diode at the bottom of the chip, and can use surface mounting automation to assemble components. Compared with the production process that requires wire bonding to make components, chip-level packaging can relatively improve the assembly and testing process, while achieving the dual goals of reducing processing complexity and cost.

　　LED adopts chip-level packaging solution, which can provide better heat dissipation performance, high lumen output, high packaging density, more flexibility, simplified substrate and other advantages. At the same time, the lack of wire bonding process can also improve the reliability of terminal components.　Unpackaged LED solutions are popular for high luminous angle and luminous efficiency .

　　The pursuit of high brightness performance, low cost and more convenient production conditions has also promoted the use of novel unpackaged LEDs (Embedded LED Chips). Comparing the characteristics of unpackaged LEDs and chip-level packaged LED components, unpackaged LEDs have better heat dissipation performance. Unpackaged LED manufacturing technology integrates epitaxy, grain and packaging processes, and components can also be integrated with secondary optical design, which can also make the terminal product have higher brightness, larger luminous angle and smaller volume. At the same time, it can achieve the purpose of reducing production costs. Light-emitting components can provide lighting manufacturers with diversified and more flexible design space.

　　In the traditional packaging structure, the reflector cup forms an internal cavity, and the chip bonding process is used to process the driving power series connection. Although the process is simple, it also limits the heat dissipation capacity of the terminal components. In the new LCD backlight and lighting fixture design requirements, LED light source components must reduce the light-emitting area while increasing the driving wattage of the unit component. The key to heat dissipation has become a technical bottleneck for such application requirements.

　　Unpackaged LEDs can reduce component thermal resistance by about 10 times compared to traditional packages. Unpackaged LEDs do not require a reflector cup cavity, which can save the cost of making the reflector cup and optimize the cost-performance of the overall component. This is also the technical advantage of unpackaged LEDs. Unpackaged LEDs are bonded with special fluorescent films to further increase the LED's luminous angle to 160 degrees, effectively improving the component's luminous efficiency, structural characteristics, and heat dissipation advantages.

　　Unpackaged LED technology has a very small luminous area and a large luminous angle. Compared with the performance of light source components of traditional packaging solutions, the light type of unpackaged LED technology is closer to a point light source. This material property makes unpackaged LED technology more suitable for secondary optical processing design. The smaller luminous area also means that the volume of the component is relatively smaller. It can also be used with thinner optical lenses to make LED light source modules. It can be especially applied to the use needs of some lighting products with limited space in some structures, such as LCD direct backlight or flat panel lighting products.

　　Compared with chip-level packaging, the unpackaged LED technology introduces the lamination process of fluorescent adhesive film in the manufacturing process, which can make it easier to control the luminous performance characteristics in LED light source lighting applications, so that the lamps and lanterns are also equipped with luminous color detection and matching procedures in the production process, greatly simplifying production.

　　Improved thermal conduction structure, better thermal resistance performance of non-packaged LED

　　In traditional LED packaging, the chip must be processed through a sapphire substrate and insulating glue to conduct heat to the chip. In contrast, in the unpackaged LED technology, in order to utilize the flip-chip chip structure and the metal substrate eutectic manufacturing technology concept, the thermal resistance of the component itself can be lower due to the design structure of the flip-chip and the metal substrate eutectic in the package of the unpackaged LED component. Therefore, under the same driving wattage, the core temperature of the chip's light-emitting area can be effectively reduced in the unpackaged LED technology, and at the same time, it can also reduce the problem of component failure or shortened life caused by the continuous high temperature of the chip.

　　However, unpackaged LEDs are not perfect process technologies, because to achieve the purpose of unpackaged LED design, it is necessary to integrate epitaxy, die, packaging processes and surface mounting technologies of finished components. The technical difficulty of integration is quite high, especially in the critical flip chip structure design. It is actually quite difficult for unpackaged LEDs to maintain high reliability performance of components. It is mainly necessary to seek diode materials with high reflectivity, high thermal conductivity and good adhesion. At the same time, these materials must have high stability characteristics and must be able to withstand the high temperature, high pressure and high current environmental conditions when the components are operating.

　　In addition, unpackaged LEDs have no outer packaging body for protection. If the lighting equipment needs to be placed in a harsh environment with high temperature and high humidity, a protective layer must also be designed for the components to increase the service life of the light source device.

　　In addition, in the unpackaged LED process, fluorescent film is used to replace traditional packaging materials during the packaging process, and fluorescent powder is also placed inside the fluorescent film to match the LED light source and the fluorescent powder to produce white light. The choice of fluorescent powder will affect the reliability, luminous efficiency, and high-temperature performance of unpackaged LED components in lighting applications.

　　After all, fluorescent film is different from traditional packaging materials. It needs to deal with bonding and testing issues during the manufacturing process. Not only are there differences in production equipment, but related process equipment also needs to be optimized and improved, which will increase the complexity of the initial production of unpackaged LED components.

　　Although packaging LED lamps can improve the heat dissipation problem of LED lamps, it is not perfect. Without packaging, more integration technology is needed, which is quite difficult. High difficulty will inevitably involve cost issues. Whether it can dominate depends on the maturity of the technology.