The physical structure and technical principle of LED packaging

LED is a kind of can directly convert electrical energy into visible light emitting devices and radiation energy, has low working voltage, small power consumption, high luminous efficiency, light response time is very short, pure colors, firm structure, impact resistance, vibration resistance, stable and reliable performance, light weight and small volume. A series of characteristics of low cost, rapid development, high brightness, high performance products have been mass production of the visible spectrum section of various colors. Chinese red, green, orange, yellow LED accounted for about 12% of the total output of the world, "fifteen" during the industry goal is to reach an annual output of 30 billion capacity, the realization of LED wafer and chip high brightness AiGslnP production, with an annual output of more than 1 billion red, orange, yellow high brightness LED tube core key technical breakthrough of GaN materials, including blue, green and white LED in mass production. It is predicted that by 2005 the international market demand for LED is about 200 billion, sales of $80 billion. In the LED industry in the upstream link, LED substrate and substrate wafer production, the middle reaches of the industrialization of LED chip design and manufacturing, downstream to LED packaging and testing, packaging technology research and development of low thermal resistance, excellent optical properties, high reliable LED is a new type of industrialization, practical the only way which must be passed to the market, from a certain meaning is the link between the industry and the market, only a good package in order to become the end product, can be put into practical application, in order to provide service for the customer, make the industrial chain, seamless smooth. The particularity of LED packaging LED packaging technology is mostly based on the development and evolution of discrete device packaging technology, but there are a lot of special. In general, the core of the discrete device is sealed in the package, the main role of the package is to protect the core and complete the electrical interconnection. The LED package is complete the output signal, protection tube core work, output: the function of visible light, both electrical parameters, design and technical requirements and parameters of light, can not simply be discrete device packaging for LED. LED is the core of the P and N type semiconductor formed by the PN core, when injected into the PN junction of the minority carrier with the majority carrier compound, it will emit visible light, ultraviolet light or near infrared light. The emitted photons PN junction area is non directional, which is emitted in all directions have the same probability, therefore, not die for all light can be released, which mainly depends on the quality of semiconductor materials, the structure and geometry of the die package internal structure and encapsulation materials, application requirements to improve LED the internal and external quantum efficiency. Routine with 5mm type LED package is the side of 0.25mm square tube core bonding or sintering in the lead frame, die of positive spherical contact point and wire bonding is in the lead with a pin connected, negative reflection cup and another lead frame connected by pins, then top it with epoxy resin coating. The function of the reflecting cup is to collect the light emitted from the side of the tube core and the interface, and then transmit to the desired direction angle. At the top of the epoxy resin encapsulation is made into a certain shape, there are several functions: core tube protection from external erosion; using shape and different material properties (with or without adding color dispersing agent), lens or diffuse lens function, control the light divergence angle; tube core refractive index and refractive index of air is too large, resulting in the tube core internal total reflection critical angle is small, the active layer produced light is only a small part is most easily removed, many times in the reflection and absorption of inner core tube, prone to cause excessive loss of total reflection light, using epoxy resin the corresponding refractive index for the transition, improve the tube core the light emitting efficiency. The epoxy resin used as a shell must have the properties of moisture resistance, insulation, mechanical strength, high refractive index and high transmittance to the core. Selection of packaging materials with different refractive index, the influence of package geometry on the photon escape efficiency is different, the angular distribution of luminous intensity and die structure, light output, packaging material used and the shape of the lens. If the pointed resin lens can make light to the direction of the axis of LED, the corresponding angle is small; the top of the resin lens is round or flat type, the corresponding perspective will increase. Under normal circumstances, the wavelength of LED changes with the temperature of 0.2-0.3nm / C, the spectral width increases, affecting the color brightness. In addition, when the forward current flowing through the PN junction, the junction area of febrile loss temperature rise, near room temperature, temperature rise of 1 degrees Celsius, the intensity of LED will be reduced to about 1%, when the heat dissipation; keep the color purity and luminous intensity is very important, in the past using to reduce the drive current to the. Reduce the junction temperature, most of the LED drive current limit is about 20mA. However, the light output of LED will increase with the increase of current, at present, a lot of power LED driving current can reach 70mA, 100mA or even 1A level, need to improve the package structure, the new LED package design and packaging structure and technology of low thermal resistance, improved thermal characteristics. For example, the use of large area flip chip structure, the selection of a good thermal conductivity of silver glue, increase the surface area of the metal stent, solder bump of the silicon carrier directly installed in the heat sink and so on. In addition, in the application design, PCB circuit board, such as thermal design, thermal conductivity is also very important. After entering in twenty-first Century, LED's high efficiency, ultra high brightness, color, continuous development and innovation, red, orange LED light efficiency has reached 100Im / W, green LED is 501m / W, the luminous flux of a single LED also reached dozens of Im. LED chips and packages are no longer located along the traditional Gong