09/27/2016 Lepower 0
With penetration rate of rapid improvement of the LED commercial lighting and home lighting, continuing to drive the growing market demand. Packaging has also begun to gradually standardize. So far the popular package in LED lighting market mainly by PPA or PCT package of small and medium power products, EMC package of high power and traditional ceramic package of high-power LED and COB package
High-power LED packaging as an important link in the industry chain, is to promote semiconductor lighting and display to practical core manufacturing technology. Only through the development of low thermal resistance, high efficiency and high reliability LED packaging and manufacturing technology, to make the LED chip for good mechanical and electrical protection, to reduce mechanical, electrical, thermal, humidity and other external factors on the chip performance, to protect the LED Chip stable and reliable work in order to provide efficient and sustained high-performance lighting and display effects, to achieve LED-specific advantages of energy-saving lifetime, and promote the sound development of the semiconductor lighting and display industry chain.
Packaging process technology plays a crucial role in LED performance. The choice of LED packaging methods, materials, structure and process are mainly decided by the chip structure, optoelectronic / mechanical properties, the specific application and cost and other factors. With the increase of power, especially the demand for the development of solid-state lighting technology, new and higher requirements are put forward on the optical, thermal, electrical and mechanical structures of the LED package. In order to effectively reduce the package thermal resistance, improve the light efficiency, we must adopt a new technical ideas for package design. At present, the main development trends of power LED package structure are as follows: miniaturization of dimensions, minimization of thermal resistance of devices, planarization of SMD, maximization of withstand junction temperature and maximization of single lamp flux; the goal is to improve luminous flux, efficiency and reduce light failure, failure rate, improved consistency and reliability. For example, the flip-chip EMC series FE35 of Lepower up to 3W and luminous flux of 400lm, realizing a high lumen output with small luminous surface. Specifically, the key technologies of high-power LED package include: Heat disspersion technology, optical design technology, structural design technology, phosphor coating technology, eutectic solder technology.
1.Heat dissipation technology
General LED node temperature can not exceed 120 ℃, so the heat radiation effects of LED devices can be negligible, the heat conduction and convection is the main method of LED cooling. Bonding material, the substrate is a key part of LED cooling technology.
Bonding materials include thermal plastic, conductive silver paste and alloy solder in three main ways.
Substrates include ceramic substrates, metal substrates and composite substrates in three main ways. Ceramic substrates are mainly LTCC substrate and AIN substrate. At present, Lepower COB second-generation COB products mainly use the mirror aluminum plate and copper substrate, such as 4046 mirror aluminum series up to 175lm / w.
2.Optical design technology
The optical design of the LED package includes the inner optical design and the outer optical design.
The key to the optical design is the choice and application of potting. The choice of potting requires its high transmittance, high refractive index, thermal stability, good liquidity, easy to spray. In order to improve the reliability of LED package, but also require potting with low moisture absorption, low stress, temperature and environmental protection and other characteristics. Currently used potting include epoxy resin and silicone. Silicone is obviously superior to epoxy resin, widely used in high-power LED package.
Outer optical design refers to the convergence of the outgoing beam, shaping, in order to form a light field uniform distribution of light. Including the reflective condenser cup design (primary optical) and plastic lens design (secondary optics), the array module, also includes the distribution of the chip array.
Lens shape commonly used convex lens, concave lens, spherical mirror, Fresnel lens, modular lens, etc., Lepower patented moding technology to improve one-time 10-15% of the light output, while easy to secondary light.
3.Structural design technology
LED packaging structure design technology has a pin, power package, SMD, chip-on-board (COB) four stages.
4.Phosphor coating technology
Light conversion structure, namely phosphor coating structure, mainly for LED white lighting technology, the purpose is to LED light emitted by the shorter wavelength of light into complementary (complementary to form white light) of the longer wavelength of light.
5.Eutectic solder technology
Eutectic solder technology is one of the most critical core technologies in high-power LED flip-chip packaging. Eutectic solder technology in the LED packaging process, the core of heat dissipation issue and the advantages of die bond problems, is and will become the mainstream of the future development of LED packaging direction. Eutectic alloys have a lower melting point than pure components and a simple melting process. Eutectic alloys have better fluidity than pure metals and prevent dendrite formation that impedes liquid flow during solidification, thereby improving casting performance. Eutectic alloys Also has a constant temperature transition characteristics (no solidification temperature range), can reduce the casting defects, such as segregation and shrinkage; solidified eutectic alloy strong toughness (close to the toughness of the metal), should not be broken; eutectic coagulation can obtain a variety of forms Of the microstructure, especially the regular arrangement of layered or rod eutectic structure, can be excellent performance in-situ composites. Because of the many benefits of eutectic, LED packages manufactured using eutectic processes have the advantage of reducing impedance and increasing thermal conduction efficiency.