From the point of view of practical application, installation is simple to use, the relatively small volume of high-power LED devices in most lighting applications will replace traditional power led devices. Small power LED lighting in order to meet the needs of the lighting, the focus must be on many LED light energy in order to meet the design requirements, but the drawback is that the line is very complex, poor heat dissipation, in order to balance the current between each LED voltage relationship, must be designed to the complexity of the power supply circuit. In contrast, the power of the high-power single LED is much larger than the number of small power LED the sum of the power supply line is relatively simple, perfect heat dissipation structure, physical properties and stability. So, packaging methods and packaging materials for high-power LED devices can not simply apply the traditional low-power LED devices and packaging methods and packaging materials. A new and higher requirements for large power dissipation, large heat and high light efficiency to LED packaging technology, packaging equipment and packaging materials.
1. High power LED chip
In order to get a high-power LED devices, it is necessary to prepare a suitable high-power LED chips. The usual method of manufacturing high power LED chip are summarized as follows:
(1) Increase the size of law. By increasing the effective light emitting area and size of single LED, prompting the current flowing through the TCL layers uniformly distributed, in order to achieve the desired luminous flux. However, simply increasing the light-emitting area can not solve the heat problem and the light problem, and not achieve the desired luminous flux and the practical application of the effect.
(2) Silicon backplane flip method. First preparing a large-size LED chip suitable for eutectic soldering, to simultaneously prepare the corresponding size of the silicon substrate and the silicon substrate to produce for eutectic soldering with a gold conductive layer and leads to the electrically conductive layer (Ultrasonic gold ball pads) , and then use the eutectic soldering device of the large-size LED chip and the silicon substrate are welded together. This structure is more reasonable, considering both the light problem, taking into account the heat problem, which is the current mainstream high power LED production.
American Lumileds, developed in 2001 AlGaInN power flip chip (FCLED) structure, the manufacturing process: First, the thickness of greater than 500A NiAu layer deposited on the top of the p-type GaN epitaxial wafers, used for ohmic contact and back reflector; then using a mask to select the P-type layer and multi-quantum well active layer is etched away, exposing the N-type layer; deposition, etching to form the N-type ohmic contact layer, a chip size of 1mm × 1mm, the P-type ohmic contact is square, N-type ohmic contact to comb inserted therein, so that the current extension distance can be shortened, the spreading resistance is minimized; then flip chip soldering metal bumps AlGaInN having anti-static protection diode (ESD) of the The silicon carrier.
(3) ceramic substrate flip. First use of the generic device of the LED chip having a suitable eutectic welding electrode structure of the large out of the light area of the LED chip and the corresponding ceramic base plate was prepared, and on the ceramic substrate produced a eutectic soldering conductive layer and leads to the conductive layer, and then using eutectic soldering The equipment will be large-size LED chip and the ceramic substrate are welded together. This structure not only consider the light problems also take into account the heat problem, and ceramic floor for high thermal conductivity ceramic plates, the cooling effect is very ideal, the price is relatively low, so for more suitable substrate material, and may in the future IC integration package reserved space.
(4) sapphire substrate transition method. InGaN chip in accordance with the traditional method of manufacturing a PN junction is grown on a sapphire substrate, sapphire substrate removal, and then connect to the traditional four-membered, material and manufacture of the large size of the blue LED chip of the upper and lower electrode structures.
(5) The AlGaInN silicon carbide (SiC) on the back light method. Cree Inc., USA is the world's only SiC substrate manufacturing AlGaInN high brightness LED manufacturers, the past few years its production AlGaInN / SiCa chip structure continue to improve brightness and continuously improve. As the P-type and N-type electrode, respectively, located in the bottom and top of the chip, the use of single-wire bonding, better compatibility, ease of use, and thus become another mainstream products of the the AlGaInN LED development.
2. The power-type package
Power LED was first started in the HP "piranhas" package LED structure introduced in the early 1990s, launched the company in 1994 improved "Snap LED" There are two operating current of 70mA and 150mA, input power up to 0.3W. The power LED input power than the original bracket encapsulated LED input power is increased several times, thermal resistance is reduced fraction of the original. W-class power LEDs is a core part of the future of lighting devices, so the world's major companies have invested a great deal of effort watt-level power LED packaging technology research and development.
LED chip and packaging to the direction of the high-power development, large current is 10 to 20 times more than φ5mm LED luminous flux, we must solve the problem of bad light, effective heat dissipation without deterioration of the packaging materials, shell and tube, and the package is its The key technologies, be able to withstand a few watts of power LED packaging. 5W series of white, green, blue-green, blue power LED from early 2003 to market, white LED light output of 187lm luminous efficiency for 44.3lm / W. Developed can withstand 10W power LED, the use of a large area of the die size of 2.5mm × 2.5 mm in 5A current, light output up to 200lm.
LUXEON series power LED the AlGaInN power-type flip-die flip chip bonding with solder bumps on the silicon carrier, and then the completion of the flip chip bonding silicon carrier loaded in the thermal liner and the shell, the bonding wires to be encapsulated. This encapsulation of the light extraction efficiency, thermal properties, and are designed to increase the operating current density.
In the application, can be encapsulated product assembly in a metal core PCB, with aluminum interlayer, forming power density type LED PCB board as the wiring of the device electrodes is connected to use, the aluminum sandwich can be used as a thermal liner to to obtain a higher luminous flux and photoelectric conversion efficiency. In addition, the encapsulated SMD LED very small, and can be flexibly combined, constitute a module type light guide plate-type condenser type, reflective type colorful lighting source.
High brightness LED lights and other auxiliary lighting source applications, generally the multiple Φ5mm package a variety of monochrome and white LED assembly on a lamp panel or standard lamp holder, life can reach 100,000 hours. 2000 studies have pointed out the white LED work 6000h in Φ5mm, its intensity has been reduced to half its original. In fact, the use of Φ5mm white LED array light-emitting device, its life may be 5000h. Different color LED light attenuation at different speeds, the slowest which red, blue, green center, white fastest. Used only for indicator LED original Φ5mm package, package thermal resistance up to 300 ° C / W, can not be fully heat dissipation, resulting in elevated temperature of the LED chip, causing the devices optical attenuator accelerated. In addition, the epoxy yellowing will reduce the light output. High Power LED generated in the high current white LED is 10 to 20 times more luminous flux than Φ5mm effective thermal design and the use of packaging material does not deteriorate to solve the problem of bad light, shell and tube, and the package has become the development of high-power LED one of the key technologies. New LED power-type packaging design concept mainly grouped into two categories, a class of single-chip power package, and the other for multi-chip power package.
(1) Single-chip power type LED package
1998 American Lumileds developed Luxeon high-power LED series single-chip package structure, this power single-chip LED package structure with conventional Φ5mm LED package structure is completely different, it is a positive light LED chip soldered directly to the thermal liner The LED chip, or on the back of light first flip-chip having solder bumps on the silicon carrier, and then welding on the thermal liner, so that large area chips in the large current, the thermal characteristics of the work is improved. This package light extraction efficiency, thermal performance and current density of the design are the best, its main features are:
A. Low thermal resistance. The conventional epoxy Packaging has high thermal resistance, and thermal resistance of this new structure of a package is typically only 14 ° C / W, can be reduced to 1/20 of the conventional LED.
B. High reliability. Filled inside a stable, flexible gel, at 40 to 120 ° C, the internal stress generated due to sudden changes in temperature will not make the gold and the frame lead is disconnected. With this silicone rubber as the sealing material of the optical coupling, does not appear as yellowing of ordinary optical epoxy, the metal lead frame is also not due to oxidation and dirt.
C. Reflector cup and lens design so that the radiation controlled, the highest optical efficiency. In applications they can be assembled in one with aluminum interlayer circuit board (aluminum PCB) on the circuit board as the wiring of the device electrodes is connected with the the aluminum sandwich can be as a power type LED thermal liner. So that not only a high luminous flux can be obtained, but also has a high photoelectric conversion efficiency.
Single-chip W-class power LED was first introduced in 1998 by Lumileds Luxeon LED, the characteristics of the package structure thermoelectric form of separation, the flip-chip silicon carrier is soldered directly to the thermal liner and reflective cup optical lens and a flexible transparent plastic new structures and new materials, high-power single-chip 1W, 3W and 5W LED products are available now. OSRAM 2003 Golden Dragon series of single-chip LED, its structure is characterized by a thermal liner is in direct contact with the metal circuit board has good heat dissipation, input power up to 1W.
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