The evolution process from the chip found in the major LED manufacturers in the upstream epitaxy continuous technical improvements, such as the use of different electrode designs control the current density, the use of ITO thin film technology to make current through the LED can be evenly distributed, so that the structure produce the most as far as possible. 2mm2）增加發(fā)光面積" yd="Then use a variety of different ways to extract every grain of the LED photon, such as the production of different shape of the chip; effectively control the use of chip peripheral increase LED light refraction to take the rate of development to expand the surface of a single chip size (> 2mm2) increase in emitting area " xd="再運用各種不同方法去抽出LED發(fā)出的每一粒光子，如生產(chǎn)不同外形的芯片；利用芯片周邊有效地控制光折射度提高LED取率，研制擴大單一芯片表面尺寸（>2mm2）增加發(fā)光面積" closure_uid_1j4bk6="716">Then use a variety of different ways to extract every grain of the LED photon, such as the production of different shape of the chip; effectively control the use of chip peripheral increase LED light refraction to take the rate of development to expand the surface of a single chip size (> 2mm2) increase in emitting area more use of the rough surface to increase light revealed, and so on.
There are some high-brightness LED chips on the location of pn two electrodes separated by narrow, so that the chip light-emitting efficiency and heat dissipation capacity. The recent production has been, is to use the new improved solution (Laserlift-o) and metal bonding technology (metalbonding), the LED epitaxial wafers from GaAs or GaN crystal growth substrate removed and the metal bonding to another substrate or the other with high reflectance and high thermal conductivity of the material above, to help improve the light extraction efficiency LED power and cooling capacity.
Package Design
After years of development, vertical (φ3mm, φ5mm) and SMD LED (Surface Mount LED) has evolved into a standard product model. But with the development of the chip and needs to develop a product designed to meet high-power package, the use of automated assembly techniques to reduce manufacturing cost, high-power SMD LED has emerged. Moreover, in portable consumer products market, driven by rapid, high-power LED package size of the smaller thinner design to provide a wider design space.
In order to maintain the product in the package after the brightness, the new and improved high-power SMD components have been added to cup-shaped reflector, can help put all the light reflecting consistently outside the package to increase output. The LED on the circular cover, selected materials for Silone sealed plastic changes, instead of the past in epoxy resin (Epoxy), the package can maintain a certain durability.
Packaging technology and programs
The primary purpose of packaging is to ensure that the lower semiconductor chip and the circuit between the electrical and mechanical proper follow each other, and to protect the chip to prevent its being mechanical, heat, moisture, and other various external shocks. Choose packaging methods, materials and the use of machine time, taking into account the shape of LED epitaxy, electrical / mechanical properties and accuracy of solid crystal and other factors. LED has its optical properties due to the package also should be considered and to ensure that its optical characteristics can be met.
Both the vertical LED or SMD package, you must select a high-precision solid crystal, LED die into the package because of the location is accurate or not directly affect the performance of the whole package light emitting device. If the grain position within the reflector cup deviation, not fully reflected light, affecting the brightness of the finished product. However, if a solid crystal with advanced image recognition system in advance (PRSystem), despite the mixed quality of the lead frame, able to accurately pre-welded at the location reflected on the cup.
Generally low-power LED devices (such as the pointing device and keypad lighting) mainly crystalline solid silver, but silver itself can not withstand high temperatures, to enhance the brightness in the same time, the phenomenon will produce heat, which affect the product. To obtain high-quality high-power LED, along with new solid crystal technology were developed, one of which is the use of eutectic welding technology, welding in the first heat grain substrate (soubmount) or heatsink (heatsink), and Then the whole grain with heat welded to the substrate and then packaged devices, so devices can enhance the cooling capacity, so that the relative increase in fat. As substrate materials, silicon (Silicon), Copper (Copper) and ceramic (Ceramic) are all commonly used cooling the substrate material.
Eutectic solder
The key technology is the choice of materials and eutectic solder temperature control. A new generation of high-brightness InGaN LED, such as the use of eutectic solder, grain at the bottom can be used pure tin (Sn) or gold-tin (Au-Sn) alloy for the contact surface coating, the grain can be welded to plated with gold or silver substrate on. When the substrate is heated to a suitable eutectic temperature, the gold or silver elements penetrate into the gold-tin alloy layer, the alloy layer composition changes to improve the melting point, so that eutectic solidification and LED heat sink fastening or welding on the substrate .
Selection depends on the grain eutectic temperature, substrate and device materials, heat resistance and subsequent SMT reflow process when the temperature requirements. Consider the eutectic solid crystal machine, in addition to the high position accuracy, another important condition is to have a flexible and stable temperature control, plus a nitrogen or mixed gas installations, help eutectic process for oxidation protection. Solid crystal and silver, as of course, to achieve high-precision solid crystal, depends on the precise mechanical design and high-precision motor sports, in order to make welding and welding force control head movement just right, apart from non-destructive high productivity and high yield requirements.
The eutectic flux may be added when the welding process, the biggest feature of this technology is no extra additional welding power, welding solid crystal therefore will not force too much too large to make the eutectic alloy overflow, reducing the chance of a shorted LED .
Flip Chip (FlipChip) welding
In recent years, flip chip soldering has been actively applied to high-power LED manufacturing process, flip chip bonding method to GaNLED grains in cooling down the substrate, because there is no obstruction of gold wire bonding pad, to improve the brightness of some help. Because the current flow to reduce the gap to reduce resistance, so heat generation is relatively lower. While such bonding are also effective in the heat transferred to the next level of heat to the device substrate and then go outside. When this process is applied not only to improve light output, but also reduce the area of ??the product as a whole, expanding the application of the product market.
Flip-chip LED technology has two main programs: one solder ball bonding (Solderbumpreflow) technology; the other is thermal ultrasound (Thermosonic) welding.
Tin-lead solder ball has been a long time in the IC packaging applications, technology has matured, so in this repeat. Lines for low cost and low production of the device, thermal ultrasonic flip-chip (Thermosonicflipchip) high-power LED technology is especially suitable for welding. Made welded to gold, because gold itself, the melting temperature of this material than tin and silver high-ball, the solid crystal after the design process more flexible.
In addition, lead-free manufacturing process, process simple, metal bits and reliable. Ultrasonic flip chip process after hot years of research and experience accumulated, has mastered the optimal process parameters, but also in several major LED manufacturers has been successfully put into production. Full production line, the other large (such as chip Bonder, wire welding machine, machine, tape machine) and other automated equipment, but also all imported.
