In recent years, with the rapid technological development led production to make it luminous brightness enhancement and life extension, plus the cost of production is significantly reduced, and the rapid expansion of LED application market, such as consumer products, signaling systems and general lighting , so the size of the global market The rapid growth. 2003 the global LED market is about $ 4.48 billion ( about $ 2.7 billion) high-brightness LED market growth of 17.3% compared to 2002 (high-brightness LED market growth of 47%), riding the trend of the mobile phone market continues to grow, the forecast 2004 still 14.0 percent growth rate can be expected.
Cell phone, digital camera, PDA, etc. white LED backlight Blu-ray single-chip plus YAG fluorescence from. With the phone flash, medium and large size (NB, LCD-TV, etc.) display light source module, as well as special-purpose lighting system applications gradually increased. Next extended to be used for general lighting system equipment, high-power white LED technology (HighPower) the LED market will have become more obvious. The technical side, the biggest challenges have been encountered and to upgrade and maintain the brightness, if more to enhance its cooling capacity development potential in the market.
ASM has over two decades of experience in R & D and production automation optoelectronic component packaging equipment, the industry's current LED brightness method for a variety of upgrade to the packaging process, from the chip and package design level, to enhance the cooling capacity and increased luminous efficiency goals. In this paper, an overview and discussion on the latest developments and achievements of the LED packaging technology.
Chip design
Evolution chip found major LED manufacturer
s in the upstream epitaxial technical improvements, such as using different electrode design control current density, the use of the ITO film technology to make the current through the LED evenly distributed LED chip structure on as far as possible to produce up to photons. And then use a variety of different approaches to extracting a photon emitted by the LED, such as the production of the different shape of the chips; using chip peripheral effectively control the degree of refraction of light to improve the LED light extraction efficiency, developed to expand the surface of the single-chip size (> 2mm2) increase the luminescence area, more rough surface to increase light revealing. Pn two electrodes in high brightness LED chip position far closer, so that the luminous efficiency and cooling ability. Recently, high-power LED production is the use of new and improved laser to dissolve (Laserlift-off) and the metallic bonding the technology (metalbonding), the LED epitaxial wafer
is removed from the GaAs or GaN crystal growth substrate , and bonding to another or other metal substrate having high reflectivity and high thermal conductivity of the material above, and to help the high-power LED to improve light extraction efficiency and cooling capacity.
Package design
After years of development the the vertical LED lamp (φ3mm, φ5mm) and SMD lights (surface mount LED) has evolved into a standard product model. However, with the development needs of the chip, and open up the the encapsulated products designed to meet the high-power, reduce manufacturing costs in order to take advantage of the automated assembly technology, high-power SMD lamps also came into being. Portable consumer products market, driven by the rapid, high-power LED packaging volume design smaller, the thinner to provide a wider design space.
In order to maintain the finished product in brightness after the package, the new and improved high power LED SMD devices plus cup-shaped reflecting surface will help consistently to all light reflected off the outside of the package in order to increase the output lumens. Cover the LED on the circular optical lens , superior materials change for Silicone sealant instead of epoxy resin (Epoxy) package can maintain a certain durability.
Packaging process and programs
The main purpose of the semiconductor packaging to ensure that between the semiconductor chip and the lower circuit correct electrical and mechanical connecting with each other, and the protection chip to prevent subjected to mechanical, thermal, moisture and other external shocks. Select the encapsulation method, materials and use of the machine to be taken into account the factors of LED epitaxial shape, electrical / mechanical characteristics and solid crystal accuracy. Its optical properties due to LED package to be considered and to ensure that its optical properties can meet.
The vertical LED or SMD LED
package, must choose a high-precision Bonder precise position of the LED chip into the package or not directly affect the luminous efficacy of the whole package devices. Shown in Figure 1, if the position deviation of the chip within the reflective cup, the light has not been fully reflected to affect the brightness of the finished product. However, if a solid crystal machine has advanced pre-image recognition system (PRSystem), despite variations in quality lead frame, can still accurately welded to the the reflective cup predetermined position.
General low power LED devices (such as the pointing device and the phone's keypad lighting) in Silver solid crystal, silver paste itself can not withstand high temperatures, at the same time enhance the brightness fever phenomenon will produce, thus affecting the product. To obtain high quality, high power LED, a new crystalline solid process along developed, wherein one is the use of the eutectic soldering techniques, the first die-bonding at a heat radiation substrate (soubmount) or heat sink (heatsink), and then the whole chip with heat dissipation substrate is then welded to the packaged device, so you can enhance the cooling capacity of the device, so that the relative increase of the luminous power. As for the substrate material, silicon (Silicon), Cu (Copper), and ceramics (Ceramic) are commonly used heat radiation substrate materials.
Eutectic solder
The technology most critical is the choice of materials and welding of the eutectic temperature control. Generation of InGaN high-brightness LED, such as eutectic soldering, the chip may be used at the bottom of the contact surface coating of pure tin (Sn) or gold-tin (Au-Sn) alloy as the chip is plated with gold or silver on the substrate can be welded to. When the substrate is heated to a suitable temperature of the eutectic (Figure 5), the penetration of gold or silver element to the gold-tin alloy layer to improve the melting point, the change in the composition of the alloy layer, the layer is cured and LED fastening eutectic solder in hot sink or on a substrate (Figure 6). Select the eutectic temperature of the chip depending on the heat level of the substrate and device materials and subsequent SMT reflow process temperature requirements. Consider eutectic crystalline solid machine, in addition to the high positional accuracy, another important condition is to have a flexible and stable temperature control, plus a nitrogen gas or a mixed gas apparatus, help in the process of eutectic oxidation protection. Course solid crystal and silver paste to achieve the high-precision solid crystal, depends on rigorous mechanical design and high-precision motor movement, in order that the movement of the welding head and welding force control more than just right, without compromising the high productivity and high yield requirements.
Flux can also be added for eutectic soldering processes, the biggest feature of this technology there is no need for additional welding force, and therefore not solid crystal welding force is too large, too much eutectic alloy overflow to reduce the opportunities generated by the LED short circuit .
Flip chip (FlipChip) Welding
Flip chip welding and has been actively used in the process of high power LED
, flip chip method the GaNLED chips fell bonded to heat the substrate, gold wire pad hindered some help to increase the brightness. Shorten the distance of the current circulation, reduce resistance, so the heat generated is relatively lower. Such bonding is also effective in heat go to the next level of heat dissipation substrate and then go to the device outside. When this technology is applied in SMDLED not only to increase the light output, the more you can make the product as a whole area of narrow, expand the product's application market.
Flip-chip LED technology development, there are two main options: First, the solder ball the welding (Solderbumpreflow); thermosonic (Thermosonic) welding technology. Solder ball welding (Figure 10) in the IC packaging applications for some time, technology has also matured, do not go into details here.
The number of devices for low-cost and low-line production, heat ultrasonic flip chip technology (Thermosonicflipchip) (Figure 11) is especially suitable for high power LED soldering. Gold welding interface design process in the solid crystal gold this thing melting temperature than tin-lead ball and silver paste, more flexible. In addition, lead-free process, the process is simple, reliable metal pick-bit, etc.. Thermal ultrasonic flip chip technology after years of research and experience accumulated, has mastered the optimization of process parameters, and successfully put into mass production in several major LED manufacturers.
Foot production line, a lot of automation equipment (such as chip bonder, wire welding machine, test machine, taping machine), but also all rely on imports.
Specific proposals for development of LDD equipment industry
Suggested the country in support of the LED technology and industrial development, materials and process equipment to support it as a basis for the development and the driving force behind. In the process of the development of LED technology and industry, it is recommended that China take the introduction, digestion, absorption, innovation, improve roads. Specific programs as follows: in the country, supported by the national LED manufacturers and equipment and materials manufacturing tripartite joint establishment of the incubator function LED equipment, materials, manufacturing and application of the Commonwealth.
Mastered in a short period of time and improve equipment manufacturing level, the the driven LED industry development of China's high-grade recommended by the Commonwealth of co-financing (50% of the country, 15% of the equipment research and development unit, chip manufacturing and packaging technology research units 15%, LED chip 20%) of the construction of a complete LED chip
manufacturing and packaging demonstration production line manufacturing and packaging companies. The model line to solve the equipment development and process test LED product manufacturing process technology research and validation sets supply of technology and process equipment. The units involved in the construction of the demonstration, the right to free use of the production line related products, technology and the industrialization of research and test, especially LED production units Preferential get the outcome of the research and industrialization.
The model line, the implementation of the three-step strategy, and ultimately the commercialization of LED production equipment and localization (to see equipment localization program Table II). The first step: the use of about two years, and the localization of some key equipment (countries grant some bonus support); domestic has a certain foundation and the use of common equipment with a cost advantage principle of market competition, take the access system merit-based matching part is difficult, the localization devices can not in the short term, the country should arrange the research, and the completion of the production? prototyping (through the development of standards); Second step, starting from the third year of the implementation of the program, the first step involves the first two types of devices focused on solving the adaptability of the production process, production efficiency, reliability, appearance and cost, with supporting domestic and bulk supply capacity and the research class equipment to complete production prototype development of commercialization (γ-machine). Third step, from the first five years of implementation of this program, the first and the second step involves all equipment with international competitiveness, in addition to meet domestic demand, to occupy certain international markets; research equipment to meet the industrialization production requirements and have the bulk supply capacity.