With the use of mobile flash, large and medium size (NB, LCD-TV, etc.) display light source module and even special purpose lighting system applications gradually increased. And then extended to the general lighting system equipment, the use of white LED technology, high power (High Power) LED market will continue to show. In terms of technology, the biggest challenge is to enhance and maintain the brightness, if further enhance its cooling capacity, the development of the market potential.
With the increasing application of mobile flashlight, large and medium sizes displays (NB, LCD-TV), illumination system in special usage and other future devELopment in illumination devices, high power LED with white light LED in the market in succession. Challenge present is how to raise and keep the brightness. If the capability of heat radiating can be boosted up, the technology will have more powerful market potential.
In recent years, with the development of LED production technology, so that its luminous brightness and life expectancy, coupled with significantly reduced production costs, the rapid expansion of the LED application market, such as consumer products, signal systems and general lighting, so its global market size growing up very fast. In 2003, the global LED market was about US $ 4.48 billion (high-brightness LED market of about US $ 2.7 billion), up 17.3% over 2002 (high brightness LED market grew by 47%), and the mobile phone market continued to grow. 14.0% growth rate can be expected.
In product development, the white LED research and development has become the focus of the development of the project. There are four main ways to make white LED:
One, blue LED + yellow fluorescent powder (such as: YAG)
Second, red LED + green LED + blue LED
Third, the UV LED + red / green / blue light of the phosphor
Four, blue LED + ZnSe single crystal substrate
At present, mobile phones, digital cameras, PDA and other backlight used by the white LED with blue single crystal plus YAG fluorescent. With the use of mobile flash, large and medium size (NB, LCD-TV, etc.) display light source module and even special purpose lighting system applications gradually increased. And then extended to the general lighting system equipment, the use of white LED technology, high power (High Power) LED market will continue to show. In terms of technology, the biggest challenge is to enhance and maintain the brightness, if further enhance its cooling capacity, the development of the market potential.
With more than 20 years of experience in R & D and production of automated optoelectronic components packaging, ASM has a number of ways to enhance LED brightness, both from the chip and packaging design, to the packaging process to enhance the cooling capacity and increase the luminous efficiency as the goal The In this paper, the latest development and results of LED packaging technology for a brief introduction and discussion.
From the evolution of the chip found that the major LED manufacturers in the upstream epitaxy technology continues to improve, such as the use of different electrode design to control the current density, the use of ITO thin film technology to make the average current distribution through the LED, LED chip in the Structures are as much as possible to produce the most photons. And then use a variety of different methods to extract the LED issued by each of the photons, such as the production of different shapes of the chip; the use of the chip around the effective control of light refraction to improve the efficiency of LED light extraction, development and expansion of a single chip surface size (> 2mm2) Area, and more use of rough surface to increase the light and so on. There are some high-brightness LED chip p-n two electrodes closer to the location, so that the chip luminous efficiency and cooling capacity. The recent production of high-power LEDs is the use of new modified laser lift-off and metal bonding to remove LED epitaxial wafers from GaAs or GaN long crystal substrates and to bond To another metal substrate or other high reflectivity and high thermal conductivity of the material above, to help high-power LED to improve the efficiency of light extraction and cooling capacity.
After years of development, vertical LED lights (φ3mm, φ5mm) and SMD lamps (surface mount LEDs) have evolved into a standard product model. But with the development and needs of the chip, to develop a high-power packaging products designed, in order to use automated assembly technology to reduce manufacturing costs, high-power SMD lights also came into being. Moreover, in the portable consumer products market driven by the rapid, high-power LED package volume design is also smaller and thinner to provide a wider product design space.
In order to keep the finished product in the package after the brightness, the new improved high-power SMD devices with a cup-shaped reflective surface, will help all the light can be reflected in the package to increase the output lumen. And cover the LED on the circular optical lens, the material used to change Silicone sealant, instead of the previous epoxy (Epoxy), so that the package can maintain a certain degree of durability.
Packaging technology and programs
The main purpose of the semiconductor package is to ensure the correct electrical and mechanical interconnection between the semiconductor chip and the underlying circuit, and to protect the chip from mechanical, thermal, moisture and other external shocks. Selection of packaging methods, materials and the use of the machine, to take into account the LED epitaxial shape, electrical / mechanical properties and solid crystal precision and other factors. Because the LED has its optical characteristics, the package must also be considered and ensure that it can meet the optical characteristics.
Whether it is vertical LED or SMD package, must choose a high-precision solid crystal machine, because the LED grain into the package position is accurate or not directly affect the overall package device luminous efficiency. As shown in Figure 1, if the grain in the reflective cup position deviation, the light can not be completely reflected, affecting the finished product brightness. However, if a solid crystal machine has an advanced pre-image recognition system (PR System), although the quality of the lead frame, can still be accurately welded to the reflective cup within the predetermined location.
General low-power LED devices (such as indicating the equipment and mobile phone keyboard lighting) is mainly silver paste solid crystal, but because the silver itself can not withstand high temperatures, while enhancing the brightness of the heat phenomenon will occur, thus affecting the product. To obtain high-quality high-power LED, the new solid crystal process along with the development, one of which is the use of eutectic welding technology, the first grain welding in a heat board (soubmount) or heat sink (heat sink) , And then the whole piece of grain with the cooling plate and then welded to the packaging device, so that the device can enhance the heat dissipation capacity, so that the relative increase in luminous power. As for the substrate material, silicon (Silicon), copper (Copper) and ceramic (Ceramic), etc. are commonly used in the heat of the substrate material.