At present, the lighting industry has some obvious limitations. Incandescent bulbs are very inefficient, and the bulb converts up to 90% of the energy into heat, which is emitted from the filament. Although the sales of energy-saving lamps (also known as "compact fluorescent lamps") seem to be better (because the lamp life is longer and more efficient), it is not a long-term solution because it contains mercury, so it will be cleaned and Destruction brings certain problems.
The consensus is that the lighting industry is headed by high-brightness LEDs (HB-LEDs). The main strengths of HB-LED are: high energy efficiency / low power consumption; very long working time (up to 100,000 hours); can change the direction of illumination, improve system efficiency; stable, anti-vibration, cold light source, touch safety; The color of the light is saturated and bright; when it is operated, it is on and off.
According to analysis by market research firm Strategies Unlimited, the overall market for HB-LEDs has increased by 50% since 1995; and for HB-LED applications in lighting, the market has grown by 60 over the past three years. %. It is expected that there will be a 12% growth rate in 2008 alone. By 2012, the packaged HB-LED market is expected to reach 11.4 billion. The lighting technology industry is rapidly evolving in this field, and its potential applications are very broad, far exceeding traditional home and industrial applications, entering the lighting of medical instruments, automotive and construction, backlighting of displays and many others. In the consumer goods.
Due to its wide range of applications, HB-LED brings many challenges to the manufacturing industry. They are produced by complex epitaxial growth techniques, such as metal organic chemical vapor deposition (MOCVD), which is very complex and relies on chemical reactions to achieve crystal growth rather than physical deposition. Because the powder content of the diode is very high, HB-LED requires a heat sink, which can lower the temperature of the device and effectively dissipate heat to optimize the performance of the device. It is very important to effectively dissipate heat, which ensures that the LED can work normally for a long time. The heat sink is made of highly thermally conductive copper, molybdenum, or alloys thereof (such as copper-tungsten alloy) to maintain the life of the device and to ensure a higher output of luminosity.
However, how to reduce the cutting cost of these metals has become an urgent problem to be solved, because the conventional cutting technology may cause damage or pollution, which not only hinders the processing process, but also affects the performance and efficiency of the LED.
Cutting method
When mechanical cutting (saw blade) is used, the metal used as the heat sink wears the sawtooth on the diamond saw blade more seriously than the conventional wafer packaging. Because the diamond particles have resin, the resin will attract small particles on the soft metal. The granules run into the gaps in the saw blade, making the saw blade dull. In this way, the saw blade must be replaced frequently, which is quite expensive. Moreover, the diamond saw blade brings serious pollution because the small particles return to the surface of the material if they are not attached to the saw blade. This will significantly reduce the luminosity and thus the efficiency of the HB-LED. Although the saw blade can be processed very quickly, these problems can cause the saw blade to break quickly. If they are optimized to improve the quality of the cut, the processing speed is very slow and does not meet the production needs. The impact on the entire production process makes the cost of diamond saw blades too high in this application.
Infrared (IR) or green "dry" lasers generate a lot of thermal energy and correspondingly cause thermal damage to the soft metal used in the HB-LED heat sink. These metals are difficult to disperse easily after they become in a plasma state, and they remain in the slits, forming burrs or recast layers, which hinder the separation of the mold. Increasing the jet intensity does not improve the plasma removal efficiency. Instead, it shifts the recast layer from the slit to the active area of ​​the HB-LED array, reducing the output. This jeopardizes the functionality and efficiency of the device and increases the operating costs of device manufacturers when using laser technology.
Ultraviolet (UV) lasers operate more efficiently than infrared and green lasers because they generate more thermal energy during operation, however, they are processed for the thickness of the material to be processed (100-500 m). The speed is too slow. Even when the power is small, they still produce some thermal damage and pollution. In summary, due to the large size of the heat-affected zone (HAZ) (up to 60m), the edge quality obtained by using conventional lasers to cut HB-LED metal has not been able to meet market demand.
The third technique is the use of a micro water jet laser. The laser was patented and put on the market by Synova. The English name of the product is LaserMicroJet, which means "laser micro water knife". At the beginning, the technology was used in medical equipment, and it is currently used in semiconductors and electronic devices. Precision micromachining. This technology uses an ultra-fine, low-pressure water stream to direct the laser beam onto the surface of the material. The processing technology and performance of this processing technology is very different from traditional dry lasers.
First, because the water flow is cylindrical and the laser beams are parallel, the walls of the slit are parallel. The working distance depends on the stable distance of the water flow and can be several centimeters long, so there is no need to control the focusing process. The laser remains focused in the water stream.
Second, the technique does not suffer from thermal damage because the water stream cools the slit between the laser pulses. The temperature at the edge of the slit drops to the water temperature, and any thermal energy due to laser processing is not conducted inside the material. This effectively avoids damage caused by heating, such as micro-cracks, oxidation, structural changes, or low mold fracture stress. And the area of ​​HAZ is reduced by ten times.
Third, the micro water knife greatly reduced the degree of pollution. The water pressure is typically 50-500 bar, which allows the micro water knife to have enough energy to remove the molten material. At the same time, because the micro water jet is very thin (about 20-100 m in diameter), the mechanical force on the wafer is negligible (less than 0.1 N), so there are no debris or micro cracks in the entire process.
Fourth, the micro water jet has a high energy, which makes the cutting process of molten metal easier and faster - the metal up to 600m can be cut in 1-3 seconds, and the cutting edge is smooth and tidy, not only processing The results are consistent and of high quality (see Figure 1). The micro water jet can cut the HB-LED into any shape: square, round, hexagonal, etc. (see Figure 2). This makes the use of materials more efficient and reduces waste. Depending on the needs, people need to use LEDs of different shapes. Micro waterjets are ideal for this application. In addition, since the micro water jet can quickly cool and wash the residual particles, the particles no longer adhere to the surface of the wafer, so the contamination is almost eliminated. Table 1 shows the cutting and processing capabilities of the micro-waterjet laser for different sizes and thicknesses of copper-based HB-LEDs.
Meet the latest requirements
Currently, there are several different ways to process/package HB-LEDs. The first way is to mount the active components on the metal wafer and then cut the wafer into individual small wafers. Effective cutting of these materials is very difficult because they are too heavy for infrared or green lasers. Both types of lasers use a gas stream to blow away the molten material, but the energy generated by the gas stream is not sufficient for this application. Moreover, during the cutting process, the high energy generated by the laser burns the edges of the material, causing damage that cannot be repaired.
Another method is to mount the LED components on a sapphire or silicon carbide wafer and then cut the LEDs with a saw blade. Since the cooling process is not fast enough, the manufacturer fabricates the HB-LEDs in an array, which is covered with copper and then The material is polished to obtain a pure copper wafer containing HB-LEDs with only the illuminated surface exposed to the copper material. Micro waterjet lasers are ideal for cutting these mounted wafers because they have a unique package and a large number of heat sinks that can easily be damaged if processed in other ways.
* The results of sample 4 are shown in Figure 1.
At present, in many countries, people are developing national-level development plans to expand the range of applications of LEDs as a means of illumination. These countries include countries with significant technological development potential in the United States and Asia, such as Japan, Taiwan, South Korea, and China. Since lighting accounts for 20% of total electricity consumption, these developments aim to save energy on a large scale, help consumers reduce electricity costs, and reduce the greenhouse effect by reducing emissions. However, the biggest driving force in the HB-LED lighting market is that they can adapt to some new applications. In these new applications, it is possible that traditional lighting devices have obvious disadvantages, and the reliability and other special factors of LEDs may be Make traditional equipment unable to compete with it. With the rapid growth of the HB-LED market, the market for micro-waterjet lasers is also expected to increase rapidly.
The consensus is that the lighting industry is headed by high-brightness LEDs (HB-LEDs). The main strengths of HB-LED are: high energy efficiency / low power consumption; very long working time (up to 100,000 hours); can change the direction of illumination, improve system efficiency; stable, anti-vibration, cold light source, touch safety; The color of the light is saturated and bright; when it is operated, it is on and off.
According to analysis by market research firm Strategies Unlimited, the overall market for HB-LEDs has increased by 50% since 1995; and for HB-LED applications in lighting, the market has grown by 60 over the past three years. %. It is expected that there will be a 12% growth rate in 2008 alone. By 2012, the packaged HB-LED market is expected to reach 11.4 billion. The lighting technology industry is rapidly evolving in this field, and its potential applications are very broad, far exceeding traditional home and industrial applications, entering the lighting of medical instruments, automotive and construction, backlighting of displays and many others. In the consumer goods.
Due to its wide range of applications, HB-LED brings many challenges to the manufacturing industry. They are produced by complex epitaxial growth techniques, such as metal organic chemical vapor deposition (MOCVD), which is very complex and relies on chemical reactions to achieve crystal growth rather than physical deposition. Because the powder content of the diode is very high, HB-LED requires a heat sink, which can lower the temperature of the device and effectively dissipate heat to optimize the performance of the device. It is very important to effectively dissipate heat, which ensures that the LED can work normally for a long time. The heat sink is made of highly thermally conductive copper, molybdenum, or alloys thereof (such as copper-tungsten alloy) to maintain the life of the device and to ensure a higher output of luminosity.
However, how to reduce the cutting cost of these metals has become an urgent problem to be solved, because the conventional cutting technology may cause damage or pollution, which not only hinders the processing process, but also affects the performance and efficiency of the LED.
Cutting method
When mechanical cutting (saw blade) is used, the metal used as the heat sink wears the sawtooth on the diamond saw blade more seriously than the conventional wafer packaging. Because the diamond particles have resin, the resin will attract small particles on the soft metal. The granules run into the gaps in the saw blade, making the saw blade dull. In this way, the saw blade must be replaced frequently, which is quite expensive. Moreover, the diamond saw blade brings serious pollution because the small particles return to the surface of the material if they are not attached to the saw blade. This will significantly reduce the luminosity and thus the efficiency of the HB-LED. Although the saw blade can be processed very quickly, these problems can cause the saw blade to break quickly. If they are optimized to improve the quality of the cut, the processing speed is very slow and does not meet the production needs. The impact on the entire production process makes the cost of diamond saw blades too high in this application.
Infrared (IR) or green "dry" lasers generate a lot of thermal energy and correspondingly cause thermal damage to the soft metal used in the HB-LED heat sink. These metals are difficult to disperse easily after they become in a plasma state, and they remain in the slits, forming burrs or recast layers, which hinder the separation of the mold. Increasing the jet intensity does not improve the plasma removal efficiency. Instead, it shifts the recast layer from the slit to the active area of ​​the HB-LED array, reducing the output. This jeopardizes the functionality and efficiency of the device and increases the operating costs of device manufacturers when using laser technology.
Ultraviolet (UV) lasers operate more efficiently than infrared and green lasers because they generate more thermal energy during operation, however, they are processed for the thickness of the material to be processed (100-500 m). The speed is too slow. Even when the power is small, they still produce some thermal damage and pollution. In summary, due to the large size of the heat-affected zone (HAZ) (up to 60m), the edge quality obtained by using conventional lasers to cut HB-LED metal has not been able to meet market demand.
The third technique is the use of a micro water jet laser. The laser was patented and put on the market by Synova. The English name of the product is LaserMicroJet, which means "laser micro water knife". At the beginning, the technology was used in medical equipment, and it is currently used in semiconductors and electronic devices. Precision micromachining. This technology uses an ultra-fine, low-pressure water stream to direct the laser beam onto the surface of the material. The processing technology and performance of this processing technology is very different from traditional dry lasers.
First, because the water flow is cylindrical and the laser beams are parallel, the walls of the slit are parallel. The working distance depends on the stable distance of the water flow and can be several centimeters long, so there is no need to control the focusing process. The laser remains focused in the water stream.
Second, the technique does not suffer from thermal damage because the water stream cools the slit between the laser pulses. The temperature at the edge of the slit drops to the water temperature, and any thermal energy due to laser processing is not conducted inside the material. This effectively avoids damage caused by heating, such as micro-cracks, oxidation, structural changes, or low mold fracture stress. And the area of ​​HAZ is reduced by ten times.
Third, the micro water knife greatly reduced the degree of pollution. The water pressure is typically 50-500 bar, which allows the micro water knife to have enough energy to remove the molten material. At the same time, because the micro water jet is very thin (about 20-100 m in diameter), the mechanical force on the wafer is negligible (less than 0.1 N), so there are no debris or micro cracks in the entire process.
Fourth, the micro water jet has a high energy, which makes the cutting process of molten metal easier and faster - the metal up to 600m can be cut in 1-3 seconds, and the cutting edge is smooth and tidy, not only processing The results are consistent and of high quality (see Figure 1). The micro water jet can cut the HB-LED into any shape: square, round, hexagonal, etc. (see Figure 2). This makes the use of materials more efficient and reduces waste. Depending on the needs, people need to use LEDs of different shapes. Micro waterjets are ideal for this application. In addition, since the micro water jet can quickly cool and wash the residual particles, the particles no longer adhere to the surface of the wafer, so the contamination is almost eliminated. Table 1 shows the cutting and processing capabilities of the micro-waterjet laser for different sizes and thicknesses of copper-based HB-LEDs.
Meet the latest requirements
Currently, there are several different ways to process/package HB-LEDs. The first way is to mount the active components on the metal wafer and then cut the wafer into individual small wafers. Effective cutting of these materials is very difficult because they are too heavy for infrared or green lasers. Both types of lasers use a gas stream to blow away the molten material, but the energy generated by the gas stream is not sufficient for this application. Moreover, during the cutting process, the high energy generated by the laser burns the edges of the material, causing damage that cannot be repaired.
Another method is to mount the LED components on a sapphire or silicon carbide wafer and then cut the LEDs with a saw blade. Since the cooling process is not fast enough, the manufacturer fabricates the HB-LEDs in an array, which is covered with copper and then The material is polished to obtain a pure copper wafer containing HB-LEDs with only the illuminated surface exposed to the copper material. Micro waterjet lasers are ideal for cutting these mounted wafers because they have a unique package and a large number of heat sinks that can easily be damaged if processed in other ways.
* The results of sample 4 are shown in Figure 1.
At present, in many countries, people are developing national-level development plans to expand the range of applications of LEDs as a means of illumination. These countries include countries with significant technological development potential in the United States and Asia, such as Japan, Taiwan, South Korea, and China. Since lighting accounts for 20% of total electricity consumption, these developments aim to save energy on a large scale, help consumers reduce electricity costs, and reduce the greenhouse effect by reducing emissions. However, the biggest driving force in the HB-LED lighting market is that they can adapt to some new applications. In these new applications, it is possible that traditional lighting devices have obvious disadvantages, and the reliability and other special factors of LEDs may be Make traditional equipment unable to compete with it. With the rapid growth of the HB-LED market, the market for micro-waterjet lasers is also expected to increase rapidly.
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