How LED is made?

What is an LED chip? What are its characteristics? LED chip manufacturing is mainly for the manufacture of effective and reliable low-ohmic contact electrodes, and can meet the relatively small voltage drop between contactable materials and provide pressure pads for bonding wires. As much light as possible. The film-transition process generally uses vacuum evaporation method, under 4Pa high vacuum, the material is melted by resistance heating or electron beam bombardment heating method, and BZX79C18 becomes metal vapor deposited on the surface of semiconductor material under low pressure

What is an LED chip? What are its characteristics? LED chip manufacturing is mainly for the manufacture of effective and reliable low-ohmic contact electrodes, and can meet the relatively small voltage drop between contactable materials and provide pressure pads for bonding wires. As much light as possible. The film-transition process generally uses vacuum evaporation method. Under 4Pa high vacuum, the material is melted by resistance heating or electron beam bombardment heating method, and BZX79C18 turns into metal vapor and deposits on the surface of semiconductor material under low pressure.

The commonly used P-type contact metals include AuBe, AuZn and other alloys, and the N-face contact metal often uses AuGeNi alloy. The alloy layer formed after coating also needs to expose as many light-emitting areas as possible through the photolithography process, so that the remaining alloy layer can meet the requirements of an effective and reliable low-ohmic contact electrode and wire bonding pad. After the lithography process is completed, an alloying process is also adopted, which is usually carried out under the protection of H2 or N2. The time and temperature of alloying are usually determined according to factors such as semiconductor material characteristics and alloy furnace form. Of course, if the chip electrode process of blue and green is more complicated, it is necessary to increase the passivation film growth and plasma etching process.

In the LED chip manufacturing process, which processes have a more important influence on its photoelectric performance?

Generally speaking, after the LED epitaxial production is completed, her main electrical properties have been finalized. The chip manufacturing does not change the nature of its production core, but inappropriate conditions in the coating and alloying process will cause some electrical parameters to be bad. For example, a low or high alloying temperature will cause poor ohmic contact. Poor ohmic contact is the main reason for the high forward voltage drop VF in chip manufacturing. After cutting, if some etching process is performed on the edge of the chip, it will help to improve the reverse leakage of the chip. This is because after cutting with a diamond grinding wheel blade, more chip powder will remain on the edge of the chip. If these stick to the PN junction of the LED chip, it will cause leakage and even breakdown. In addition, if the photoresist on the surface of the chip is not stripped cleanly, it will cause difficulties in front bonding wires and virtual soldering. If it is on the back, it will cause a high pressure drop. In the chip production process, the light intensity can be increased by roughening the surface and dividing it into an inverted trapezoidal structure.

Why should LED chips be divided into different sizes? What effect does the size have on the photoelectric performance of LEDs?

LED chip size can be divided into small power chip, medium power chip and high power chip according to power. According to customer requirements, it can be divided into single tube level, digital level, dot matrix level and decorative lighting. As for the specific size of the chip is based on the actual production level of different chip manufacturers, there is no specific requirements. As long as the process passes, small chips can increase unit output and reduce costs, and the photoelectric performance will not fundamentally change. The current used by the chip is actually related to the current density flowing through the chip. The current used by the chip is small, the current used by the chip is large, and their unit current density is basically the same. Considering that heat dissipation is the main problem under high current, its luminous efficiency is lower than that of small current. On the other hand, as the area increases, the body resistance of the chip will decrease, so the forward voltage will decrease.

LED high-power chips generally refer to what size of chip? Why?

LED high-power chips for white light can generally be seen on the market at around 40mil. The so-called high-power chip power generally refers to electric power above 1W. Since the quantum efficiency is generally less than 20%, most of the electrical energy will be converted into thermal energy, so the heat dissipation of high-power chips is very important, requiring a larger area of the chip.

What are the different requirements of chip technology and processing equipment for manufacturing GaN epitaxial materials compared with GaP, GaAs, InGaAlP? Why?

The substrates of ordinary LED red and yellow chips and high-bright quaternary red and yellow chips all use compound semiconductor materials such as GaP and GaAs, and can generally be made into N-type substrates. A wet process is used for photolithography, and then a diamond blade is used to cut into chips. The blue-green chip of GaN material is a sapphire substrate. Because the sapphire substrate is insulated, it cannot be used as a pole of the LED. Both P / N electrodes must be fabricated on the epitaxial surface by dry etching. There are also some passivation processes. Because sapphire is very hard, it is difficult to divide the chip into diamond chips. Its technological process is generally more and more complicated than GaP, GaAs material LED.

What is the structure and characteristics of the “transparent electrode” chip?

The so-called transparent electrode must first be able to conduct electricity, and the second is to be able to transmit light. This material is now more widely used in the production process of liquid crystals, its name is indium tin oxide, English abbreviation ITO, but it can not be used as a solder pad. During the production process, the ohmic electrode must be made on the surface of the chip, and then the surface is covered with a layer of ITO and then a layer of solder pad is plated on the surface of the ITO. In this way, the current from the lead is evenly distributed to each ohmic contact electrode through the ITO layer. At the same time, because the refractive index of ITO is between the refractive index of air and the epitaxial material, the angle of light can be increased, and the luminous flux can also be increased.

What is the mainstream of chip technology for semiconductor lighting?

With the development of semiconductor LED technology, its application in the field of lighting is also increasing, especially the emergence of white LED, has become a hot spot in semiconductor lighting. However, the key chips and packaging technology still need to be improved. In terms of chips, we must develop towards high power, high light efficiency and lower thermal resistance. Increasing the power means that the current used by the chip is increased. The more direct way is to increase the chip size. The high-power chips that are generally present are around 1mm × 1mm, and the current is 350mA. Due to the increase in the current, the problem of heat dissipation becomes To highlight the problem, the problem is basically solved by the method of chip flipping. With the development of LED technology, its application in the field of lighting will face an unprecedented opportunity and challenge.

What is a “flip chip? What is its structure? What are the advantages?

Blue LEDs usually use Al2O3 substrates, which have high hardness and low thermal and electrical conductivity. If a formal structure is used, on the one hand, it will bring anti-static problems, on the other hand, heat dissipation will become The main problem. At the same time, because the front electrode is facing upward, a part of the light will be blocked, and the luminous efficiency will be reduced. High-power blue LEDs can get more effective light emission than traditional packaging technologies through chip flip-chip technology.

The current mainstream flip-chip structure is: first prepare a large-size blue LED chip with eutectic welding electrodes, and at the same time prepare a silicon substrate that is slightly larger than the blue LED chip, and produce gold for eutectic welding on it Conductive layer and lead wire layer (ultrasonic gold ball solder joint). Then, the eutectic welding equipment is used to weld the high-power blue LED chip and the silicon substrate together.

The characteristic of this structure is that the epitaxial layer is in direct contact with the silicon substrate, and the thermal resistance of the silicon substrate is much lower than that of the sapphire substrate, so the problem of heat dissipation is well solved. Since the sapphire substrate faces upwards and becomes the light emitting surface after flipping, the sapphire is transparent, so the light emitting problem is also solved. The above is the relevant knowledge of LED technology. I believe that with the development of science and technology, the future LED lights will become more and more efficient, and the service life will be greatly improved, bringing us greater convenience.