What is LED chip? And what are the characteristics? LED chip manufacturing is mainly to manufacture 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. Get as much light out as possible. The film-crossing process generally uses the vacuum evaporation method. Under the high vacuum of 4Pa, the material is melted by resistance heating or electron beam bombardment heating, and the BZX79C18 becomes metal vapor and is deposited on the surface of the semiconductor material under low pressure.

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

In the LED chip manufacturing process, which processes have a more important impact on its optoelectronic properties?

Generally speaking, after the LED epitaxy production is completed, its main electrical properties have been finalized, and the chip manufacturing will not change its core production, but inappropriate conditions during the coating and alloying process will cause some electrical parameters to be bad. For example, if the alloying temperature is too low or too high, it 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, there will be more debris and powder left 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 peeled off cleanly, it will cause difficulties in front-side wire bonding and virtual welding. If it is the back, it will also cause a high voltage drop. In the chip production process, the light intensity can be improved by roughening the surface and dividing it into an inverted trapezoidal structure.

Why are LED chips divided into different sizes? What are the effects of size on the photoelectric performance of LEDs?

The size of LED chips can be divided into low-power chips, medium-power chips and high-power chips according to the power. According to customer requirements, it can be divided into single tube level, digital level, dot matrix level and decorative lighting and other categories. As for the specific size of the chip, it depends on the actual production level of different chip manufacturers, and there are no specific requirements. As long as the process is passed, the small chip can increase the unit output and reduce the cost, and the optoelectronic performance will not fundamentally change. The current used by the chip is actually related to the current density flowing through the chip. The small chip uses a small current, and the large chip uses a large current. Their unit current densities are 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 bulk resistance of the chip will decrease, so the forward voltage will decrease.

LED high-power chip generally refers to what area of ​​chip? Why?

The LED high-power chips used for white light are generally around 40mil in the market. The so-called high-power chips generally use more than 1W of electrical power. Since the quantum efficiency is generally less than 20%, most of the electrical energy will be converted into heat energy, so the heat dissipation of high-power chips is very important, and the chip is required to have a larger area.

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

The substrates of ordinary LED red-yellow chips and high-brightness quaternary red-yellow chips are made of compound semiconductor materials such as GaP and GaAs, which can generally be made into N-type substrates. The wet process is used for photolithography, and then the chips are cut into chips with an emery wheel blade. The blue-green chip of GaN material uses a sapphire substrate. Since the sapphire substrate is insulating, it cannot be used as a pole of the LED. It is necessary to make two P/N electrodes on the epitaxial surface by the dry etching process at the same time. Also through some passivation process. Because sapphire is so hard, it is difficult to chip with a diamond wheel blade. Its process is generally more and more complicated than LEDs made of GaP and GaAs materials.

What is the structure of the "transparent electrode" chip and its characteristics?

The so-called transparent electrode must be able to conduct electricity, and the second is to be able to transmit light. This material is now widely used in the liquid crystal production process, its name is indium tin oxide, the English abbreviation ITO, but it cannot be used as a pad. When making, first make ohmic electrodes on the surface of the chip, then cover the surface with a layer of ITO and then plate a layer of pads 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, since the refractive index of ITO is between the refractive index of air and the epitaxial material, the light output angle can be increased, and the luminous flux can also be increased.

What is the mainstream of the development 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 LEDs, which has become a hot spot in semiconductor lighting. However, the key chip and packaging technologies still need to be improved. In terms of chips, it is necessary to develop towards high power, high light efficiency and lower thermal resistance. Increasing the power means that the current used by the chip increases. The more direct way is to increase the size of the chip. Now the common high-power chips are about 1mm × 1mm, and the current is 350mA. Due to the increase in the current, the problem of heat dissipation has become The outstanding problem is now basically solved by the method of flip chip. With the development of LED technology, its application in the field of lighting will face unprecedented opportunities and challenges.

What is "flip chip? What is its structure? What are the advantages?

Blue LEDs usually use Al2O3 substrates. Al2O3 substrates have high hardness and low thermal conductivity and electrical conductivity. If a positive structure is used, on the one hand, it will bring anti-static problems. more important issue. At the same time, since the front electrode faces upward, part of the light will be blocked, and the luminous efficiency will be reduced. High-power blue LEDs can obtain more effective light output through flip-chip technology than traditional packaging technology.

The current mainstream flip-chip structure method is to first prepare a large-size blue LED chip with electrodes suitable for eutectic welding, and at the same time prepare a silicon substrate slightly larger than that of the blue LED chip, and fabricate gold for eutectic welding on it. Conductive layer and lead wire layer (ultrasonic gold wire ball bonding point). Then, the high-power blue LED chip and the silicon substrate are welded together using eutectic welding equipment.

The feature 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 up after flip-chipping, it becomes the light-emitting surface, and the sapphire is transparent, so the problem of light-emitting 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.