What is led chip? So what are its characteristics? LED chip manufacturing is mainly to manufacture effective and reliable low ohmic contact electrodes, meet the relatively small voltage drop between contactable materials, provide pressure pads for welding wires, and emit light as much 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 and deposited on the surface of semiconductor material under low pressure.

Generally, the p-type contact metal used includes Aube, auzn and other alloys, and the n-side contact metal often adopts AuGeNi alloy. The contact layer of the electrode and the exposed alloy layer can effectively meet the requirements of the lithography process. After the photolithography process, it is also through the alloying process, which is usually carried out under the protection of H2 or N2. The alloying time and temperature are usually determined according to the characteristics of semiconductor materials and the form of alloy furnace. Of course, if the chip electrode process such as blue and green is more complex, passive film growth and plasma etching process need to be added.

In the manufacturing process of LED chip, which process has an important impact on its photoelectric performance?

Generally speaking, after the completion of LED epitaxial production, its main electrical properties have been finalized, and the chip manufacturing will not change its nuclear nature, but improper conditions in the process of coating and alloying will cause some adverse electrical parameters. For example, low or high alloying temperature will cause poor ohmic contact, which is the main reason for the high forward voltage drop VF in chip manufacturing. After cutting, if some corrosion processes are carried out on the edge of the chip, it will be helpful to improve the reverse leakage of the chip. This is because after cutting with a diamond grinding wheel blade, more debris and powder will remain at the edge of the chip. If these are stuck to the PN junction of the LED chip, they will cause electric leakage and even breakdown. In addition, if the photoresist on the chip surface is not stripped clean, it will cause difficulties in front welding and false welding. If it is on the back, it will also cause high pressure drop. In the process of chip production, the light intensity can be improved by coarsening the surface and dividing it into inverted trapezoidal structure.

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

LED chip size can be divided into low-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, it is determined according to the actual production level of different chip manufacturers, and there is no specific requirement. As long as the process passes, the chip can improve the unit output and reduce the cost, and the photoelectric performance will not change fundamentally. The use current of the chip is actually related to the current density flowing through the chip. When the chip is small, the use current is small, and when the chip is large, the use current is large. 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 low current. On the other hand, as the area increases, the body resistance of the chip will decrease, so the forward on voltage will decrease.

What is the area of LED high-power chip? Why?

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

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

The substrates of ordinary LED red and yellow chips and bright Quad red and 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 lithography, and then the diamond grinding wheel blade is used to cut the chip. The blue-green chip of GaN material is a sapphire substrate. Because the sapphire substrate is insulated, it can not be used as one pole of LED. It is necessary to make p / N electrodes on the epitaxial surface at the same time through dry etching process, and some passivation processes. Because sapphire is very hard, it is difficult to draw chips with diamond grinding wheel blade. Its technological process is generally more and complex than that of LED made of gap and GaAs materials.

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

The so-called transparent electrode should be conductive and transparent. This material is now widely used in the liquid crystal production process. Its name is indium tin oxide, which is abbreviated as ITO, but it can not be used as a solder pad. During fabrication, ohmic electrode shall be made on the surface of the chip, then a layer of ITO shall be covered on the surface, and then a layer of welding pad shall be plated on the ITO surface. 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 epitaxial material, the light angle can be improved and the luminous flux can 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 more and more, especially the emergence of white LED has become a hot spot of semiconductor lighting. However, the key chip and packaging technology need to be improved. In terms of chip, we should develop towards high power, high luminous efficiency and reducing thermal resistance. Increasing the power means that the use current of the chip is increased. The more direct way is to increase the chip size. Now the common high-power chips are 1mm × 1mm or so, and the operating current is 350mA Due to the increase of the use current, the heat dissipation problem has become a prominent problem. Now this problem is basically solved by the method of chip flip. With the development of LED technology, its application in the field of lighting will face an unprecedented opportunity and challenge.

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

Blue LED usually adopts Al2O3 substrate. Al2O3 substrate has high hardness and low thermal conductivity. If it adopts formal structure, on the one hand, it will bring anti-static problems; on the other hand, heat dissipation will also become a major problem under high current. At the same time, because the front electrode is upward, some light will be blocked, and the luminous efficiency will be reduced. High power blue LED can get more effective light output through chip flip chip technology than traditional packaging technology.

At present, the mainstream flip chip structure method is: first, prepare a large-size blue LED chip with eutectic welding electrode, prepare a silicon substrate slightly larger than the blue LED chip, and make a gold conductive layer and lead out wire layer (ultrasonic gold wire ball solder joint) for eutectic welding on it. Then, the high-power blue LED chip and silicon substrate are welded together by eutectic welding equipment.

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. Because the sapphire substrate faces upward after flip mounting, it becomes a light emitting surface, and 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 lamps will be more and more efficient, and the service life will be greatly improved, which will bring us greater convenience.