What is an LED chip? So what are its characteristics? LED chip manufacturing is mainly to manufacture effective and reliable low ohm contact electrode, meet the relatively small voltage drop between the contactable materials, provide the pressure pad for the welding wire, and at the same time, as much light as possible. The transition film process generally uses vacuum evaporation method. Under 4Pa high vacuum, the materials are melted by resistance heating or electron beam bombardment heating, and BZX79C18 is turned into metal vapor to deposit on the surface of semiconductor materials under low pressure.

The commonly used P-type contact metals include AuBe, AuZn and other alloys, and the contact metals on the N-side are usually AuGeNi alloys. The alloy layer formed after coating also needs to expose the luminous area as much as possible through photolithography, so that the remaining alloy layer can meet the requirements of effective and reliable low ohm contact electrode and welding line pad. After the photolithography process is completed, the alloying process shall be carried out under the protection of H2 or N2. The time and temperature of alloying 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-green is more complex, the passive film growth and plasma etching process need to be added.

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

Generally speaking, after the completion of LED epitaxial production, its main electrical performance has been finalized. The chip manufacturing will not change its core production nature, but improper conditions in the coating and alloying process will cause some electrical parameters to be poor. For example, low or high alloying temperature will cause poor ohmic contact, which is the main reason for high forward voltage drop VF in chip manufacturing. After cutting, if some etching process is carried out on the chip edge, it will be helpful to improve the reverse leakage of the chip. This is because after cutting with a diamond grinding wheel blade, there will be a lot of debris powder left on the chip edge. If these particles stick to the PN junction of the LED chip, they will cause electric leakage, or even breakdown. In addition, if the photoresist on the chip surface is not peeled off cleanly, it will cause difficulties in front wire bonding and false soldering. If it is the back, it will also cause high pressure drop. In the process of chip production, light intensity can be improved by means of surface roughening and cutting into inverted trapezoid structure.

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

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, lattice level and decorative lighting and other categories. The specific size of the chip depends on the actual production level of different chip manufacturers, and there is no specific requirement. As long as the process is qualified, the chip can improve the unit output and reduce the cost, and the photoelectric performance will not change fundamentally. 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 and the current used by the chip 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 under low current. On the other hand, as the area increases, the volume resistance of the chip will decrease, so the forward conduction voltage will decrease.

What size chip does LED high-power chip generally refer to? Why?

LED high-power chips used for white light can generally be seen in the market at about 40 mils, and the so-called high-power chips generally mean that the electrical power is 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 chips is very important, requiring a larger chip area.

What are the different requirements of chip process 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 quaternary red and yellow chips are made of GaP, GaAs and other compound semiconductor materials, which can generally be made into N-type substrates. The wet process is used for photolithography, and later the diamond wheel blade is used for cutting 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 LED. The P/N electrodes must be made on the epitaxial surface simultaneously through a dry etching process and also through some passivation processes. Because sapphires are very hard, it is difficult to cut chips with diamond grinding wheel blades. Its process is generally more complicated than that of GaP and GaAs LEDs.

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

The so-called transparent electrode should be able to conduct electricity and light. This material is now widely used in liquid crystal production process. Its name is Indium Tin Oxide (ITO), but it cannot be used as a welding pad. During fabrication, the ohmic electrode shall be made on the chip surface, and then a layer of ITO shall be coated on the surface, and then a layer of welding pad shall be coated 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, since the ITO refractive index is between the air and the refractive index of the epitaxial material, the light angle 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 applications in the field of lighting are more and more, especially the emergence of white LED, which has become the focus of semiconductor lighting. However, the key chip and packaging technology still need to be improved, and the chip should be developed towards high power, high luminous efficiency and low thermal resistance. Increasing the power means increasing the current used by the chip. The more direct way is to increase the chip size. Nowadays, high-power chips are all 1mm × 1mm, and the current is 350mA Due to the increase of the use current, the problem of heat dissipation has become a prominent problem. Now this problem has been basically solved by chip flip. With the development of LED technology, its application in the lighting field will face an unprecedented opportunity and challenge.

What is Flip Chip? What is its structure? What are its advantages?

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

The current mainstream flip structure approach is: first, prepare a large size blue LED chip with a suitable eutectic welding electrode, at the same time, prepare a silicon substrate slightly larger than the blue LED chip, and produce a gold conductive layer and lead wire layer (ultrasonic gold wire ball solder joint) for eutectic welding. Then, the high-power blue LED chip and the silicon substrate are welded together using eutectic welding equipment.

This structure is characterized by that the epitaxial layer directly contacts with the silicon substrate, and the thermal resistance of the silicon substrate is far lower than that of the sapphire substrate, so the problem of heat dissipation is well solved. Since the substrate of the sapphire is facing up after inversion, it becomes the light emitting surface. 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, LED lamps in the future will become more and more efficient, and their service life will be greatly improved, bringing us greater convenience.