What is an LED chip? So what are its characteristics? The manufacturing of LED chips is mainly aimed at producing effective and reliable low ohmic contact electrodes, which can meet the relatively small voltage drop between contact materials and provide solder pads, while emitting as much light as possible. The film transfer 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 is transformed into metal vapor and deposited on the surface of the semiconductor material under low pressure.
The commonly used P-type contact metals include alloys such as AuBe and AuZn, while the N-side contact metal is often made of AuGeNi alloy. The alloy layer formed after coating also needs to expose the light-emitting area as much as possible through photolithography technology, so that the remaining alloy layer can meet the requirements of effective and reliable low ohmic contact electrodes and solder wire pads. After the photolithography process is completed, an alloying process is also carried out, usually under the protection of H2 or N2. The time and temperature of alloying are usually determined by factors such as the characteristics of semiconductor materials and the form of the alloy furnace. Of course, if the electrode process for blue-green chips is more complex, passivation film growth and plasma etching processes need to be added.

In the manufacturing process of LED chips, which processes have a significant impact on their optoelectronic performance?
Generally speaking, after the completion of LED epitaxial production, its main electrical properties have been finalized, and chip manufacturing does not change its core nature. However, inappropriate conditions during coating and alloying processes can cause some poor electrical parameters. For example, low or high alloying temperatures can cause poor ohmic contact, which is the main reason for high forward voltage drop VF in chip manufacturing. After cutting, performing some corrosion processes on the edges of the chip can be helpful in improving the reverse leakage of the chip. This is because after cutting with a diamond grinding wheel blade, there will be a large amount of debris powder remaining at the edge of the chip. If these particles stick to the PN junction of the LED chip, they will cause electrical leakage and even breakdown. In addition, if the photoresist on the surface of the chip is not peeled off cleanly, it will cause difficulties and virtual soldering of the front solder lines. If it is on the back, it will also cause a high pressure drop. During the chip production process, methods such as surface roughening and cutting into inverted trapezoidal structures can increase light intensity.

Why are LED chips divided into different sizes? What are the effects of size on the photoelectric performance of LED?
The size of LED chips can be divided into low-power chips, medium power chips, and high-power chips according to their power. According to customer requirements, it can be divided into categories such as single tube level, digital level, dot matrix level, and decorative lighting. 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 up to standard, small chips can increase unit output and reduce costs, and the optoelectronic performance will not undergo fundamental changes. The current used by a chip is actually related to the current density flowing through it. A small chip uses less current, while a large chip uses more current. Their unit current density is basically the same. Considering that heat dissipation is the main issue under high current, its luminous efficiency is lower than that under low current. On the other hand, as the area increases, the body resistance of the chip will decrease, resulting in a decrease in the forward conduction voltage.

What is the typical area of LED high-power chips? Why?
LED high-power chips used for white light are generally available in the market at around 40mil, and the power consumption of high-power chips generally refers to electrical power above 1W. Due to the fact that quantum efficiency is generally less than 20%, most electrical energy is converted into heat energy, so the heat dissipation of high-power chips is very important and requires chips to have a large area.

What are the different requirements for the chip process and processing equipment for manufacturing GaN epitaxial materials compared to GaP, GaAs, and InGaAlP? Why?
The substrates of ordinary LED red and yellow chips and high brightness quaternary red and yellow chips are made of compound semiconductor materials such as GaP and GaAs, and can generally be made into N-type substrates. Wet process is used for photolithography, and then diamond grinding wheel blades are used to cut into chips. The blue-green chip made of GaN material uses a sapphire substrate. Due to the insulating nature of the sapphire substrate, it cannot be used as one electrode of the LED. Therefore, both P/N electrodes must be simultaneously fabricated on the epitaxial surface through dry etching process, and some passivation processes must be carried out. Due to the hardness of sapphire, it is difficult to cut it into chips with a diamond grinding wheel blade. Its manufacturing process is generally more complex and intricate than LEDs made of GaP or GaAs materials.

What are the structure and characteristics of the “transparent electrode” chip?
The so-called transparent electrode needs to be conductive and transparent. This material is now widely used in liquid crystal production processes, and its name is indium tin oxide, abbreviated as ITO, but it cannot be used as a solder pad. When making, first make an ohmic electrode on the surface of the chip, then cover the surface with a layer of ITO and plate a layer of solder pad on the ITO surface. In this way, the current coming down from the lead is evenly distributed to each ohmic contact electrode through the ITO layer. At the same time, ITO, due to its refractive index being between that of air and epitaxial materials, can increase the angle of light emission and the luminous flux.

What is the mainstream 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 LED, which has become a hot topic in semiconductor lighting. However, key chip and packaging technologies still need to be improved, and in terms of chips, we need to develop towards high power, high light efficiency, and reduced thermal resistance. Increasing power means an increase in the current used by the chip, and a more direct way is to increase the chip size. The commonly used high-power chips are around 1mm × 1mm, with a current of 350mA. Due to the increase in current usage, heat dissipation has become a prominent problem, and now this problem has been basically solved through the method of chip inversion. With the development of LED technology, its application in the field of lighting will face unprecedented opportunities and challenges.

What is a “flip chip”? What is its structure? What are its advantages?
Blue LED usually uses Al2O3 substrate, which has high hardness, low thermal and electrical conductivity. If a positive structure is used, it will bring anti-static problems on the one hand, and on the other hand, heat dissipation will also become a major issue under high current conditions. Meanwhile, due to the positive electrode facing upwards, a portion of the light will be blocked, resulting in a decrease in luminous efficiency. High power blue LED can achieve more effective light output through chip inversion technology than traditional packaging technology.
The mainstream inverted structure method now is to first prepare large-sized blue LED chips with suitable eutectic soldering electrodes, and at the same time prepare a slightly larger silicon substrate than the blue LED chip, and then make a gold conductive layer and lead out wire layer (ultrasonic gold wire ball solder joint) for eutectic soldering on it. Then, the high-power blue LED chip is soldered to the silicon substrate using eutectic soldering equipment.
The characteristic of this structure is that the epitaxial layer directly contacts 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. Due to the inverted sapphire substrate facing upwards, it becomes the light emitting surface, and sapphire is transparent, thus solving the problem of light emission. The above is the relevant knowledge of LED technology. We believe that with the development of science and technology, future LED lights will become increasingly efficient and their service life will be greatly improved, bringing us greater convenience.