Technology

Interpretation of LED chip

1, what is the manufacturing process of LED chip?

The LED chip is designed to produce an effective and reliable low ohm contact electrode, and to meet the minimum pressure drop between the contact materials and the cushion for providing welding lines, and as much as possible. The vacuum coating process is usually applied to the membrane process, mainly in 1.33 * 10? Under high vacuum, 4Pa melts the material with resistance heating or electron beam bombardment, and then changes to vapor vapor at low pressure to deposit on the surface of semiconductor material. The commonly used P type contact metals include AuBe, AuZn and other alloys. The contact metal on the N surface often adopts AuGeNi alloy. The alloy layer formed after the coating also needs to be exposed as much as possible through the photolithography process, so that the left alloy layer can meet the requirements of the effective and reliable low ohm contact electrode and welding wire pad. After the photolithography process is finished, alloying is also needed, and alloying is usually carried out under the protection of H2 or N2. Alloying time and temperature are usually determined by factors such as semiconductor material characteristics and alloy furnace form. Of course, if the green and green chip electrode technology is complex, we need to increase passivation film growth and plasma etching process.

2, which processes affect the photoelectric properties of LED chip manufacturing process?

In general, after the completion of the LED epitaxial production, her main electrical properties have been fixed, and the chip manufacturing does not change its nuclear nature, but the improper conditions in the process of coating and alloying will cause some bad electrical parameters. For example, the low or high alloying temperature will cause the poor ohm contact, and the poor ohm contact is the main reason for the high VF of the forward pressure drop in the chip manufacturing. After cutting, if there are some etching processes on the chip edge, it will help to improve the reverse leakage of the chip. This is because the chip edge will remain more debris after cutting with a diamond wheel blade, which will cause leakage and even breakdown if it is stuck at the PN junction of the LED chip. In addition, if the surface of the chip lithography stripping is not clean, will cause positive and difficult to weld welding line etc.. If it is on the back, the pressure drop will be high. By surface roughening, into inverted trapezoid structure and other measures in the manufacturing process can improve the light intensity.

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

The size of LED chip can be divided into small power chip, middle 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 category. The specific size of chips is determined according to the actual production level of different chip manufacturers, and there is no specific requirement. As long as the process pass, can improve the chip unit output and reduce the cost, and will not fundamentally change the photoelectric properties. The use current of the chip is actually related to the current density of the chip, the small use current of the chip and the large current of the chip are large, and the unit current density is almost almost the same. If the current of the 10mil chip is 20mA, then the 40mil chip can theoretically increase the current by 16 times, that is, 320mA. But considering the heat dissipation is the main problem under high current, its luminous efficiency is lower than that of low current. On the other hand, due to the increase of the area, the body resistance of the chip will decrease, so the forward conduction voltage will decrease.

4, LED, high-power chip generally refers to the large area of the chip? Why?

The LED high power chip used in white light is generally seen in the market around 40mil. The power of the so-called high power chip usually refers to the power of more than 1W. Because the quantum efficiency is generally less than 20%, most of the electric energy will be converted to thermal energy, so the heat dissipation of the high-power chip is very important, which requires that the chip has a larger area.

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

The common LED red and yellow chips and the high brightness four yuan red yellow chip substrates are made of GaP, GaAs and other compound semiconductor materials, which can usually be made into N type substrates. The wet process is used for photolithography, and finally the chip is cut by emery wheel blade. The blue and green chip of the GaN material is a sapphire substrate. Because the sapphire substrate is insulated, it can not be used as a pole of the LED. It is necessary to make the two electrodes on the epitaxial surface at the same time through the dry etching process and also have a few passivation processes. Because the sapphire is very hard, it is difficult to use emery wheel blade into chip. Its technological process is usually more complex than that of GaP and GaAs LED.

6, what is the structure and characteristics of transparent electrode chip?

The so-called transparent electrode is conductive, and the two is transparent. This material is most widely used in liquid crystal production process now. Its name is indium tin oxide, abbreviation ITO, but it can’t be used as welding pad. To make the ohmic electrode on the surface of the chip, then make a layer of ITO on the surface and deposit a pad on the surface of the ITO. The current from the lead is distributed evenly over the ITO layer to the various ohmic contact electrodes. At the same time, the ITO can increase the light angle and increase the luminous flux because the refractive index is between the refractive index of the air and the epitaxial material.

7, 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 is becoming the focus of semiconductor lighting. But the key chip and packaging technology needs to be improved, and it will develop towards high power, high efficiency and low thermal resistance. Increasing the power means that the use current of the chip is increased, the most direct way is to increase the size of the chip. Now the widespread high-power chips are around 1mm * 1mm. The use of current in 350mA. because of the increase of the use of current, heat dissipation becomes a prominent problem. Now the method of chip inversion is basically solved this problem. With the development of LED technology, its application in the lighting field will face an unprecedented opportunity and challenge.

8. What is “Flip Chip”? What is the structure of it? What are the advantages?

The blue light LED usually uses the Al2O3 substrate. The hardness of the Al2O3 substrate is very high, the thermal conductivity and the conductivity are low. If the positive structure is used, the anti static problem will be brought about on the one hand. On the other hand, the heat dissipation will be the most important problem in the case of large current. At the same time as the positive electrode is upward, will hide a portion of the light, the luminous efficiency will decrease. High power blue LED can get more effective light emission than traditional packaging technology through chip flip chip technology.

The mainstream inversion structure method is: first, a large size blue LED chip with a eutectic welding electrode is prepared, and the silicon substrate which is slightly larger than the blue light LED chip is prepared, and the gold conductive layer and lead wire layer (ultrasonic wire solder joint) for eutectic welding are made on it. Then, the high power blue LED chip is welded to the silicon substrate by eutectic welding equipment. The characteristic of this structure is that the epitaxial layer is directly connected with the silicon substrate, and the thermal resistance of the silicon substrate is much lower than the sapphire substrate, so the heat dissipation problem is well solved. Due to the upside down of sapphire substrate, the sapphire is transparent, so the problem of light emission is also solved.

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