8 questions which let you to understanding the LED chip

- Nov 20, 2017 -

1 LED chip manufacturing process is what?


LED chip manufacturing is mainly to create effective and reliable low-ohmic contact electrode, and can meet the minimum pressure drop between the contactable materials and pressure pad to provide wire, while as much light as possible. The film-forming process is generally performed by a vacuum evaporation method, mainly melting the material under a high vacuum of 1.33 x 10? 4 Pa by resistance heating or electron beam bombardment heating and turning it into a metal vapor at a low pressure to deposit on the surface of the semiconductor material. Commonly used P-type contact metals include AuBe, AuZn and other alloys, N-side contact metals commonly used AuGeNi alloy. The formed alloy layer also needs to expose the light-emitting region as much 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 bond wire pressure pads. After the photolithography process but also through the alloying process, alloying is usually carried out under the protection of H2 or N2. Alloying time and temperature are usually based on the characteristics of semiconductor materials and alloy furnace form and other factors. Of course, if the blue-green chip electrode process is more complex, need to increase the passivation film growth, plasma etching process.


2 LED chip manufacturing process, which processes have a more important impact on the photoelectric properties?


In general, LED epitaxial production is completed after her main electrical properties have been stereotyped, the manufacture of the chip does not change their nuclear nature, but in the coating, the alloying process of inappropriate conditions can cause some electrical parameters of the poor. For example, low or high alloying temperature will cause ohmic contact failure, ohmic contact is poor manufacturing is caused by the forward voltage drop in the chip is the main reason for the high. After cutting, if the edge of the chip for some etching process, to improve the chip reverse leakage will be better help. This is because the use of diamond wheel blade cutting, the chip edge will remain more debris powder, which if stuck in the LED chip PN junction will cause leakage, and even breakdown phenomenon. In addition, if the chip surface photoresist stripping is not clean, it will cause the front wire is difficult and Weld and so on. If it is the back will cause high pressure drop. In the chip production process through the surface roughening, planted into an inverted trapezoidal structure and other methods can increase the light intensity.


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


LED chip size can be divided according to the power of small power chips, power chips and high-power chips. According to customer requirements can be divided into single-tube level, digital level, lattice level and decorative lighting categories. As for the specific size of the chip is based on the actual production level of different chip manufacturers may not have specific requirements. As long as the craft passes, the small chip can improve the unit output and reduce the cost, and the photoelectric property does not change fundamentally. The current used by the chip is actually related to the current density flowing through the chip. The small current used by the chip and the current used by the large chip are large, and the current density per unit of the chip is basically the same. If the use of 10mil chip current is 20mA, then 40mil chip theoretical current can be increased by 16 times, or 320mA. However, taking into account the heat is a major problem under high current, so its luminous efficiency is lower than the low current. On the other hand, as the area increases, the body resistance of the chip will be reduced, so the forward voltage will be reduced.


4 LED high-power chips generally refers to the size of the chip area? why?


White LED for high-power chips generally available on the market can be seen in about 40mil, the so-called use of high-power chip power generally refers to the electric power in more than 1W. As the quantum efficiency is generally less than 20% most of the electricity will be converted into heat, so the heat dissipation of high-power chips is very important, requires a larger chip area.


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


Ordinary LED red and yellow chips and highlight four yuan red and yellow chip substrate are used GaP, GaAs and other compound semiconductor materials, generally can be made of N-type substrate. Photolithography using a wet process, and finally with a diamond wheel blade cut into chips. The blue-green chip of GaN material is a sapphire substrate. Since the sapphire substrate is insulated, it can not be used as one pole of the LED. Two electrodes of P / N must be simultaneously fabricated on the epitaxial surface by the dry etching process. Pass some passivation process. Because sapphire is hard, it is difficult to draw a chip with a diamond wheel blade. Its process is generally more than GaP, GaAs LED material more and more complex.


6 "transparent electrode" chip structure and what are its characteristics?


The so-called transparent electrode is to be able to conduct electricity, the second is to be able to light. This material is now the most widely used in liquid crystal production process, the name is indium tin oxide, abbreviation ITO, but it can not be used as a pad. First make ohmic electrodes on the surface of the chip when making, and then cover the surface with a layer of ITO and then a layer of pad on the ITO surface. This current from the lead down through the ITO layer evenly distributed to each ohmic contact electrode, while ITO as the refractive index between the air and the refractive index of the epitaxial material, can increase the light angle, the luminous flux can also increase.


7 for the development of semiconductor lighting chip technology what is the mainstream?


With the development of semiconductor LED technology, its application in the field of lighting is also more and more, especially the emergence of white LED, but also become a hot spot in semiconductor lighting. However, the key chip, packaging technology needs to be improved, in the chip to high-power, high luminous efficiency and lower thermal resistance development. Increase the power means that the current use of the chip increases, the most direct way is to increase the chip size, the now common high-power chips are about 1mm × 1mm, the use of current at 350mA. As the use of current increases, the heat problem becomes Prominent problems, and now the chip flip method basically solved this topic. With the development of LED technology, its application in the field of lighting will face an unprecedented opportunity and challenge.


8 what is "flip chip (Flip Chip)"? How is its structure? What are the advantages?


The blue LED usually adopts the Al2O3 substrate. The Al2O3 substrate has high hardness, low thermal conductivity and low conductivity. If the formal structure is adopted, the anti-static problem will be brought about. On the other hand, the heat dissipation will also become The main problem. At the same time as the front electrode up, it will cover part of the light, luminous efficiency will be reduced. High-power blue LED chip flip-chip technology can be more effective than the traditional packaging technology light.


Now the mainstream of flip-chip structure is: first prepared with suitable for eutectic welding electrodes of large-size blue LED chips, while slightly larger than the blue LED chip prepared silicon substrate, and in the above for the eutectic solder gold Conductive layer and the lead wire layer (ultrasonic gold ball solder joints). Then, the use of eutectic welding equipment will be high-power blue LED chip and the silicon substrate welded together. This structure is characterized by direct contact with the silicon substrate epitaxial layer, the thermal resistance of the silicon substrate is far lower than the sapphire substrate, so the heat problem is well solved. As flip-up sapphire substrate up, become a glossy, sapphire is transparent, so the issue of light has also been resolved.