Eight questions and answers comprehensive decryption LED chip knowledge

- Jun 01, 2017-

1, LED chip manufacturing process is what?

LED chip manufacturing is mainly to create an effective and reliable low ohmic contact electrode, and can meet the minimum pressure drop between the contactable material and provide pressure pad pressure, while as much as possible to light. Filtration process is generally vacuum deposition method, which is mainly in the 1.33 × 10? 4Pa high vacuum, with resistance heating or electron beam bombardment heating method to melt the material, and in low pressure into a metal vapor deposition in the semiconductor material surface. Generally used P-type contact metal, including AuBe, AuZn and other alloys, N surface contact metal often used AuGeNi alloy. The alloy layer formed after coating also needs to expose the light emitting area 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 electrode and bond pad. After the end of the photolithography process through the alloying process, alloying is usually carried out under the protection of H2 or N2. The time and temperature of the alloying are usually determined by factors such as the characteristics of the semiconductor material and the form of the alloy furnace. Of course, if the blue and green chip electrode process but also complex, need to increase the passive film growth, plasma etching process.

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

In general, after the completion of LED epitaxial production of her main electrical properties have been stereotypes, chip manufacturing does not change its nuclear properties, but in the coating, alloying process inappropriate conditions will cause some electrical parameters of the bad. For example, alloying temperature is low or high will cause poor ohmic contact, ohmic contact is caused by chip manufacturing voltage drop VF high main reason. After cutting, if the edge of the chip for some corrosion process, to improve the chip's reverse leakage will be a better help. This is because with the diamond wheel blade cutting, the edge of the chip will leave more debris powder, which if the LED chip in the PN junction will cause leakage, and even there will be breakdown phenomenon. In addition, if the chip surface photoresist stripping is not clean, will cause the front line is difficult and Weld and so on. If it is on the back will cause a high pressure drop. In the chip production process through the surface rough, into a trapezoidal structure and other ways to improve the light intensity.

3, LED chip why should be divided into such as 8mil, 9mil, ..., 13 ∽ 22mil, 40mil and other different sizes? Size of the LED photoelectric performance What are the impact?

LED chip size according to the power can be divided into low-power chip, the power chip and high-power chip. According to customer requirements can be divided into single-tube, digital, dot matrix and decorative lighting and other categories. As for the specific size of the chip size is based on the actual production level of different chip manufacturers may be, no specific requirements. As long as the process clearance, chip can increase the unit output and reduce costs, photoelectric performance and will not fundamentally change. The current use of the chip is actually related to the current density flowing through the chip, the chip is small, the current is small, the chip is large, and their current density is almost the same. If the 10mil chip using the current is 20mA, then the 40mil chip theoretically use the current can be increased by 16 times, or 320mA. But taking into account the heat is the main problem under high current, so its luminous efficiency is lower than the small current. On the other hand, due to the increase in area, the chip's body resistance will be reduced, so the forward conduction voltage will be reduced.

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

For the white LED high-power chip is generally seen in the market are about 40mil, the so-called high-power chip power is generally used in more than 1W power. As the quantum efficiency is generally less than 20? Most of the energy will be converted into heat, so the power of high-power chip is very important, requiring a larger area of the chip.

5, the manufacture of GaN epitaxial materials, chip processing and processing equipment and GaP, GaAs, InGaAlP compared to what different requirements? Why?

Ordinary LED red and yellow chips and bright four-element red and yellow chip substrates are GaP, GaAs and other compound semiconductor materials, generally can be made of N-type substrate. Using wet process for lithography, and finally cut into chips with diamond blades. GaN material is a sapphire substrate, because the sapphire substrate is insulated, it can not be used as a pole of the LED, must be through the dry etching process on the epitaxial surface at the same time the preparation of P / N two electrodes and But also through some passivation process. As sapphire is very hard, with diamond blade is difficult to cut into chips. Its process is generally more than GaP, GaAs material LED and more complex.

6, "transparent electrode" chip structure and what is its characteristics?

The so-called transparent electrode one is to be able to conduct electricity, the second is to be able to light. This material is now most widely used in liquid crystal production process, its name is indium tin oxide, the English abbreviation ITO, but it can not be used as a pad. Production should be done in the chip surface ohm electrode, and then cover the surface of a layer of ITO ITO surface in a layer of pad. So that the current from the lead down through the ITO layer evenly distributed to the various ohmic contact electrodes, while ITO due to the refractive index in the air and the refractive index between the epitaxial material, can increase the light angle, luminous flux can also increase.

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

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, is a hot spot for semiconductor lighting. But the key chip, packaging technology has yet to be improved, in the chip to high power, high luminous efficiency and reduce thermal resistance development. Improve the power means that the use of the chip to increase the current, the most direct way is to increase the chip size, and now the emergence of high-power chips are 1mm × 1mm or so, the use of current at 350mA. As the use of electric current increases, heat problems become prominent problems, and now through 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 challenges.

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

Blue LED is usually used Al2O3 substrate, Al2O3 substrate hardness is high, thermal conductivity and conductivity is low, if the use of formal structure, on the one hand will bring anti-static problem, on the other hand, in the case of high current heat will become The most important question. At the same time as the front electrode up, will cover up part of the light, luminous efficiency will be reduced. High-power blue LED through chip flip technology can be more than the traditional packaging technology to get more effective light.

Now the mainstream flip-chip structure is: first prepared with eutectic welding electrodes for large-size blue LED chip, while preparing a slightly larger than the blue LED chip silicon substrate, and in the above made for the eutectic welding gold Conductive layer and lead wire layer (ultrasonic gold ball solder joints). The high power blue LED chip is then soldered to the silicon substrate using a eutectic welding device. This structure is characterized by the epitaxial layer directly contact with the silicon substrate, silicon substrate thermal resistance is far lower than the sapphire substrate, so the heat problem is solved. As the sapphire substrate after the flip up, become a smooth, sapphire is transparent, so the light problem has been resolved.


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