360-degree analysis of LED flip chip knowledge

What is LED flip chip? In recent years, flip chip technology has been emerging in the field of chips, especially in the high-power and outdoor lighting application market. However, due to its late development, many people do not know what LED flip chip is and what are the advantages of LED flip chip? Today, the editor of Huicong LED Screen Network will give you a simple explanation. First, we will explain LED flip chip to you from the perspective of LED flip chip, as well as the advantages and difficulties of LED flip chip popularization.

　　To understand LED flip chips, you must first understand what LED front chips are.

　　LED upright chip is the earliest chip structure and is also the most commonly used chip structure in low-power chips. In this structure, the electrode is on the top, and the materials from top to bottom are: P-GaN, light-emitting layer, N-GaN, substrate. Therefore, it is upright compared to flip chip.

LED flip chip and symptom chip diagram

　　In order to avoid the situation in which the electrodes in upright chips occupy the light-emitting area and thus affect the light-emitting efficiency, chip developers designed a flip-chip structure, that is, turning the upright chip upside down so that the light excited by the light-emitting layer is emitted directly from the other side of the electrode (the substrate is eventually peeled off and the chip material is transparent). At the same time, a structure is designed for flip-chip that is convenient for LED packaging factories to weld wires. Thus, the entire chip is called a flip chip. This structure is mostly used in high-power chips.

　　Three major schools of LED chip structure : front mount, flip-chip, and vertical 

　　Flip-chip technology is not a new technology, in fact, it has existed for a long time. Flip-chip technology is not only used in the LED industry, but also in other semiconductor industries. At present, LED chip packaging technology has formed several schools, and different technologies correspond to different applications, each with its own unique features.

　　At present, there are three main schools of thought in LED chip structure. The most common one is the upright structure, and there are also vertical structure and flip-chip structure. The upright structure is prone to current crowding due to the p and n electrodes on the same side of the LED, and the thermal resistance is high. The vertical structure can solve these two problems very well, and can achieve very high current density and uniformity. In the future, in addition to material costs, it is particularly important to reduce the power and reduce the number of LEDs to reduce the cost of lamps. The vertical structure can meet such needs very well. This also leads to the vertical structure being usually used in high-power LED applications, while the upright technology is generally used in small and medium-power LEDs. The flip-chip technology can also be divided into two categories. One is flip-chip on the basis of sapphire chips. The sapphire substrate is retained, which is conducive to heat dissipation, but the current density is not significantly improved; the other is the flip-chip structure and the substrate material is stripped off, which can greatly increase the current density.

　　Advantages of LED flip chip

　　First, since heat is not dissipated through sapphire, it can be used with large currents; second, the size can be made smaller, making optical matching easier; third, the improved heat dissipation function increases the life of the chip; fourth, the anti-static ability is improved; and fifth, it lays the foundation for the subsequent development of packaging technology.

　　What is LED flip chip

　　It is understood that the reason why the flip chip is called "flip chip" is relative to the traditional metal wire bonding connection method (Wire Bonding) and the process after ball implantation. The traditional chip connected to the substrate through metal wire bonding has the electrical surface facing up, while the electrical surface of the flip chip faces down, which is equivalent to turning the former over, so it is called "flip chip".

　　The flip-chip LED chip uses MOCVD technology to grow a GaN-based LED structure layer on a sapphire substrate, and the light emitted by the P/N junction light-emitting area is emitted through the P-type area above. Due to the poor conductivity of P-type GaN, in order to obtain good current expansion, it is necessary to form a metal electrode layer composed of Ni-Au on the surface of the P area through evaporation technology. The P area lead is led out through this layer of metal film. In order to obtain good current expansion, the Ni-Au metal electrode layer cannot be too thin. For this reason, the luminous efficiency of the device will be greatly affected, and usually both current expansion and light extraction efficiency must be considered at the same time. However, no matter what the circumstances, the presence of the metal film will always make the light transmission performance worse. In addition, the presence of the lead solder joints also affects the light extraction efficiency of the device. The use of the GaN LED flip chip structure can fundamentally eliminate the above problems.

　　Based on the flip chip technology, some manufacturers have developed LED flip chip-level packaging without gold wire.

　　What is LED flip chip packaging without gold wire

　　Flip-chip gold-wire-free chip-level packaging is based on flip-chip soldering technology. On the basis of traditional LED chip packaging, it reduces the gold wire packaging process, saves lead frames and wire bonding, and only leaves the chip with phosphor and packaging glue. As a new packaging technology product, the flip-chip gold-wire-free chip-level light source has no problems such as dimming, flickering, and high light decay caused by poor soldering or contact of gold wires. Compared with traditional packaging processes, the packaging density of chip-level light sources has increased by 16 times, while the packaging volume has decreased by 80%, leaving more room for lamp design. Flip-chip gold-wire-free chips are favored by more and more LED lighting companies and terminal product application companies due to their more stable performance, better heat dissipation, more uniform light color distribution, and smaller size.

　　Difficulties in popularizing LED flip chips:

　　1. Flip-chip LED technology currently has greater advantages in high-power products and integrated packaging, but its cost competitiveness is not very strong in small and medium-power applications.

　　2. Flip-chip LED has overturned the traditional LED process, from chip to packaging, which will place higher requirements on equipment. Take packaging as an example. The cost of front-end equipment capable of flip-chip will definitely increase a lot. This sets a threshold, making it impossible for some companies to access this technology.

　　LED flip chip manufacturers recommend:

　　As the only leading brand of high-power LED integrated chips in China that has maturely applied flip-chip technology, Jinko Electronics launched a "chip-level LED lighting overall solution" this year. It can complete part of the traditional packaging process or save traditional packaging process links in the LED chip manufacturing process through new wafer-level processes, making the final LED packaging volume smaller and the performance more stable. Its "Easy Series" and ceramic-based COB products all use APT patented technology - flip-chip welding technology, which realizes gold wire-free and solid-crystal glue-free packaging of single-chip and multi-chip modules, and has many advantages such as high brightness, high light efficiency, high reliability, low thermal resistance, and good color consistency.

　　E-HORA's "Northern Lights" 1A LED lighting -level high-drive current flip chip can achieve 310 lumens under 1A current drive, and 255 lumens under 700ma current drive. In addition to high single-point luminous flux, it is suitable for light distribution design and interprets lighting art; comfortable light color quality, professionally designed for high-quality lighting environment; it also has customer-satisfactory light efficiency performance and cost performance; industry-leading thermal performance; reflow soldering process (IPC/JEDEC J-STD-020C); moisture sensitivity level 1; static voltage resistance 8000V (human body mode). Flip chips can be widely used in LCD backlights, high-power LED lighting products, such as street lights, car lights, etc.

　　As one of the domestic LED chip manufacturers, HC Semitek has accumulated considerable experience in the research and development of white light LEDs and formed independent intellectual property rights. It has also conducted in-depth and detailed research on the process of flip-chip LEDs, and continuously improved epitaxy and chip process technology. At present, the test brightness of the 45mil flip-chip product is @1A, 100lm/W, reaching the domestic leading level. HC Semitek's professional R&D team is committed to the research and development of flip-chip LED chips, and has successfully developed them, and will eventually realize the industrialization of flip-chip LED chip products.