To understand LED flip chip, we must first understand what is LED chip
LED dress up chip is the earliest appearance of the chip structure, but also the chip structure commonly used in low-power chips. The structure, the electrode in the top, from top to bottom material: P-GaN, light-emitting layer, N-GaN, the substrate. Therefore, the flip is relatively formal dress.
In order to avoid the light-emitting area occupied by the electrode in the packaged chip and thus affect the luminous efficiency, the chip developer designed the flip-chip structure, that is, the packaged chip is inverted and the light excited by the light emitting layer is directly emitted from the other side of the electrode Go, the chip material is transparent), at the same time, designed for flip-chip LED package factory wire structure, thus, the entire chip called flip chip (Flip Chip), the structure is more used in high-power chips.
Dress, flip, vertical LED chip structure of the three genres
Flip technology is not a new technology, in fact, existed long ago. Flip-chip technology is not only used in the LED industry, is also useful in other semiconductor industries. Currently LED chip packaging technology has formed several schools, different technologies correspond to different applications, has its unique features.
The current LED chip structure has three main genres, the most common is the formal structure, as well as vertical structure and flip structure. Due to p, n electrode on the same side of the LED, current crowding tends to occur and the thermal resistance is high. The vertical structure solves both of these problems and achieves high current density and uniformity. The future cost of lighting In addition to the cost of materials, power LED chips to reduce the number seems particularly important, the vertical structure can well meet such needs. This also led to the vertical structure is usually used for high-power LED applications, and formal technology is generally used in small and medium power LED. The flip-chip technology can also be subdivided into two categories, one is based on the sapphire chip flip, sapphire substrate retention, conducive to heat dissipation, but the current density increase is not obvious; the other is the flip-chip structure and stripped the liner Bottom material, can greatly enhance the current density.
The advantages of LED flip chip
First, there is no cooling through the sapphire, through the use of high current; Second, the size can be smaller, easier to match the optical; Third, the cooling function to enhance the life of the chip has been enhanced; Fourth, enhance the anti-static ability; Fifth, lay the foundation for the subsequent packaging process development.
What is LED flip chip
It is understood that the reason why flip-chip is called "flip" is compared with the traditional wire bonding method (Wire Bonding) and after the ball process. Conventional wire bonding through the substrate connected to the wafer with the electrical side up, and flip-chip electrical side down, equivalent to the former flip over, so called "flip chip."
Flip LED chips, GaN-based LED structure layer is grown on the sapphire substrate by MOCVD technology, and the light emitted by the P / N junction luminescent region is emitted through the P-type region above. Due to the poor conductivity of P-type GaN, in order to obtain good current spreading, a layer of Ni-Au metal electrode layer needs to be formed on the surface of P region by evaporation technology. P region leads through the layer of metal film leads. For good current spreading, the Ni-Au metal electrode layer should not be too thin. To this end, the luminous efficiency of the device will be greatly affected, usually both current expansion and output efficiency of two factors. However, no matter under what circumstances, the existence of metal film, will always make the light transmission performance deterioration. In addition, the presence of lead solder joints also affect the light extraction efficiency of the device. The use of GaN LED flip chip structure can fundamentally eliminate the above problems.
Flip chip technology, based on the manufacturers have developed a LED flip chip gold-free chip package.
What is LED flip chip gold-free chip package
Flip gold-free chip-scale package, based on flip-chip technology, based on the traditional LED chip package, reducing the gold wire packaging process, eliminating the lead frame, wire, leaving only the chip with phosphor and plastic packaging . As a new packaging technology products, flip-chip gold-free chip-level light source is completely no due to the gold wire Weld or poor contact caused by not bright, flicker, light fades and other issues. Compared with the traditional packaging process, chip-level light source packaging density increased 16 times, the package volume has shrunk by 80%, lighting design more space. Flip gold-free chip with more stable performance, better heat dissipation, more uniform light color distribution, smaller size, by more and more LED lighting companies and end-product applications of all ages.
LED flip chip popular difficulty:
1, Flip LED technology is currently in high-power products and integrated package has greater advantages in the application of small and medium-power, cost competitiveness is not very strong.
2, Flip LED subverts the traditional LED technology, from the chip until the package, it will require higher equipment, take the package that can do flip-chip front-end equipment costs will certainly increase a lot, which set Threshold, so that some companies simply can not come into contact with this technology.
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