Analyze high-power white LED applications and heat dissipation of LED chips

Although it seems to be quite good in terms of features, there are actually some shortcomings, just like the service life is only about 3,000 hours, and the price is too expensive, it is not easy to solve things, maybe the price is too expensive. The problem can be reduced in a little while, but at the current level of 300,000 yen, it will take more than 10 years to fall to 3,000 or even 300 yen.

As far as today is concerned, white LEDs still have poor uniformity of illumination, and the life of the sealing materials is not long, and the application advantages of white LEDs cannot be exerted. However, as far as the demand level is concerned, not only the general lighting use, but also the widespread application of mobile phones, LCD TVs, automobiles, medical treatments, etc., the technical research results that are most suitable for developing stable white LEDs are quite concerned.

Increase the amount of luminescence by increasing the area of ​​the wafer

It is expected to improve the luminous efficiency of white LEDs. Currently, there are two major directions, namely, to increase the area of ​​LED chips. That is to say, the current small area of ​​1 mm2 wafers will increase the light-emitting area to more than 10 mm2, thereby increasing the amount of light. Or package several small chips together under the same module.

Although the area of ​​the LED chip is increased in size, it is possible to obtain a high degree of brightness, but due to an excessive area, there is a counterproductive phenomenon in the application process and results. Therefore, in response to such problems, some LED manufacturers have improved the surface of the wafer according to the improvement of the electrode structure and the flip chip structure to achieve a luminous efficiency of 50 lm/W.

For example, in the portion of the white LED flip chip package, since the light emitting layer is very close to the vicinity of the package, the light of the light emitting layer is scattered to the outside, so the electrode is not shielded, but the disadvantage is that the generated heat is not easily dissipated.

Instead of improving the surface of the wafer, and increasing the area of ​​the wafer, the brightness can be increased in one breath, because when the light is scattered outward from the inside of the wafer, the improved portion of the wafer cannot be reflected, so it is subject to light extraction. A little limitation, according to the calculation, the LED chip size that best utilizes light efficiency is about 7mm2.

Quickly increase luminous efficiency by encapsulating several small-area LED chips

Compared with large-area LED chips, low-power LED chips are packaged into the same module, which is capable of achieving high brightness quickly. For example, Citizen packages 8 small LEDs together to make the module's luminous efficiency. It reached 60lm/W, which is the first in the industry.

However, this kind of practice also raises some doubts, because many LEDs are packaged on the same module, so some insulating materials must be placed in the module to avoid short circuit between LED chips, but such a It will add a lot of cost.

Citizen's explanation is that the impact on cost is actually quite small, because these insulation materials are less than one percent compared to the overall cost ratio, and can be insulated by using existing materials. Applications, these insulation materials do not need to be redeveloped, and there is no need to add new equipment to respond.

Although Citizen's interpretation is theoretically reasonable, it is a challenge for less experienced companies because it needs to be overcome in terms of yield, R&D, and production engineering.

Of course, there are other ways to achieve the goal of improving luminous efficiency. Many companies have found that making uneven structures on LED sapphire substrates may increase the light output, so gradually develop texture on the surface of the wafer or Photonics crystallized architecture.

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