Design and Technology Trends of LED NB panels

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The use of LEDs for the backlight’s light source has created new business opportunities in the maturing NB panel market. In contrast to CCFLs, white LEDs provide higher color saturation and are mercury-free and less power-consuming–making them more environmentally friendly.  

 

In addition, they enable panels to be designed slimmer. The major panel makers will all be emphasizing on their respective launches of new LED backlit NB panels in 2H08. AUO appears to be the most aggressive, where it stated all of its NB panels will employ LEDs by 2011. Meanwhile, in the end product segment, Apple made a huge impression on people with its Macbook Air, a mere 0.4mm thick LED backlit NB. Given the support from the up-, mid- and downstream industries, the LED NB market penetration rate is projected to reach 15% in 2008. Long-term speaking, the future prospects are even more promising.

 

Nevertheless, despite the LEDs’ inherent advantages, the main obstacle to widespread adoption arises from the high manufacturing and material costs. Thus, in addition to the introduction of lighter and thinner high-end LED backlights, the development of inexpensive entry-level versions has made inroads, as well.

 

 

Backlight categorized by type of light guide plate

 

Whether the LED backlight can be made thin relies on the type of light guide plate used. By looking at the current mainstream designs, the light guide plate is basically classified as flat or wedge-shaped. The latter is thicker, and the design concept is also found in CCFL backlights. Meanwhile, based on the surface structure, the panel itself can be categorized as the V-cut or Dot type.

 

The thickness of the V-cut and Dot type are similar, ranging between 0.7~1.1 mm for varying panel sizes. The main difference between the two lies in the brightness enhancement efficiency, where the V-cut outperforms the other. Although the light guide plate of the two is formed via a high-speed injection process, the V-cut’s up-side-down V shaped structure is harder to form. In the subsequent backlight assembly, problems such as scratches are easily created. Thus, the current yield rate is still below 50%, resulting in higher costs and hampering interested players from adopting the technology. Separately, although the current yield rate of the Dot type light guide plate is not high either, given the relatively simple surface structure, there is room for additional improvements. In recent years, several backlight unit manufacturers have invested in high-speed injection molding equipment in further developing and improving the technology.

 

In order to rapidly reduce the LED backlight costs, the use of wedge type light guides have gradually risen. The thickness ranges between 0.6~2.5mm, not much better than the 0.8~2..0 mm for CCFLs. However, without adopting the high-speed injection process, the yield rate reaches a whopping 90%, significantly cutting down costs and boosting the market penetration.

 

 

Inner design of the LED differs greatly

 

In the ongoing development of LED backlights, the inner design can vary significantly. For high-end LED backlights, which emphasize on the 「slim design」, it requires the usage of side-view LEDs. As such products are mainly the domain of Japanese LED manufacturers; they entail a higher price tag. In contrast to the entry-level models, the thicker top- view LED is employed, where Taiwan makers are capable of producing. Amid the intense market competition, the latter enjoys more price flexibility.

 

Functioning as the backlight’s light source, the side emitting LED and CCFL design are similar, appearing as an elongated-shaped light bar. For the mounting board, based on the thickness, it can be categorized as the traditional PCB or more expensive but thinner FPC.

 

 

Backlight design accommodates panel component layout

 

In the optical film design, there are minimal differences between the CCFL and LED. In general, a brightness enhancement film is employed together with an upper diffuser film. For the special V-cut backlight, a special film can also be added, thereby boosting the brightness efficiency by 15~30%. Unfortunately, due to the high costs, there have been few adopters.

 

For the power supply, the LED requires a converter and a LED driver chip, while CCFLs use a transformer and an inverter.

 

Aside from the backlight itself, the glass substrate is also designed differently for LED panels. To accommodate the slim design of LED backlights, the glass substrates thickness need to be further reduced from 0.5mm to 0.3mm for the 12.1W and 13.3W NB, which emphasize on the mobility niche market.

 

Figure: Comparison of NB BLU Design

 

 

Wedge type more competitive in the initial stage

Long term speaking flat-type expected to gain upper hand

 

The adoption of LEDs in NB panels is expected to gradually increase. In the initial phase, despite the wedge type’s inability to make the panel thinner, its lower cost advantage still makes it suitable for adoption in 14.1W and 15.4W NBs, thus increasing the overall LED NB penetration rate. To truly make LED NB panels thinner and lighter, the DOT type is the more viable candidate. Currently, due to lower yield rate and higher material costs, it is only being adopted in the smaller sized segment, namely the 12.1W and 13.3W. Yet, long term speaking, as the yield rate is expected to improve, it should gradually gain traction in becoming the new mainstream design for NB LEDs. As for the V-cut approach, given the persisting low yield rates, the overly high costs will make it gradually fade away from the market.  

 

From Witsview, a subsidiary of DRAMeXchange Tech Inc.