Full-featured phone is ultraslim at 10mm

Recent teardowns by Portelligent—most notably the 10mm-thick UMTS Sony Ericsson W880i—reveal a trimming of the display module waistline to enable a class of highly functional, ultrathin candy-bar cellphones. We go under the glassy surface of the 46mm-diagonal QVGA LCD found in the W880i to highlight some of the methods used to achieve an overall LCD module thickness of just 1.6mm.

Thick and thinner
When the one-year-old Sony Ericsson K800i, also analyzed by Portelligent, is compared with the recently launched W880i, many similarities are found to exist between the phones, including the candy-bar form factor, QVGA display, dual cameras and W-CDMA connectivity. However, the thickness of the devices and their respective display modules couldn't be more different.

At only 10mm, the Sony Ericsson W880i is more than 40 percent thinner than the K800i, even after excluding the additional 5mm camera protrusion found on the K800i. A significant contributor to this reduction in thickness is the svelte QVGA (320 x 240pixel) display module contained in the W880i. Examining the two display modules side by side quickly reveals that the LCD module in the W880i contributes at least 1mm of the 7.6mm profile difference between the phones.

Where is the glass?
When squeezing out an additional 1mm from a 2.6mm-thick display assembly, typically the first component to address would be the glass. At 0.42mm thick, the glass found in the Sony Ericsson W880i display module is one of the thinnest encountered by Portelligent—nearly 59 percent thinner than the glass found in the K800i. The limits of glass durability were quickly discovered when performing additional dissection research for this article, and future reductions in module thickness will likely have to come from other components.

At 0.43mm thick, the main diffuser found in the Sony Ericsson W880i display module now becomes the single thickest layer found in the module, despite trimming off nearly 0.1mm, or 17 percent, in thickness compared with the main diffuser found in the K800i LCD.

Another way of shaving millimeters is to do away with layers and the W880i display module accomplishes that by reducing the number of nonprimary diffusers from two to one. At a thickness of 0.05mm, or half the thickness of a sheet of standard copy paper, the only way to achieve further thickness reductions would be to eliminate the secondary diffuser altogether.

Reflections in the mirror
Moving down the priority list, the two polarizing films found in the W880i measured in at 0.43mm, or 26 percent of the overall module thickness. Surprisingly, the W880i polarizing film measurement was 0.05mm thicker than the two polarizing films found on the K800i. Upon closer examination of one of the W880i polarizing films, a reflective layer was found securely adhered to the surface, so thin that it couldn't be removed during the teardown process. That quasi-elimination of a layer required a comparison of the two polarizing films and two separate reflective layers found in the K800i, vs. the two polarizing films and one separate reflective layer discovered in the W880i.

When the polarizing film and reflective-layer measurements were all tallied, the W880i came out on top with an overall reduction of 0.04mm compared with the K800i. Just as with secondary diffusers, reflective layers, at 0.05mm, are reaching a thickness where little opportunity resides for future reductions unless a layer can be eliminated. However, the polarizing film itself, which has not changed in thickness between module generations and occupies over a quarter of the overall module thickness, certainly presents an area for innovation.

The 10mm-thick UMTS Sony Ericsson W880I enables a class of highly functional, ultrathin candy-bar cellphones. (Click to view teardown.)

The remaining physical layers found in the W880i are two collimators, used to improve the module brightness. The K800i also contained two collimators. All four collimators found in the two devices measured in at 0.06mm, suggesting that with the micro-imprinting used in their manufacture, there is little opportunity for module thickness reductions hiding in the collimation layers.

Two clear films were found in the K800i display module that were not present in the next-generation W880i module. The layers did not appear to have any optical characteristics and thus likely served as protective layers for the LCD module.

The total thickness of the two additional layers found in the K800i module amounted to 0.23mm.

Upon tallying the thickness measurements of the eight discrete layers found in the W880i module, a total of 1.51mm is obtained. Yet the display frame containing all of the layers in a flush arrangement added a further 0.09mm of overall height.

The extra thickness can only be attributed to an approximate 0.01mm of air space and/or adhesive sandwiched between each physical layer. When a similar exercise is performed on the older-generation K800i, the combined physical-layer thickness of 2.3mm vs. the frame thickness of 2.78mm is partially explained by the 10 layers found in the K800i module, but it also indicates a prior unwillingness to have the combined layers mounted flush with the frame.

No plastic backing plate
Not included in the 2.78mm thickness of the K800i module—but an integral part of the display—was a 0.9mm-thick plastic backing plate. Further examination of the K800i component arrangement highlighted the need for this thickness-adding reinforcement: the location of air space directly behind the display module.

The ultrathin W880i does away with this additional space-robbing reinforcement, allowing the battery, which was found to be nestled directly behind the slender display module and an intervening case backing plate, to provide the necessary back-side reinforcement.

The latest-generation cellphone LCD display modules demonstrate a great deal of innovation in reducing the overall thickness to enable a class of full- featured, ultrathin phones. However, further reductions in layer count and thickness like those observed when comparing the Sony Ericsson W880i and K800i will be harder to achieve in the future as required LCD layers reach physical thickness limits.

Announcements by major cellphone manufacturers to incorporate new primary display technologies such as emissive organic OLEDs—which eliminate backlights and reduce optical film count—point to one path for the next wave of ultrathin cellphones. But even OLED modules have a thickness comparable to that of the W880i's trimmed-down LCD. With constant whittling, the LCD incumbent has thus far stayed slim enough to remain the technology of choice.

- Jeff Brown
Principal analyst, Portelligent