[CEATEC] How Did Toshiba Realize World's Slimmest, Lightest Notebook PC?
Toshiba Corp showcased the "dynabook R631," the world's slimmest, lightest 13.3-inch notebook computer, at CEATEC Japan 2011, which took place from Oct 4 to 8, 2011, in Chiba Prefecture, Japan.
The company also exhibited see-through and disassembled models to introduce its technologies used for reducing the thickness and weight of the notebook.
The thickness of the dynabook R631 (excluding protrusions) is 15.9mm, and its mass is about 1.12kg. The slimness and light weight were realized by using techniques to mount components in a high density and improve the robustness of a thin chassis.
The display part of the notebook is about 4.5mm thick. And the other part (on the side the keyboard) has a 11mm-thick space for components to be mounted. Because it was difficult to place a printed circuit board (PCB) over or below a lithium-ion (Li-ion) battery, Toshiba placed a PCB under the keyboard and a Li-ion battery using prismatic cells, which contribute to reducing thickness, under the palm rest.
The capacity of the battery is 47Wh though it is lower than that of the company's notebook PC with a long battery life (67Wh). To reduce the size of the PCB and place it in a limited space, Toshiba mounted components in a high density by arranging small, low-height components on the both sides of the PCB.
To reduce the thickness of a notebook PC, it is necessary to improve resistance to twist. For example, some users hold a notebook PC by gripping a front corner of its lower chassis (on the side of the keyboard) when the display is in its upright position. In such a case, a torsional stress is applied to a diagonal line of the chassis.
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To solve this problem, Toshiba employed a "honeycomb rib" structure and a "honeycomb beam" structure and applied them to the chassis that faces the LCD display when the notebook PC is closed. The honeycomb beam and honeycomb rib structures were applied to the part that holds the keyboard and the back side of the part that functions as a palm rest, respectively.
The honeycomb beam structure means that the board used for the chassis has many hexagonal holes. Previously, Toshiba used a lattice structure. But, to improve the resistance to twist as mentioned above, the company employed the new structure so that many beams are parallel to the diagonal line to which the stress is applied.
The honeycomb rib structure means that the ribs used on the back side of the chassis have a honeycomb shape. Like the honeycomb beam structure, it enhances the resistance to twist.
The reason why Toshiba did not use the honeycomb rib structure for the part that holds the keyboard is that there is not enough space (height). Also, from the viewpoint of weight reduction, the honeycomb beam is more advantageous.
Moreover, to improve the twist resistance of components mounted by using ball grid arrays (BGAs) such as CPU and chipset, Toshiba used L-shaped plates to reinforce the parts that support the four corners of the BGAs. BGAs are less flexible than PCBs. Therefore, when a torsional stress is applied to the PCB, a strong stress is applied to the four corners of the BGA. To withstand such a stress, the company used the L-shaped plates.
Normally, BGAs are reinforced by using quadrangular backup plates that support their whole surfaces. But Toshiba used the L-shaped plates to reduce weight.