[MacBook Air Teardown] Secret of 5-layered Keyboard [Part 7]

Mar 10, 2008
Nikkei Electronics Teardown Squad
Photo 1: Perspective view of part of the aluminum member (upper unit) on the top face of the lower chassis. The thickness of the portion between the adjacent keys was 1.9mm (photo provided by Hiroshi Nakamura)
Photo 1: Perspective view of part of the aluminum member (upper unit) on the top face of the lower chassis. The thickness of the portion between the adjacent keys was 1.9mm (photo provided by Hiroshi Nakamura)
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Photo 2: Part of the keyboard main unit. The lower part of the key tops was partially transparent so that light incident from below could pass through.
Photo 2: Part of the keyboard main unit. The lower part of the key tops was partially transparent so that light incident from below could pass through.
[Click to enlarge image]
Photo 3: Light shielding sheet
Photo 3: Light shielding sheet
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Photo 4: Transparent light guide plate. Small slits were formed to diffuse light. Five vertically oblong holes received the LEDs.
Photo 4: Transparent light guide plate. Small slits were formed to diffuse light. Five vertically oblong holes received the LEDs.
[Click to enlarge image]
Photo 5: Insulation sheet. Five LEDs were vertically aligned in the gold area on the left side.
Photo 5: Insulation sheet. Five LEDs were vertically aligned in the gold area on the left side.
[Click to enlarge image]

As we continued to break down the keyboard, the Nikkei Electronics Teardown Squad eventually found what Apple persisted in and what it compromised.

As for the keyboard and its peripherals, it is likely the company focused on the following:
1. Slimness of the chassis
2. Rigidity of the chassis
3. Lighting around each key
4. Keys that do not bend when pressed

In contrast, the following is what the company compromised.
1. The number of parts
2. The man-hours required for assembly
3. Weight
4. Convenience in replacing keyboards

The points that the company stuck to are trade-offs. That is, rigidity is sacrificed when slimness is pursued, and thickness increases when a mechanism to emit light around the keys is incorporated. Thickness also increases when rigid support is provided to prevent the keyboard from bending. What solutions did Apple come up with for these conflicting goals?

First of all, if you have time, please watch the video clip showing how the engineers from leading Japanese computer manufacturers broke down the keyboard. The clip includes an uncut scene of the engineers undoing the screws on the back side of the keyboard. You can also hear the voice of a Squad member who attended the teardown operation.

movie Air Teardown: Part 3 (5:03, Japanese)
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The following four points were confirmed after analyzing the keyboard.

Keyboard with a five-layered structure

To achieve the four prioritized goals mentioned above, the MacBook Air adopted a structure composed of individual parts attached to the aluminum member on the top face of the lower chassis (photo 1).

Right under the upper unit are the keyboard main unit (photo 2), a light shielding sheet with a black upper surface (photo 3), a light guide plate with many slits (photo 4) and an insulation sheet (photo 5). This structure makes it practically impossible to exchange keyboards at retail stores.

The upper unit has a 1.9mm aluminum rigid body

The upper unit extends between the keys. It looks like a lattice with key tops protruding from the gaps. The upper unit is 1.9mm thick at the lattice portion. The shape enhanced the rigidity of the upper unit, especially against torsional stress, when compared with the design in which an opening corresponding to the entire surface of the keyboard is formed.

The weight, however, increased. The upper unit weighs 174g including the touch panel, six flexible substrates and the infrared module.

In addition to the keyboard, most of the parts, such as the mainboard, the Li polymer secondary battery module and the 1.8-inch HDD, are attached to the upper unit. These parts look as though they are covered with the lower aluminum plate having a surface curved for higher strength.

The keyboard supported by the upper unit

Under the keyboard is the mainboard equipped with Intel Core 2 Duo, etc. If the keyboard is to be supported on the lower side, a strong supporting member is required between the keyboard and the mainboard.

In contrast, the MacBook Air was designed in such a manner that the keyboard is tightly screwed from the back side to the rigid upper unit by more than 40 screws, thereby preventing the keyboard from sinking. The keyboard does not sink even at its center portion because it is screwed to the upper unit at the lattice portion, too.

The keys illuminated by the underlying light guide plate

The MacBook Air is equipped with light emitting keys for the convenience of typing in airplanes and other vehicles. Before we broke down the machine, we thought that LEDs may be attached to each keys. However, the light sources turned out to be five LEDs vertically arranged in line on the left side.

The light guide plate was irradiated with light incident from the lateral side. Slits were formed at positions to be illuminated on the guide plate. The shielding sheet was used to prevent the light emission from undesired areas.

In this way, the keys are illuminated without increasing the thickness. To tell the truth, we failed to see the keys actually emitting light because we started to break down the machine before we could confirm it.

Questions unanswered

The MacBook Air was designed to ensure the rigidity of entire chassis and the keyboard, and to emit light around the keys without increasing its thickness. But the number of parts, including the screws, was definitely increased, hence the man-hours for tightening these screws. The upper unit, which imparts rigidity to the chassis, was in itself a problem.

Some questions remained unsolved even after the teardown. First, was it the only way for Apple to use more than 40 screws to fasten the keyboard to the main unit? This is not just a problem of additional man-hours. Apple did not use any loosening prevention agent on the screws in this block.

The screws on laptops, however, are highly likely to come loose during use because laptops are more frequently exposed to vibration than desk top computers. Actually, some of the 40 screws in the MacBook Air we broke down were so loose that we could easily unscrew them with a screwdriver. The greater the number of screws used, the higher the probability that one of them comes off.

One of the engineers pointed out that there may be a better way to fix the keyboard except using a hefty 1.9mm-thick upper plate.

Opinions were divided among the engineers as to whether the upper unit was an aluminum die-cast product or cut from an aluminum plate. If it was made by cutting, the workpiece can be processed in an elaborative manner although the processing cost may be considerable.

On the other hand, is it possible to process such an intricate part by die casting? The Squad members and the engineers continued the discussion at a party after the teardown work.

Later on, the Squad conducted interviews and investigations, and learned that at least the base of the upper unit is an aluminum die-cast product. Considering the cost and the time required for the processing, we concluded that it is unlikely that the upper unit was cut from an aluminum plate.