Main board design improved

The main board functions were integrated into a single piece, which mounts most of the major components on the side of the display (Fig 2). In the first-generation (2G) iPhone, the wireless circuit board was separate from the main board.

"The design has quite advanced and come close to the level of main board sseen in Japanese handsets," said the engineer from a Japanese handset manufacturer.

Fig 2: The iPhone 3G's main board. Major components packaged on one side. Many of the key components including RF circuit, base band circuit and application processor are mounted on one side (the side of the display) of the substrate. Only a few components including flash memory and wireless LAN/Bluetooth transmission module are embedded on the side of the Li-polymer secondary battery. It measures about 84.3 x 53.8mm with a thickness of about 0.7mm. It appears to be an 8-layer substrate. The names of the manufacturers and the purposes of the components were estimated by Nikkei Electronics.
[Click to enlarge image]

Fig 3: A sign of Apple's struggle to cut down on noise? The stainless shields that covered the main board seen from the back side. Apple seems to have plated copper on the back of the shield that covers the area where application processor, display interface IC and touch panel controller IC are packaged, to enhance its measures against noise.
[Click to enlarge image]

The RF circuit part, to which W-CDMA/HSDPA function was added, employed a chipset of Infineon Technologies AG of Germany.

"Apple appears to have added little arrangement to Infineon's reference design," the engineer said.

The company equipped the iPhone 3G with three units of TriQuint Semiconductor Inc's W-CDMA/HSDPA power amplifier/duplexer modules to support four frequency bands and make the handset usable all over the world.

"If the handset were dedicated only to SoftBank Mobile (Japanese carrier for the iPhone 3G), it would require only one module," the engineer said.

Fig 4: More measures against noise found in the display part. The LCD panel and the touch panel mounted in the iPhone 3G. The 2.2mm-thick LCD panel is a product of Sharp Corp. The flexible substrate is coated with dielectric paste, which seems to prevent noise.
[Click to enlarge image]

Meanwhile, Apple seems to have struggled to cut electromagnetic noise around the main board. Only the back of the shield covering application processor, display interface IC and touch panel control IC is plated in copper (Fig 3). It seems to be aimed at strengthening measures against noise.

"Apple may have added it later when it found a problem during the prototype stage," an engineer from a handset manufacturer said.

The flexible substrates of the LCD panel display and the touch panel are coated with dielectric paste, which appears to be aimed at preventing defective display caused by electromagnetic noise and malfunction of the touch panel (Fig 4). This is possibly related to the fact that the touch panel controller IC is mounted on the main board.

"As touch panels often malfunction due to electromagnetic noise, a touch panel controller IC is usually located as close to a panel as possible by, for example, mounting it on a flexible substrate," the engineer said.