Mainboard PCB Design

Thinking about the widest functionality of the SB81P, one might conjure up a vision of a mainboard all strewn with chips, heatsinks and connectors, and with a whole bunch of cables going out of it. In reality, the developers managed to put all the components on the 280x205 piece of textolite in such a way that they seem to be at a big enough distance from each other. It’s because the components are soldered in groups: the connectors form one group, the controllers form another, etc. Moreover, the mainboard was originally developed with a specific case in mind, so the developers had opportunities to do some optimizations which they actually did.

To avoid confusion I will refer to the part of the mainboard which is closer to the barebone’s front panel as “front part” and to the part which is closer to the rear panel as “rear part”.

The ICE module I have already told you about occupies a big portion of the PCB space. It is located in the front part of the PCB and covers the hottest components, i.e. the processor and its voltage regulator elements.

The chipset’s North and South Bridges are located almost in the center of the mainboard. They are both covered with passive aluminum heatsinks. By the way, you can note a certain rule here – the component density is higher as there’s a bigger distance to the heating components. So, almost all the controllers the mainboard owes its additional functionality to can be found in the rear part of the PCB. Most of the connectors and slots are soldered up here, too. In the assembled system, the power supply hangs over them, thus concealing this densely populated part of the PCB. That is why it seems that there are few components on it at first sight. The highest density is in the mainboard’s right rear corner where there are the following chips: a FireWire400 controller, a hardware monitoring controller, a BIOS chip. The Gigabit Ethernet controller is located to the left, and the audio codec is in the left rear corner.

As for the connectors and slots on the mainboard, there are four fan connectors located near the places where fans are supposed to be. When the cooling system is in use, one connector is left empty, probably to permit you to put an additional small fan on the chipset’s North Bridge. The mainboard’s power connector is split in three parts: in the mainboard’s top right corner, at the rear edge, and in the center. Two parts are placed in such a way that the attached cable wouldn’t block the airflows inside the case. The third part is always empty in our sample of the barebone. The connectors for the front panel of the case are soldered in parallel to the mainboard’s PCB. That is, the mainboard connects to the front-panel ports not with wires but rather by plugging directly into them with its onboard connectors. The rest of the onboard headers are all grouped together in the top rear corner of the mainboard: four SATA slots, one USB 2.0, one LPT, one FDD, one CD_IN, one CD-IN (mini), and one AUX_IN. The IDE slot is located to the left of this group. Despite their being so close to each other, it is easy to connect cables to the connectors. The IDE slot is the only one which is not easily accessed – it is too far below the power supply.

The mainboard’s connectors that go out through the rear panel have been enumerated above.

So, the PCB design of the mainboard is overall good. There are much more good designing solutions than bad ones here.