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48 The PCB Design Magazine • June 2014 will be used can make DDR3 layout much eas- ier. Assigning different colors to each memory group helps to visually define the interface. A microvia (µvia) takes less space than a through- hole via, allowing for fanout of more tracks in the same area. Microvias also save space on oth- er layers, and the extra free space there can then be used for routing. Why use Microvias for Address, Command, and Control Signals? The address, command, and control groups have the highest number of signals out of the memory groups. If through-hole vias are chosen when routing these groups, a lot of space will be wasted on every layer. By instead choosing article RoUTINg DDR3 MEMoRY AND CPU FANoUT continues Figure 5: Two or three tracks can fit between microvias, in the same space needed for one track between through-hole vias. Figure 6: Some of the address, command, and control tracks have to be routed under the pads of the closest groups.

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