BGA DDR packages have a unique footprint. There are two columns of pads on both sides of the device, and an empty column in between.

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Is there a reasoning behind the placement of these pads (in terms of PCB layout), or is this just a consequence of the design of the ddr3 silicon die?

More specifically, what I am wondering is, are there any tips/tricks/guidelines to place DDR modules on both sides of the board, directly across, or very close to each other?

  • \$\begingroup\$ I don't know, but I wouldn't be surprised if the footprint is patented and can be licensed (read: "payed for") by other manufacturers. \$\endgroup\$ – jippie Mar 13 '13 at 18:22

You can take a look at a DDR3 die and Xray photo of the same chip here : http://chipworksrealchips.blogspot.com/2011/02/how-to-get-5-gbps-out-of-samsung.html

You can see that the memory is organized along a central spine and that the pad are placed along this spine. I can't tell you more about the internal layout as it's not my field of expertise.

For DDR PCB layout you can read this Application Note :

For the chips' placement it's more a signal integrity issue as the timings are sensitives. If your PCB and process technologies allows you any placement and your design is compliant with DDR/DDR2/DDR3 standard (mostly timing constraints) you are free to go with it.

I haven't seen a board with DDR3 memories for the moment, I only worked with a board with DDR2 chips. The five chips were placed on the same side (same or opposite side of the CPU) and side by side.

I can only recommend you to simulate your DDR design to be sure that your placement and routing are ok.

  • \$\begingroup\$ zeqL, the chip in your first link is actually a GDDR5 chip, not a DDR3 chip. \$\endgroup\$ – lamont cranston Jul 7 '15 at 21:13
  • \$\begingroup\$ It doesn't change the meaning of my answer :) GDDR and DDR are not so different after all. \$\endgroup\$ – zeqL Jul 8 '15 at 19:46
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    \$\begingroup\$ For those who came here later and the link to the "how to get 5 gbps out of ..." link, here is I think the original source: chipworksrealchips.blogspot.com/2011/02/… \$\endgroup\$ – hak8or Aug 8 '17 at 23:02

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