Layer Count Estimation
A quick way to estimate the number of signal routing layers required to fully break out signal pins from
the FPGA would be to use the following equation:
For Xilinx® FPGAs, MPSoCs/RFSoCs, and ACAPs, the quantity of signals is approximately 60% of the number of BGA balls. The other 40% are power and ground signals that are most often routed directly down to their own dedicated planes by vias. The equation assumes full I/O utilization. If fewer I/Os are used, the number of signals to route goes down accordingly.
Routing channels are the number of available routing paths out of the BGA area
(the number of BGA pins on one side minus one, times four sides). The following
figure shows a 5x5 grid with sixteen total routing channels (four routing channels
per side times four sides).
Figure 1. Definition of Routing Channel
(16
Total Routing Channels Shown)
(16
Total Routing Channels Shown)
Routes per channel is either one or two, depending on whether one or
two signals are routed between BGA pads. The approximate number of signal layers
required to fully route out a Xilinx FPGA or ACAP are shown in the following
table.
| BGA Pins | Ball Pitch (mm) | Routing Channels | Estimated Signal Layers Required with All Available I/Os Routed | |
|---|---|---|---|---|
| One Trace Per Routing Channel | Two Traces Per Routing Channel | |||
| 196 | 0.5 | 52 | 2 | 1 |
| 196 | 1.0 | 52 | 2 | 1 |
| 225 | 0.8 | 56 | 2 | 1 |
| 236 | 0.5 | 56 | 3 | 1 |
| 238 | 0.5 | 56 | 3 | 1 |
| 256 | 1.0 | 60 | 3 | 1 |
| 324 | 0.8 | 68 | 3 | 1 |
| 400 | 0.8 | 76 | 3 | 2 |
| 484 | 0.8/1.0 | 84 | 3 | 2 |
| 485 | 0.8 | 84 | 3 | 2 |
| 494 | 0.5 | 84 | 4 | 2 |
| 530 | 0.5 | 88 | 4 | 2 |
| 625 | 0.8 | 96 | 4 | 2 |
| 676 | 1.0 | 100 | 4 | 2 |
| 784 | 0.8/1.0 | 108 | 4 | 2 |
| 900 | 1.0 | 116 | 5 | 2 |
| 1024 | 0.92 | 124 | 5 | 2 |
| 1154 | 1.0 | 132 | 5 | 3 |
| 1155 | 1.0 | 132 | 5 | 3 |
| 1156 | 1.0 | 132 | 5 | 3 |
| 1157 | 1.0 | 132 | 5 | 3 |
| 1365 | 0.92 | 144 | 6 | 3 |
| 1369 | 0.92 | 144 | 6 | 3 |
| 1517 | 1.0 | 152 | 6 | 3 |
| 1596 | 0.92 | 156 | 6 | 3 |
| 1759 | 1.0 | 164 | 6 | 3 |
| 1760 | 0.92/1.0 | 164 | 6 | 3 |
| 1761 | 1.0 | 164 | 6 | 3 |
| 1923 | 1.0 | 172 | 7 | 3 |
| 1924 | 1.0 | 172 | 7 | 3 |
| 1925 | 1.0 | 172 | 7 | 3 |
| 1926 | 1.0 | 172 | 7 | 3 |
| 1927 | 1.0 | 172 | 7 | 3 |
| 1928 | 1.0 | 172 | 7 | 3 |
| 1930 | 1.0 | 172 | 7 | 3 |
| 2104 | 1.0 | 180 | 7 | 4 |
| 2197 | 0.92 | 184 | 7 | 4 |
| 2377 | 1.0 | 188 | 8 | 4 |
| 2577 | 1.0 | 200 | 8 | 4 |
| 2785 | 0.92 | 208 | 8 | 4 |
| 2892 | 1.0 | 212 | 8 | 4 |
| 3340 | 0.92 | 228 | 9 | 4 |
| 3824 | 1.0 | 244 | 9 | 5 |
| 4072 | 1.0 | 252 | 10 | 5 |
| 5601 | 0.92 | 296 | 11 | 6 |