The recommendations for the C4072 package PCB breakout are summarized as follows.
- TX-to-RX isolation must be carefully considered, especially for LR applications
- RX-to-RX isolation for large IL variations must be carefully considered
- Route TX on lower layers rather than RX to avoid trace-to-via coupling
- Provide ~18 mil separation between RX and TX routing layers
- Place GND vias outside BGA pins to improve RX-to-RX isolation
For a 56 Gbps full-density Quad usage, recommendations are as follows:
- TX-to-TX crosstalk
- Worst-case TX victim: Four diagonal aggressors (plus two non-diagonal aggressors separated by a pair of GND balls)
- Middle column of TX pins routed with via length less than 45 mil
- Victims with fewer aggressors can have longer vias
- RX-to-RX crosstalk
- Worst-case RX victim: Four diagonal aggressors (plus two non-diagonal aggressors separated by a pair of GND balls)
- Projected power sum crosstalk at < 14 GHz = –44 dB
- Recommended restriction: Insertion loss delta between RX channels: < 14 dB
- TX-to-RX crosstalk
- For LR RX with 35 dB insertion loss, requirement is 65 dB isolation
- TX routing layer must be at least 18 mil below lowest RX routing layer