Wednesday, September 3, 2008

Breakout Areas Considerations for PCI Express

Within a breakout area (for example, Philips PCI Express PHY ball field, connector pins, or add-in card edge fingers), exceptions to the general trace routing guidelines may occur.

5 mils intra-pair space and 10 mils inter-pair space are allowed in the breakout region. A small section of trace, up to 50 mils, does not necessarily require a reference plane. Length matching should occur as close as possible to signal pins without introducing any tight bends.

Picture shows some techniques used in breakout areas. Side-by-side placement is considered best. Adjacent with a small serpentine is acceptable. Diagonal routing and adjacent placement with a bend are acceptable but not as good as the other techniques.

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