routing of differential pairs

Hi I'd like to ask how everyone routes their differential pairs. I'm not about to condem anyone's software ( SW Vendors should maybe take a look at the answers ) but I'm interested how PCB Designers route a board with 256 pairs, 150 microns width and space, 4 imp. controlled layers and the restriction of not being allowed to swap layers once on the inner layers.

From my own experience, differential pair routing has to happen manually, although some improvements in software have helped.

I've got VISULA ( Zuken-Redac ) & Interconnectix ( Mentor ) and know the restrictions that both tools have.

Should diff. pair routing ever become something that the user could give an auto-router then surely the pair needs to be handled as a single entity.

Does your software do this already ... all answers welcome.

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