Practical controlled impedance LVDS routing?

[bitbanger]

Hi Folks -

I see a lot of LVDS at work over long cable, and more and more have been asked to troubleshoot link integrity. I'm designing a small connector breakout board because the proprietary connectors are impossible to probe (as is inside the end-point devices). This is a small board, 1"x3" or so, with a male connector on one end, a female on the other (think micro-miniature DSUB connector) and some low-profile through hole test points meant for a differential probe. There are four differential pairs.

Anyway despite the small board I need to make sure I'm doing my best to maintain signal integrity. Planning on just some 4-layer protos from OSH Park because this is out of pocket.

The trouble I'm having is not the intricacies of the controlled impedance, it's just the logistics of crossing 4 matched pairs across even this small board. If you imagine one connector on the left, one on the right, the signals on the top left have to route to the bottom pins on the right conn. At first I was using the through-hole test points in the middle to get me to another layer so I could cross over, but this really killed ground plane continuity.

I know vias are generally "frowned upon", but I'm wondering: would a good approach be to use vias all near the originating connector, just to get them all in the right "order", then route the 2-3" across the board, in straight fashion? In saying that out loud the way the test points are oriented, it would still make routing a pain, but perhaps less so.

Right now the stackup I'm planning is ground plane on top, two pairs on Inner Signal layer 1, two pairs on Signal layer 2, then ground plan on bottom layer. Thoughts?

Thanks in advance!