How to route differential pairs?

[shai]

Background: I'm making an OpenPNP pick and place board that runs on smoothieware. I am creating a USB 2.0 Hub (since LPC1769 chip uses USB 2.0) for the two cameras and smoothie so I can connect my machine using one USB cable instead of three. I've already tested it and it works.

I have an FFC connector that runs to the head of the PNP head. Two of the traces on the FFC are for the downward facing camera. This FFC connector needs to be placed where it is currently on the board (assume I cannot move it) and assume the HUB on the right side in the attached pictures also cannot be moved. What's the best way to route the differential pairs from the FFC on the left to the Hub Controller on the right?

The board is 4 layer board (from top to bottom):
TOP (traces) with GND pour
GND pour only
VCC (12V pour, 3.3v pour)
BOTTOM GND pour (with traces)

I was thinking of routing these pair of differentials on the bottom of the board where there's no components (ok, it goes under a few components on the left side only). Am I transferring between layers correctly? I did some research but couldn't find much on how to transfer differential pairs between layers correctly.. or is it fairly simple? Any help appreciated!! The lengths are matched 100%

P.S. Would this long routing from left to right for the downward camera work in theory? lol
See attached images.

[ataradov]

It is only Full-Speed USB, you will be fine. You also don't need that length matching kink in the trace. Place a row of vias along the pair, you seem to have plenty of space for that.

[shai]

What's the purpose of placing the Vias along the traces on the sides? Should they be GND and 12V Vias on opposite sides? Can you show a quick drawing to make sure I understand correctly?

[ataradov]

What's the purpose of placing the Vias along the traces on the sides? Should they be GND and 12V Vias on opposite sides? Can you show a quick drawing to make sure I understand correctly?

Both sides should be grounds, at least along the USB traces. They will forms a "shield" of sorts, preventing EMI from both sides.

I assume you have ground polygons on both sides. Because that is something you should actually do. Then just place a bunch of vias along the traces.

Here is a random picture from Google to illustrate the idea. But there is no need to have them this dense, every 1/4"-1/2" will be sufficient and won't annoy your board house.