Server design example diff pair question

[fazilduman]

Hello,

I have a question about diff. pair width on Server design, i always thought that we can not change the diff. pairs width on track. But on server design videos the track width is changed. Is there any constrains about the impedance.

Review of Server PCB Layout & Schematic - Part 2: Platform Controller Hub (PCH)
Review of Server PCB Layout & Schematic - Part 2: Platform Controller Hub (PCH) - YouTube

[robertferanec]

Yes, they do it for example under a BGA to go out of the footprint. However, in this case I am also surprised how far they went with thinner traces.

[fazilduman]

Thank you robert