Neck down routing confusion

[Rahul Soni]

Hi, can anyone please tell me how to calculate maximum neck down length of a trace for high speed differential signals?
At how much distance, nacking should be done and what will be the consequences.
Let's we have trace length 100 mils, width 9 mils, height 1 oz and neck down width 5 mils.

Thanks in advance.

 

[KlausST]

Hi,

A more detailed explanation, pictures?

Klaus

 

[marce]

Don't neck down, then you will be less likely to alter th characteristic impedance