Chip Footprint effect on Impedance

[azim.roslan]

hello guys,

Is there any effect of chip footprint on PCB with Impedance? What i means is, if the chip footprint is changes, in term of dimension (length), is this changes will affect the impedance performance? Or, the impedance is based on trace design only?

please advice, thanks.

 

[Izeek]

Hello azim.roslan,

Chip footprint varies it's impedance by additional layout parasitics. Generaly it's appreciability grows up with frequency range. But if you have, for example, 50 Ohm chip interface, you can calculate necessary pad width and then correct it on the footprint. Second you can correct PCB stackup for necessary impedance of the known pad width. After you can use S-parameter data to simulate your RF/microwave without any pad parasitic model.

Kind Regards,
Paul