Lead/Terminal Finish details for all Si5338/Si5335/Si5330 family of devices:

Ni : 10 u'' ( Min ) 
Pd : " 0.1 u'' ( Min ) 
Ag- Au alloy : 0.2 u'' ( Min ) Silver content is very low. 

If you require more detail on lead finish, please work through your Silicon Labs sales rep to submit a RFI (Request For Information) with the details of the additional information you need.