Hi Experts,

I am designing a high-speed measurement board.  The board will have a dozen high-speed signals connected to 2.92 mm connectors.  The signal traces will be routed on the Top layer with through vias at the two ends.  I have been advised to plate the signal traces with 3 - 10 microinches of Gold over 100 microinches of Nickel.  Solder Mask/Conformal Coat will not be applied over the signal traces and via pads.  No components need to be soldered to the signal traces, and 2.92 mm connectors will be screwed to the board.

I am trying to get an understanding of the board fabrication process to determine the finished thickness of the signal traces.  This will help me figure out the trace impedance.  I will appreciate if you can provide answers to the following:


*        The starting Copper thickness for the Top/Bottom layers will be 0.6 mils (1/2 oz).  Will Top/Bottom layers still go through the normal plating process.

*        At what stage will Nickel and Gold be plated on the board.  Also is it plated on the entire board surface or only the exposed locations (signal traces and vias).

*        Is solder mask applied in the final stage (after the ENIG process).

*        What is the expected finished thickness of the signal traces.  I was informed by the Fab personnel that this will be about 2 mils.

Thank you very much for your help.

Regards

Ravinder Ajmani
HGST, a Western Digital company
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