The answer is...
It depends.
The only way to know for sure is to order some boards and test them.
There are two things that could change for RoHS.  The actual material
(to be able to withstand a high temp process) and the board finish.
If you are exactly specifying the brand and type of material to use,
then you should get what you ask for and performance shouldn't change.
If the material isn't adequate for high temp, then the material you need
will have to change and your specification for it, and that may have a
bigger impact on performance than the board finish.  
We tried an ENIG finish prototype once several years ago, but the boards
didn't work.  We never took the time to exactly nail down the root
cause.  We didn't want to go to gold, others were pushing us to try it.
When the board didn't work, that was enough reason for us to not approve
it forever and ever...  
We are using immersion Ag and it is working well for us, so far.

Are your antenna traces covered with soldermask, or are they
plated/tinned?  If covered in soldermask, the board finish should have
very little impact.  Signal will be running in the copper.
If your frequency is high enough the skin effect comes into play, and
different metals have different impedances, etc.  The signal will start
running in the outermost plating material on plated traces, and that
could change the response from HAL boards.


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Selva Suganthi
Sent: April 6, 2006 6:44 AM
To: [log in to unmask]
Subject: [TN] Regd Rohs Conversion - didn't get any reply!!!

Dear All,

Whats the impact for Rohs conversion on PCB? Will the conversion
affects the characteristic impedance of the board?

The situation is as follows

My Board has a  RF antenna trace with  some grounding  vias. We are
trying to convert from HAL finishing to GOLD Flash? will this conversion
affect the impedance of RF antenna trace?



Thanks and Regards
Suganthi



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