Steven -
 
I had to look a bit in some old files to see the formal reference between "thin immersion silver" and "thick immersion silver".  The first IPC 4553 standard, dating to 2002-2004, did make a formal difference between those.  
 
However, by the time of the 4553A revision, around 2008 or 2009, the formal difference was discarded.  The allowed thickness included the range formerly covered by "thin" and "thick".   
 
While I only know a limited amount about the "chemistries", my impression is that today there is no chemistry for thin and for thick.   Bob Lazzara has previously pointed out that dwell time and temperature can change the immersion silver thickness.  

Denny Fritz
 
 
-----Original Message-----
From: Steven Kelly <[log in to unmask]>
To: TechNet <[log in to unmask]>
Sent: Mon, Aug 10, 2015 3:47 pm
Subject: [TN] immersion silver


Hi All,
Why would someone choose thick immersion silver over thin? Are these
different chemistries? Regards Steve Kelly


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