Mail*Link(r) SMTP               FWD>RE>Silver Plating over Copper

To all:

I agree with all the things Dave mentioned and would like to add the
following:

Silver (Ag) plating is frequently used in sensitive rf (radio frequency) and
other high frequency/speed applications.  Ag is used for two main purposes;
first due to "skin effect", silver is one of the better conductors, and
because most electrical current flow is in the outer surfaces of conductors
(where the greatest electrical field intensity and currents are) and Ag is one
of the best.  The other reason is because most Ag compounds and oxides are
electrically conductive, in contrast to Cu's which are generally poor
electrical conductors.  With the exception of gold, most other surface
platings and coating (solder, etc) are lousy conductors and are seldom used
for serious high frequency/speed applications.  If the design is for
microstrip lines, then the Ag plating will be less effective at very high
frequencies >~1 GHz because most of the electrical current flow is between the
surface of the microstrip that is adjacent to the signal reference (ground)
plane and not on the "outer" surface of the microstrip.

Ralph Hersey
[log in to unmask]

--------------------------------------
Date: 7/3/96 6:55 AM
From: ddhillma
     Hi Ed:
     
     Silver plating over copper - that can be a solderability issue if not 
     done correctly. The copper will diffuse through the silver after a 
     period of time and then oxidize making for a solderability nightmare. 
     We have gotten around this issue by making the silver plate very thick 
     - this takes care of the diffusion issue but makes for a more 
     expensive board. Silver plating also likes to tarnish quickly and can 
     be a handling problem on the manufacturing floor. Is there a 
     functional need for a silver plate? Could gold or tin/lead be 
     substituted? A good article on finishes (plus very good references) to 
     look at is "Connector Reliability in The Military Environment", 
     Connection Technology, May 1989, pages 19-22.
     
     
     Dave Hillman
     Rockwell Collins
     [log in to unmask]
     


______________________________ Reply Separator
_________________________________
Subject: Silver Plating over Copper
Author:  [log in to unmask] at ccmgw1
Date:    7/3/96 7:44 AM


This is mostly addressed to PCB fabricators, but anyone else with 
relevant info please e-mail back to me.  One of our new customers has a 
requirement for SILVER PLATING OVER COPPER and then covered with solder 
mask similiar to SMOBC (SMOBC/S ?).  Do any of the shops out there in the 
technet world do this?
     
Secondly, my customer is looking for the best laminate with low Df and 
low Da.  Is teflon the best or would somone recommend another laminate to 
use?  The laminate would the use the above silver-plated copper.
     
Please contact me in any of the following methods: (1) via 
[log in to unmask], (2) [log in to unmask], (3) Ed Valentine at ProTronics, 
Inc. Telephone: (919) 217-0007 or Fax: (919) 217-0050.
     
Thanks . . .      Ed/
     


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