Hi Gerry - yes, you hit one of those "odd" element characteristics. Silver 
oxide is as conductive as elemental silver which is an unusual 
characteristic for a metal (and one reason RF circuit designers like ImAg 
as a pwb finish). Ernesto may be seeing oxidized copper that has diffused 
thru the silver surface finish which would cause solderability issues.

Dave



From:   Gerry Gagnon <[log in to unmask]>
To:     <[log in to unmask]>
Date:   09/26/2013 02:56 PM
Subject:        Re: [TN] Immersion Silver Board Finish Tarnishing
Sent by:        TechNet <[log in to unmask]>



Hi Ted,
 
Not 100% sure, but I believe silver and its' oxide(s) are highly 
conductive.
 
I suspect the "oxide" Ernesto is seeing is not silver or its' oxide.
 
Just my $0.02.
 
Gerry
 
> Date: Thu, 26 Sep 2013 17:47:14 +0000
> From: [log in to unmask]
> Subject: Re: [TN] Immersion Silver Board Finish Tarnishing
> To: [log in to unmask]
> 
> Ernesto,
> 
> Look at the boards you are having issues with test. Is it possible the 
ones you are having problems with went through the reflow process first?
> 
> I ask because with an immersion silver finish there is typically an OSP 
finish to help prevent the silver from tarnishing. So unless the boards 
went through half the SMT process you should have had no problems related 
to them being out on the shop floor.
> 
> If the boards are having issues at test and you are in fact hitting test 
points with silver finish on them I would suggest you change your test 
probes to a sharper point or, print paste on the test pads. After the SMT 
process the silver finish is going to tarnish creating interment 
connections during test. This would also be dependent on how long the 
boards have been in process i.e. rework. The longer the boards are in 
process prior to testing will increase the problem with interment contact 
with test points during test.
> 
> Ted T. 
> 
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Rueda, Ernesto
> Sent: Thursday, September 26, 2013 12:30 PM
> To: [log in to unmask]
> Subject: [TN] Immersion Silver Board Finish Tarnishing
> 
> 
> Hi all,
> 
> I am seeking recommendations from the experts of this forum about 
tarnishing of the PCB board finish with Immersion Silver.
> 
> Please enlighten me about the minimum thickness of silver metal on top 
of the copper layer. 
> What is the maximum process time limitation to build these boards?
> 
> Our SMT machine was down for more than 3 days that went through the 
weekends and the boards were not completed. 
> It is possible that varying temperature and humidity affected some of 
the assemblies. 
> We have problems with testability at some test points because of the 
tarnishing issues.
> 
> We are planning to send out some panels for plating thickness test and 
contamination tests as well.
> Any provider that you may recommend?
> 
> 
> Thank you in advance.
> 
> Ernesto
> 
> 
> Ernesto V. Rueda   |   PELCO by Schneider Electric   |   SMT Process 
Engineer
> Phone: +1 559-292-1981 ext. 3848  |   Fax: +1 559-388-3781  |   Mobile: 
+1 559-333-3913
> Email: [log in to unmask]    |   Site: www.pelco.com | 
  Address: 3500 Pelco Way, Clovis, CA  93612-5699 USA
> P please consider the environment before printing this email
> 
> 
> 
> 
> ______________________________________________________________________
> This email has been scanned by the Symantec Email Security.cloud 
service.
> For more information please contact helpdesk at x2960 or 
[log in to unmask] 
______________________________________________________________________
> 
> ______________________________________________________________________
> This email has been scanned by the Symantec Email Security.cloud 
service.
> For more information please contact helpdesk at x2960 or 
[log in to unmask] 
> ______________________________________________________________________
  

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________




______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________