From what I remember from Chemistry and Physics, Silver Oxide has a 
considerably higher conductivity then pure silver.  In the military all 
of the high reliability connections were plated with Silver and we were 
taught to never clean off the tarnish.     At the power plant most of 
the high reliability joints are silver plated, for our 500Kv 
transmission lines all of the Copper and Aluminum buss work bolted 
splices are Silver plated.

Pat

On Thu, Sep 26, 2013 at 10:29 AM, Rueda, Ernesto wrote:

> 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
>  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] 
______________________________________________________________________