I have never heard of an OSP finish being used to coat immersion silver PWBs. Can you provide more information on that? Robust IAg products such as MacDermid's Sterling fully comply to IPC-4553, which is the standard for immersion silver finishes. If it does not meet IPC-4553, it is not immersion silver, and I do not see anything in IPC-4553 concerning OSP coating, but I may not have the latest standard.
There are a lot of immersion silver products out there. Some are much better than others. The only one I recommend is MacDermid Sterling. Read the standard, because there are a lot of important factors that some of the "other" IAg platings do not fully understand or comply with, such as the minimum thickness, maximum thickness, porosity, etc. Most of the "good" products have a co-inhibitor application to prevent oxidation. Many do not. Know and understand just what your plating product is.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Theodore J Tontis
Sent: Thursday, September 26, 2013 12:47 PM
To: [log in to unmask]
Subject: Re: [TN] Immersion Silver Board Finish Tarnishing

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] 
______________________________________________________________________