Kerry,
Telcordia-78-CORE Section 3.2.4 SILVER
CR3-15 [52] Silver containing materials shall not be used where there is a possibility of silver migration that could cause circuit malfunction, especially wherre these materials are separated by or associated with materials that can absorb moisture
Although the statement says "shall not be used" it has the qualifier of "where there is a possibility of silver migration". The data I've seen from Ford, Intel, Rockwell, MacDeermid, Alphametals, NCMS, etc. shows that their testing indicates immersion silver passes the Telcordia electromigration test. When I was with Lucent we did electromigration testing of immersion silver surface finish on the technologies (i.e., board materials, solder mask materials, assembly fluxes and processes) we used for telecommunication product and showed we passed the electromigration requirements.
As for 6.1.1.5, currently we are not using immersion silver as a conductor or contact finish. Actually we're using immersion silver as an indicator that the copper it was plated to is clean (i.e., no tin strip or solder mask residue) and should be solderable. I think Section 6.1.1.5 does not stop anyone from using immersion silver as a contact because if you read the second sentence in Section 6.1.1.5 "This restriction also applies to the use of silver in conductive polymeric materials used in the manufacture of PWBs, unless acceptable reliability data is provided to the Network Operator or its designaed representative." The ws I read this requirment is that you can use immersion silver if you've done your homework and have generated the acceptable reliability data.
I don't have the latest "McDonald billboard style numbers" indicating the number of billions of solder interconnections made to immersion silver boards but if you look at the IPC National Conference On Surface Finishes and Soldering in the 1997 to 199 time frame and the SurFin 2000 proceeding I think you'll find that there have been millions of boards with immersion silver surface finish sold to Telcordia customers.
Regards,
George
George M. Wenger (908)-546-4531 [log in to unmask]
Distinguished Member Technical Staff
Celiant Corporation, FMA Lab, 40 Technology Drive, NJ 07059
-----Original Message-----
From: McMullen, Kerry [mailto:[log in to unmask]]
Sent: Friday, April 19, 2002 9:08 AM
To: 'TechNet E-Mail Forum.'; Wenger, George M.
Subject: RE: [TN] Immersion Silver
Hi George,
Thanks for the reply.
One final question I have for Technet.
Bellcore GR-78-CORE:
Section 3.2 Materials
3.2.4 regarding Silver.
Then check, Section 6.1.1 Printed Wiring Board Requirements:
6.1.1.5 Conductor Materials and finishes R6-8 Silver shall not be
used as a conductor or contact finish.
Am I to understand I cannot ship an Immersion Silver board to a customer
that requires we adhere to Bellcore standards? Is the Bellcore standard
changing?
Thanks,
Kerry
-----Original Message-----
From: Wenger, George M. [mailto:[log in to unmask]]
Sent: Thursday, April 18, 2002 9:31 PM
To: [log in to unmask]
Subject: Re: [TN] Immersion Silver
Kerry,
What you heard is partially correct. The exception I take in the statement
is that you need to make sure that your soldermask is compatible with any
finial finish that is applied to PWBs after the solder mask operation. It is
my understanding that because of the chemicals and low temperature (compared
to other finial finishes)associated with immersion silver replacement
plating the solder mask concern is no worst than other finial finishes. In
fact there are some fabricators that apply NiAu finial finishes prior to
solder mask because the sodler mask they use is affected by the electroless
nickel plating chemistry.
The finial finish needs to be selected based on design, fabrication issues,
solder joint integrity/reliability, availability, and cost. If you're doing
SMT reflow of fine pitch components and are required to use 3 to 6 mil thick
stencils you probably need to avoid HASL. If you're building 2 to 4 GHz RF
products on low low subtrates with long microstrips you probably need to
avoid the use of NiAu or at least make the nickel plating real thin (25-50
micro inches) which presents problems to fabricators. If your fabricator
has problems controlling tin-strip and solder mask processes you probably
need to avoid OSP. If you fabricator privides boards wrapped with rubber
bands or in brown paper or if you place boards on trays after reflow
assembly rather than in metal racks you proably want to stay away fro
immersion silver. If you need to do wire bonding you'll probably windup
using thick electrolytic or electroless gold or you might even get away with
ENIG. On the other hand if you're using 1mm or smaller pitch CSP or area
array packages or high I/O BGAs you probably need to know as much as
possible about "Black Pad"
Sorry for the long winded answer but my point is you need to assess the
compatibility, interactions and requirments associated with fabrication,
assembly, and use in order to decide what finial surface finish works for
your application.
-----Original Message-----
From: McMullen, Kerry [mailto:[log in to unmask]]
Sent: Thursday, April 18, 2002 3:57 PM
To: [log in to unmask]
Subject: Re: [TN] Immersion Silver
Hi Earl / Rick F.
I am still doing my research. I recently heard you have to make sure that
your soldermask is compatible with the Immersion Silver process. That is
where I am at now in my evaluation.
Rick F. made some good points. NiAu , Ag, Sn, HASL should be selected based
on the design. For example, I would rather press compliant pins into HASL
plated through holes than NiAU holes.
Cheers,
Kerry
-----Original Message-----
From: Earl Moon [mailto:[log in to unmask]]
Sent: Thursday, April 18, 2002 2:59 PM
To: [log in to unmask]; McMullen, Kerry
Subject: Re: Immersion Silver
Kerry,
You helped me greatly with your reflow profile. Help me, and us all, again
with the results of your silver findings.
Earl
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