The silver bath needs to be maintained well to avoid issues in keeping
the bath running.  When the bath is not maintained do to lack of
production the bath does go south and is expensive to replenish and/or
make up a new one.  We find that the bath need to be monitored for
certain components and when controlled, provides a finish that is good
for at least 1 year, if not more.  Any boards that are stocked are vac
packed, which helps in shelf life.  ENIG is by far the most costly
alternative, with silver close to HASL, and Tin sometimes lower cost.
Poor line setup, control support and production will maybe the cause of
you fab houses feedback on silver.

Jeffrey Bush
Director, Quality Assurance and Technical Support

VERMONT CIRCUITS INCORPORATED
  76 Technology Drive - POB 1890
    Brattleboro, Vermont 05302
      Voice: 802.257.4571.21 Fax: 802.257.0011
           http://www.vtcircuits.com
 

-----Original Message-----
From: Scott Lefebvre [mailto:[log in to unmask]] 
Sent: Wednesday, November 24, 2004 1:43 PM
To: [log in to unmask]
Subject: [TN] Immersion Silver

I just got off the phone with one of our PCB FAB shops and was surprised
on his response to Immersion Silver as a solder finish.  
He suggested that we do not use it as a replacement for HASL and to use
gold instead.  All the things I've read and did research on IAg in 
contraction to he said.   The shop said shelf life is less than 6 months
and tarnish was a big issue.  It was more expensive than ENIG and not
that many shops do it in-house.

My understanding is the shelf life is 6-12 months if stored and handled
properly.  They silver used today has an anti-tarnishing agents to
prevent tarnishing.  I was also under the impression that IAg is less
costly than ENIG.

Your opinion in this matter would be greatly appreciated.

Thank you,

Scott

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