George,
Thanks for the input.
We have only a few PCB suppliers so what we did was specify three recipes
from the main Chem companies that all produce finishes in the 6 to 18 range.
Rgds,
LS
-----Original Message-----
From: Wenger, George M. [mailto:[log in to unmask]]
Sent: Friday, August 11, 2006 3:49 PM
To: (Leadfree Electronics Assembly Forum); Lester Subrattee
Subject: RE: [LF] [TN] silver embrittlement
LS,
I think some of your questions concerning immersion silver are answered
in our SurFin 2000 paper:
"Immersion Silver Surface Finish: Usage Requirement Test Results &
Production Experience"
By
George M. Wenger & Robert G. Furrow
Lucent Technologies
Princeton, NJ / North Andover, MA
We've test silver up to 45u" think and didn't find any electromigration
or solder joint issues. We also tested an earlier silver that was
plated at 100u" and found electromigration problems. Our current
internal specification for immersion silver thickness is 2 to 20
microinches. Our original specification was 2 to 10 and that was okay
when the only immersion silver on the market was AlphaLevel. Sterling
and AlphaStar both plate thicker than the old AlphaLevel and we, after
lots of testing, changed our specification to 2 to 20. We didn't change
are specifiation because we like thick silver. Actually we prefer thin
silver because we don't use immersion silver as a solderable surface
finish; use immersion silver as a color change indicator to know the
copper below was clean and solderable when plated. We increased our
maximum silver thickness specification so that our board vendors won't
be limited to only AlphaLevel and they could decide whose immersion
silver they wanted to us.
Regards,
George
George M. Wenger
Reliability / FMA Engineer
Base Station and Subsystems Group
Andrew Corporation, 40 Technology Drive, Warren, NJ 07059 (908) 546-4531
[log in to unmask]
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Lester Subrattee
Sent: Friday, August 11, 2006 2:36 PM
To: [log in to unmask]
Subject: Re: [LF] [TN] silver embrittlement
Thinner Silver coating could be prone to shelf life issues and is
probably less robust with respect to handling. I'm not sure if there may
be issues with probes from Electrical test probes penetrating the
surface and exposing copper below.
Thicker Silver will improve shelf life and robustness of the finish.
However, I do believe that going too thick (way past the 20 microinches)
could result in reliability issues.
Joint embrittlement due to incomplete dissolution of the Silver
into the solder could be an issue. This may result in Silver/Tin rich
region at the interface.
Planar intermetallics from the higher percentage Silver in the
joint has been brought up. The recommendation is to keep the Silver
content around
3 percent or less. The effect should be minimal since there is already 3
percent Silver in the Solder.
I am not sure if Electromigration may become an issue as the
thickness goes up too high. I have to review this.
We specify a range of 6 to 18 microinches. That's what the
manufacturers can produce with good yields. A wide enough range is
required to account for the effects of feature size, location, shape
etc.
8 to 12 microinches is a good target.
Hope it helps.
LS
-----Original Message-----
From: Kane, Amol (349) [mailto:[log in to unmask]]
Sent: Friday, August 11, 2006 1:10 PM
To: [log in to unmask]
Subject: Re: [TN] silver embrittlement
Hi,
What are the important advantages/disadvantages between Thin/Thick
Immersio= n Ag Coatings? The difference in specs is 12uins. Are there
any particular = applications where thin silver is preferred over thick
and vice versa?
Thanks,
Amol Kane
M.S (Industrial Eng.)
Process Engineer
Harvard Custom Manufacturing, Inc.=20
941 Route 38 Owego, NY 13827
Phone: (607) 687-7669 x349
[log in to unmask]
www.harvardgrp.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of George Milad
Sent: Friday, August 11, 2006 12:17 PM
To: [log in to unmask]
Subject: Re: [TN] silver embrittlement
Sue,
You have every right to be confused, as the chairman of the plating
committee that put out the specification 4553, I have gone back and
re-read= the specs. The specs refer to thin silver and thick silver.
My apologies for the poor choice of terminology, the intent was to
differentiate between the Alpha Level product which could only produce a
ve= ry thin coating and the rest of the Immersion silvers out there
that could produce = a thicker coating. So "thin" is a spec for Alpha
level only and the "thick" i= s the spec for all other immersion
silvers.
For users not specifying Alpha Level the spec is:
5 uins minimum, typical 8uins-12uins.
Thick silver would be silver at 20uins or higher.
Thicker silver is unnecessary and may give rise to compromised solder
joint strength. I am not sure that embrittlement is the main defect
here, after = all the Pb/free SAC 305 alloy contains 3% silver.
George Milad
(Chairman IPC Plating Committee)
National Accounts Manager for Technology Uyemura International Corp
(UIC)
249 Town Line Rd
Southington CT 06489
[log in to unmask]
Cell: (516) 901 3874
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