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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