My comment on 10% silver in solder being an embrittlement problem is for
Sn63 / Pb 37 (Eutectic) solder. Brittle Ag-Sn intermetallics start forming
when silver exceeds 10 % by weight in that alloy. Most other intermetallic
compounds formed with the Sn, like SnCu2, SnCu, Sn2Cu, etc., are what
actually causes solder to stick to the metal being soldered to. These
examples are not particularly brittle.
I would imagine the upper safe limit for silver in Sn25 / Ag10 / Sb would
be different (or nobody would be using it). Perhaps the Antimony allows
higher concentrations of dissolved silver before the brittle AgSn
intemetallics start forming. Do you know what the limit is? I'm curious.
Thanks,
Kirk Mueller
Martin Weiser <[log in to unmask]> on 09/23/99 08:19:53 AM
Please respond to "Leadfree Electronics Assembly E-Mail Forum."
<[log in to unmask]>; Please respond to Martin Weiser <[log in to unmask]>
To: [log in to unmask]
cc: (bcc: Kirk D Mueller/RWS/Raytheon/US)
Subject: Re: [LF] Pb-free Alternatives using Ag
All,
I wanted to add that Sn25Ag10Sb has been used for many years in high volumes for
soldering power die on to Cu heatsink/leadframes. Yes, this solder is quite
strong and brittle, especially compared to Sn37Pb and similar solders. However,
the Ag-Sn and Sn-Sb intermetallics are not the normal cause of failure in these
packages. The most common failure mode is die cracking during cooling of larger
die due to the large CTE mismatch and high solder strength. In general, if the
die survive the initial cooling then they can be thermally cycled thousands of
times without failure.
Regards - Marty
On Wed, 22 Sep 1999 16:24:27 -0700 Kirk D Mueller
<[log in to unmask]> wrote in response to Doug Rohm:
I thought the problem with tin and silver was the formation of brittle
Sn-Ag intermetallics when the silver content exceeded 10 % by weight.
Kirk Mueller
Doug Romm <[log in to unmask]> on 09/22/99 08:48:13 AM
All,
Several of the Pb-free options being offered for use in both solders and
component lead plating include silver (Ag), for example Sn/Ag. In the past
some users of IC components have had concerns/problems with use of Ag in
components because of silver dendrite growth. Is there any concern about
use of Ag in these Pb-free alternatives? If not please provide a brief
technical explanation of why not.
This question may have been raised previously, but I can't find the answer.
Best regards, Doug Romm
Martin (Marty) Weiser, Ph.D.
Product Manager - Plated & Discrete Products
AlliedSignal Electronic Materials (formerly Johnson Matthey Electronics)
Spokane, WA
(509) 252-2757 (phone)
(509) 252-8617 (fax)
[log in to unmask]
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