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December 14, 2017

Concerns With Silver Finish Component Leads

A few of the components we are using are have leads with silver finish. Will silver cause solder embrittlement like gold? Is removal of silver needed or can it be soldered as is using Sn63Pb37 solder?

S.A.

Experts Comments

Silver as an alloying addition to SnPb solder will change the mechanical properties of the solder, making it somewhat stronger and stiffer, however at concentrations up to 2% (there is a ternary eutectic near 62SN36Pb2Ag) there is no risk of embrittlement. Because the solder is stiffer, however, it can change the response to both thermal cycling and shock.
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Fritz Byle
Process Engineer
Astronautics
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.
Silver finish should not be an issue, just make sure it is not dissolved in the soldering process.
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Richard Boyle
Global Product Champion
Henkel Electronics
Richard Boyle is a Global Product Champion at Henkel Electronics. He has over 25 years experience in the electronics assembly industry and is responsible for the global technical service of all of Henkel's solder materials.
The silver will quickly alloy with the tin in the lead free alloy, but you will not have the same issue as you would with gold. Gold will embrittle the lead free alloy at concentrations above 3%. Silver increases the resistance to thermal cycling failures in tin based alloys.
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Mitch Holtzer
Global Director of Customer Technical Support
Alpha Assembly Solutions
As the Global Director of Customer Technical Service (CTS) for Alpha, Mitch sets direction and provides coordination for the Alpha CTS group in a global capacity. A major focus of this position is to provide strategic support to OEM, CEM and Automotive customers and target accounts. Mitch joined Alpha in 1998 and has progressed through positions of increasing responsibilities in Marketing, Product Management and R&D. He is a graduate of Purdue University with a degree in Chemistry and holds an MBA from Temple University.
The issue you will face is that the silver will leach from your component leads into the solder joint. This means the unfinished leads will now be exposed to corrosion. The best thing is to dope your solder with a small amount of silver, (generally 2%). Your solder supplier will have sn62pb36ag02. This will stop the silver from dissolving into your solder joint. A side benefit is your joints will be cosmetically shinier.
Paul Dickerson
Supply Chain Engineer
Matric Group
Mr. Dickerson is an engineer with 20 years of manufacturing experience. He has worked supporting SMT, THT, cable assembly, and box build processes. He is a Certified SMT Process Engineer.

Ag does stiffen Sn containing solders through the formation of AgSn intermetallics that act like scaffolding in the solder joint.

But before we ring the alarm bells keep in mind that Sn62 (62Sn 36Pb 2Ag) was a very popular alloy until the advent of Pb-Free. And many other Sn based alloys contain Ag such as 95Sn 5Ag, 96.5Sn 3.5Ag, SAC305 (96.5Sn 3.0Ag 0.5Cu), SAC405 (95.5Sn 4.0Ag 0.5Cu)... So Ag can actually provide some desired characteristics in a solder alloy.

With all that said, there is the separate issue of how much Ag is present. It is unlikely that a silver plated lead would add enough Ag to a solder joint to significantly alter the mechanical properties of the solder joint.
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Eric Bastow
Senior Technical Support Engineer
Indium Corporation
Eric is an SMTA-certified process engineer (CSMTPE) and has earned his Six Sigma Green Belt from the Thayer School of Engineering at Dartmouth College. He is also a certified IPC-A-600 and 610D Specialist. He has an associate's degree in Engineering Science from the State University of New York and has authored several technical papers and articles.
Were the terminations dipped in silver or electroplated? It is recommended to use a SAC alloy when dealing with components with silver terminations. This SAC alloy will create a stronger inter-metallic layer vs. one created with tin-lead.
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Edithel Marietti
Senior Manufacturing Engineer
iDirect
Edithel is a chemical engineer with 20 year experience in manufacturing & process development for electronic contract manufacturers in US as well as some major OEM's. Involved in SMT, Reflow, Wave and other assembly operations entailing conformal coating and robotics.
No. Immersion Silver surface finish on component leads should not cause any embrittlement problems.
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Ray Prasad
President
Ray Prasad Consultancy Group
Ray Prasad is the founder of Ray Prasad Consultancy Group which provides teaching, consulting and technical expert services in tin-lead and lead free technologies using SMT, BGA, BTC, fine pitch and through hole components. Mr. Prasad is a long time member of IPC, and is currently the chairman of BGA committee IPC-7095 "Design and Assembly Process Implementation for BGA" and Co-Chairman of recently created IPC-7093 "Design and Assembly Process Implementation for Bottom Terminations" surface mount Components (BTCs) such as QFN, DFN and MLF.

Really good question - would have liked a little more information but here is an answer I think addresses why you are asking the question.

Silver plating is normally immersion silver plating for electronic applications. I am assuming you are referencing immersion silver plating which is an electroless plating process that is used as an oxidation barrier for copper pcb pads and used on some copper alloy leads on certain component types. If this is truly the case then you have nothing to worry about from an embrittlement standpoint because the immersion silver plating thickness is usually 4 to 16 microinches - which you should validate. At these nominal thicknesses the solder alloy will absorb the silver into its 63/37 tin lead alloy without negative effects.

Now if it is above 16 microinches then one should be asking why this is being performed and the component parts may need to be tinned before use. That raises another question on reliability and should be reviewed with vendor for proper processing parameters of their component parts. Remember certain component lead frames use aluminum wirebonds which uses immersion silver plate so that the die inside your package is wirebonded to the immersion silver plate which then leads to a silver plated lead finish on finished component. Good luck and hopefully this sheds some light on silver plated leads.
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Mark McMeen
VP Engineering Services
STI Electronics Inc.
Mark T. McMeen is STI Electronics Inc.ʼs Vice President of Engineering Services. He oversees the daily operations of the Engineering Services division of STI. He has over 18 years experience in the manufacturing and engineering of PCBs.

Both silver and gold can cause embrittlement in 63Sn/37Pb solder joints. Normally, the concentration of silver or gold has to reach greater than 3% by weight in the solder joint for this to occur, but failures with lower concentrations have been found. Please refer to this IPC blog for more information.

https://blog.ipc.org/2009/04/20/gold-au-and-silver-ag-embrittlement-of-solder-joints/

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Tony Lentz
Field Applications
FCT Assembly
Tony has worked in the electronics industry since 1994. He worked as a process engineer at a circuit board manufacturer for 5 years. Since 1999, Tony has worked for FCT Companies as a laboratory manager, facility manager, and most recently a field application engineer. He has extensive experience doing research and development, quality control, and technical service with products used to manufacture and assemble printed circuit boards. He holds B.S. and M.B.S. degrees in Chemistry.
Ag3Sn platelets will form in the solder joint and are embrittling similar to AuSn4 but the necessary weight percentage to cause an issue is unlikely to occur. The use of silver plated devices is common and are not Pretinned to removed the surface finish plating.
Gerard O'Brien
President
S T and S Testing and Analysis
Gerald O'Brien is Chairman of ANSI J-STD 003, and Co Chairman of IPC 4-14 Surface Finish Plating Committee. He is a key member of ANSI J-STD 002 and 311 G Committees Expert in Surface finish, Solderability issues and Failure analysis in the PWA, PWB and component fields.

From my understanding, the silver will go into solution and not be a problem for the strength of the joint. However the exposed silver will be impacted by the environment in which it is placed. Silver oxidizes quickly in the presence of sulfur and will turn black. We've seen silver plated leads back 40 plus years ago on TI ICs and eventually the silver plating peeled off the leads leaving the base material exposed. Secondly we also experienced silver migration, which shorted out between the component leads. This is why we discontinued the use of silver plated component leads.

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Leo Lambert
Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.
Small amount of silver from component will not cause reliability issue metallographically in solder joint. However, silver leaching may weaken the interface between component lead and bulk solder.
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David Bao
Director New Product Development
Metallic Resources, Inc
David Bao has more than fifteen years of experience in developing new solder paste, wave soldering fluxes and other SMT consumables. He currently serves as the Director of New Product Development at Metallic Resources Inc. He received a Ph.D. in Chemistry at Oklahoma State University.
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