|Ask the Experts|
January 31, 2020
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?
|Expert Panel Responses|
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.
Silver finish should not be an issue, just make sure it is not dissolved in the soldering process.
Global Product Champion
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.
Global Director of Customer Technical Support
Alpha Assembly Solutions
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.
Supply Chain 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.
Technical Support Engineer
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.
Senior Manufacturing Engineer
No. Immersion Silver surface finish on component leads should not cause any embrittlement problems.
Ray Prasad Consultancy Group
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.
VP Engineering Services
STI Electronics Inc.
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/
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.
S T and S Testing and Analysis
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.
Vice President, Technical Director
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.
Director New Product Development
Metallic Resources, Inc
|Submit A Comment|
Free Newsletter Subscription
Circuitnet is built for professionals who bear the responsibility of looking ahead, imagining the future, and preparing for it.
Insert Your Email Address