Hi Kevin - there is a reasonable body of data documenting the use of the
Sn62 solder alloy for minimizing the leaching of silver into a solder
joint during solder processing. The effect is not large but has been used
widely throughout the industry. The addition of the 2%Ag content to the
Sn62 tin/lead alloys slows down but does not stop the dissolution of
silver from the item you are soldering. The AWS Soldering Handbook (ISBN
0-87171-618-6) has some information and a google search should yield some
published papers. The topic of silver acting as a solder joint reliability
improvement constituent for SnPb alloys is a much more controversial
topic. As Werner detailed, silver as been shown to strengthen solder
properties but how/if that characteristic improvement results in a
practical improvement of the solder joint is still a lively discussion.
The majority of the industry has utilized the Sn62 for its
leaching/wetting characteristics (i.e. tombstoning of small SMT chip
components) rather than for a solder joint reliability reason.

Dave Hillman
Rockwell Collins
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[TN] silver solders and thermal fatigue resistance






Greetings,

Can anyone provide a simple description of or provide/recommend articles
regarding the role of silver addition in solders?  I've seen reference in
several articles that it was originally used as a means to mitigate
migration of silver when soldering to thick silver deposits.  I've also
seen reference that it also increases the thermal fatigue resistance.  The
latter is what I am most interested in, and would like to better
understand the "why's".

Thanks,
Kevin Glidden


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