One of the leading mobile phone companies on the planet uses Sn63 based on
its experience and studies of the literature. And another equally prominent
leading company has conclusive evidence that only Sn62 should be used.
Other than that IMHO, outside of the leaching effect on thick film, there is
not much logic in this zone.
The only strong opinion I have is that the use of silver does not make Sn62
brighter and shinier than Sn63. The opposite on larger joints actually, as
slow cool down can give a slight frosted appearance to some joints.
As its Friday, here is a non technical supplementary answer:
As a simple pragmatist I merely observe that those companies that were
making hybrid Thickfilm circuits -and therefore already using solder paste
when surface mount on FR4 started to be done - simply carried on using the
solder paste they already had specified. Naturally this was Sn62. At that
time this was a cost free decision and was perfectly valid. Those that were
using Sn62 then tend to be the ones using it now.
Those that came to SMT from though hole and therefore using Sn63 for wave
soldering either continued to use the same alloy in their solder paste as
their preferred alloy. Or they were advised that it was OK to use Sn62 by
established paste suppliers because that was the alloy they were used to
supplying. The arguments about which was best didn't come till later. But
these arguments don't include a section on corporate inertia.
Of course its much more fun to have a non ending technical discussion in
this zone, so take your pick which way you will go :).
Regards
Mike
* Please think before you print
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Thursday, July 15, 2010 1:18 PM
To: [log in to unmask]
Subject: Re: [TN] silver solders and thermal fatigue resistance
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
[log in to unmask]
"Glidden, Kevin" <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
07/14/2010 12:24 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
"Glidden, Kevin" <[log in to unmask]>
To
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cc
Subject
[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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