Hi Larry! Which is better - Sn 62 or Sn63? Which came first - the chicken
or the egg? You will find that there are two very distinct opinions for
your question. One opinion is that there is no difference between the two
solder alloys and they are identical/interchangeable. The second opinion is
that the Sn62 has better wetting characteristics and better thermal fatigue
life characteristics. Metallurgically, the Sn62 alloy has slightly better
surface tension values than Sn63 (376 dynes/cm versus 490 dynes/cm) and
it's solidus is a few degrees lower that Sn63 (179C versus 183C). Some
technologists have equated these physical property values as improved
wetting characteristics. You will also find two distinct sets of thermal
fatigue life data - one set which shows no improvement using Sn62 and
another which shows a definite improvement. It's my opinion that the
thermal data is being influence by the interaction of the assembly use
environment and specific assembly design/construction issues. The original
use of the Sn62 alloy was to reduce the leaching/diffusion problems
associated with ceramic chip capacitor end terminations. The implementation
of barrier plating as nickel or copper on chip capacitors end terminations
has eliminated the need for Sn62 in those cases. Fritz Byle, Doug Pauls,
and I have an annual 'Sn63 versus Sn62 solder alloy debate' over a couple
of beers at the IPC Works and/or APEX meetings - you are welcome to join us
at the next meeting. Good Luck.

Dave Hillman
Rockwell Collins
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Larry Koens <[log in to unmask]>@IPC.ORG> on 07/25/2001 03:10:07 PM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
      to Larry Koens <[log in to unmask]>

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Subject:  [TN] solder paste with 2% silver


Got a question for everyone,

I just switched companies and the new company that I'm with now uses a
62/36/2 solder paste. I've always used the 63/37 formula. The guys who
decided to use the 2% silver are no longer with the company. My question
to you is, why would they want the 2% silver in the paste? They know
something I don't?!

Thanks,
Larry

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