Hi Poh! This is one of those occasion's when both numbers are correct! The
"true" tin/lead eutectic composition is 61.9% tin and 38.1% Pb with a
melting temperature of 183C. The addition of silver lowers the melting
temperature slightly - Sn62/Pb36/Ag2 alloy is a near eutectic alloy with a
melting range of 177C-189C.  Additionally the Sn63/Pb37 alloy is a near
eutectic alloy with a melting range of 183-187C. Solder alloy surface
tension also plays a role in tombstoning. Take a look at the Technet
archives - there was a lengthy discussion of the tombstone/solder alloy
topic some time ago.

Dave Hillman
Rockwell Collins
[log in to unmask]




                      Poh Kong Hui
                      <[log in to unmask]        To:       [log in to unmask]
                      M.SG>                    cc:
                      Sent by: TechNet         Subject:  [TN] Solder Paste with 0.4% silver
                      <[log in to unmask]>


                      03/22/2003 05:50
                      AM
                      Please respond to
                      "TechNet E-Mail
                      Forum."; Please
                      respond to Poh
                      Kong Hui






Hi Technetters,

I understand that the 'anti-tombstone' solder paste contained 0.4% silver.
Some people told me that the melting point is 179 deg.C and other said it
was 183 deg.C.

I am wandering which is correct.

And what about the percentage for the tin & lead, whether the tin makes up
63% of the alloy & the lead consists of 1.6%, or some other number.

Thanks.

Regards,
Poh

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