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Date: | Fri, 22 Nov 96 12:08:06 cst |
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Hi TechNet!
Oh boy, another question for the metallurgists!! A eutectic
transformation is when a liquid converts to two or more intimately
mixed solids! Many metals have eutectic points on their phase
diagrams. The reason to use a eutectic alloy of solder is that in
manufacturing you can use the convenient liquid/solid switch as the
on/off switch to facilitate handling, processing etc. The true
eutectic for tin/lead is 61.9%tin/38.1%lead (183C)- everyone calls
63/37 or 60/40 eutectic but they are really near eutectic alloys. As
for 62Sn, 36Pb, and 2Ag there is some literature published that shows
the alloy is better in reliability than 63/37 - there is also data
that says 62Sn, 36Pb, and 2Ag is no different than 63/37 so you will
have to review the data to form an opinion. When chip capacitors
didn't have barrier metals the 62Sn/36Pb/2Ag was used to help slow
down leaching of the PdAg alloy off the chip capacitor end cap.
Barrier metals are used by most chip capacitor fabricators today so
leaching isn't an issue any more. Your "pasty" range of the 62Sn,
36Pb, and 2Ag alloy isn't very big so I don't think any preheater
adjustments are necessary. Hope this is helpful.
Dave Hillman
Rockwell Collins
[log in to unmask]
______________________________ Reply Separator _________________________________
Subject: Sub: Solder Paste Plastic or Eutectic
Author: [log in to unmask] at ccmgw1
Date: 11/21/96 4:49 PM
Question:
If I have a solder paste that is 62Sn, 36Pb, and 2Ag, is
this a Eutectic or Plastic range solder paste? 63Sn/37Pb is
a Eutectic solder with a freeze point at 361 degrees "F".
I am using a ESP paste at the above mix. The range of this
solder is 354 - 372 degrees. If so it would seem to be a
plastic solder. If this is true then I need to readjust my
preheat temperatures at Wave Solder to compensate for the
354 degree low end of the solder paste to prevent reflow.
Is this paste Eutectic or Plastic? Has anyone experienced
this? Do I need a 62/36/2 paste like this? Why would a
regular 63/37 paste work?
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