[Elecraft] Solder Alloys - Eutectic point

[G. Beat (W9GB)]

I really wish QST would reprint the excellent article that they had in the
late 1960's on solder alloys and why the 63/37 alloy mix has definite
advantages for PC board soldering.

Eutectic:  An alloy or solution having the lowest melting point (or freezing
point) possible.

Solder Alloy Temperature Chart
http://www.kester.com/alloy_temp_chart.html

Note that only 4 solder alloys on this chart have a "single point" melting
point (instead of a range).
Also notice that the more lead that is added beyond the 63/37 point - the
wider the melting range becomes.

Good soldering can successfully be accomplished with 60/40 (which I used
extensively in the 1970's until someone educated me with this chart).

Care must be taken to heat the solder joint at or beyond the high end of the
range (374 degrees F) and then not have the joint physically move until it
cools below the low end of the melting range (361 degrees F).  It does have
a nice finish.

I have been using 63/37 on all of my kits and work since, not a single cold
solder joint.

IF a higher temperature solder is required, lead free solder 96.5/3.5 silver
is available and provides high joint strength as a bonus.

From Kester's FAQ on their web page:  www.kester.com

      Sn63Pb37 This alloy is the tin-lead eutectic and is used in printed
circuit board manufacturing where temperature limitations are critical and
in applications where an extremely short melting range is required.
      Sn60Pb40 Similar to the tin-lead eutectic this alloy is used in
electrical work more specifically on single sided board technology. It is
also preferred for solder dipping operations as it imparts a smooth finish.

      Sn96.5Ag3.5 High temperature eutectic alloy. Used in applications
where high joint strength and a narrow process window are required.
      Sn62Pb36Ag02 Sn 62 as it is commonly referred to as, is widely used
for soldering silver coated ceramics and palladium silver substrates.


Greg
w9gb