[TowerTalk] Solder For Connectors

[Jim Lux]

On 11/3/15 4:53 PM, John Reilly wrote:
> What are the advantages/disadvantages of using silver solder? I never
> have gotten a clear understanding when silver solder is appropriate.
>

Are you talking the no-lead tin/silver/copper alloys used for RoHS 
soldering, or "silver solder" as in "hard solder" for brazing?


Soldering is "join two metal things with a different metal of lower 
melting point", to distinguish from, say, welding, "join two metal 
things with more of the same metal"

Then there's usually a distinction between "soft solder" (historically 
using a tin/lead alloy with low melting point, although indium and 
bismuth are also used to lower the melting point) and "hard soldering" 
or "brazing" where the filler metal has a much higher MP (but still 
lower than the two things being joined).

In general "soft solder" isn't "structural": it's to make an electrical 
connection or to form a seal, but not to provide strength.  In fact, the 
softness of the solder is used in joints where there might be 
displacement (e.g. vacuum seals might be done with a soft solder) and 
something else takes the mechanical loads.  One does have to be careful 
about work hardening under loads.

Brazing, though, is usually used for something where a secure mechanical 
connection is needed.  There's a variety of silver containing alloys 
that have low-ish melting points (compared to steel and copper and 
brass) that also have decent mechanical properties, particularly under 
mechanical load/vibration. They also "stick well" to a lot of metals: 
one reason for brazing is when you want to join dissimilar metals 
together: You want to attach a copper widget to a steel structural 
member, and silver solder is your friend.