On Dec 3, 12:17, Marvin wrote:
> Philip.Belben_at_pgen.com wrote:
> >
> > Eh? Silver solder is certainly very nice, flows well, bonds to a lot
of metals,
> > etc., but isn't it usually _higher_ melting point? Conventional solder
melts at
> > around 450 F, I think. (Anyone have the exact figure?), silver solder
typically
> > at 600.
Yes, yes, no; see below...
> The melting point of solder varies depending on its composition. Eutectic
> solder (63/37) melts at about 361 degrees F and the melting point raises
as
> the percentage of either the lead or tin content raises.
That's not *exactly* true; the solidus point (the temperature at which it
begins to melt) remains almost exactly the same, but the liquidus point
rises. In between, though, the solder is rather pasty. That's great for
old-fashioned plumbing, but it's apt to produce dry joints in electronics,
so for practical purposes, the useful temperature rises just as Marvin
says.
For example, 40/60 solder has a liquidus point of 227C (440F) and 60/40 has
a liquidus point of 188C (370F). Adding certain other metals, especially
bismuth, lowers the melting point, though many other additives, such as
antimony, raise it. According to my Multicore Solder list, the recommended
bit temperature for 40/60 general-purpose electronics solder is 354C
(670F), and for 60/40 it's 308C (585F). Personally, I'm never that
precise; I just twist the setscrew on my Oryx TC irons until they work
right!
"Silver solder" comes in a variety of grades, the ones with the lowest
melting points are ArgoSwift and EasyFlo2 which melt at 600-610C
(1100-1130F, that's a dull red heat). EasyFlo2 is 42% silver, 17% copper,
16% zinc, and 25% cadmium. Most engineering silver solders are
silver+brass based like this. A few are silver-bronze (bronze being an
alloy of copper and tin).
The "silver-loaded" solder Tony and others mentioned is a soft solder
containing 62% tin, 36% lead, and 2% silver. It has a melting point of
179C (354F) and a recommended bit temperature of 300-310C (570-590F).
Other silver/tin/lead solders like Comsol (I bet Tony has come across that)
and LM5 are high-melting point soft solders, with a high lead content.
I've seen them used for fusible resistors and the like.
I expect this is at least four times as much as most of you ever wanted to
know about that silvery-grey stuff that holds the components on...
--
Pete Peter Turnbull
Dept. of Computer Science
University of York
Received on Fri Dec 03 1999 - 16:49:18 GMT