bz wrote in
98.139:

63/37: melts between 180-185°C
60/40: melts between 183-190°C
50/50: melts between 185-215°C

I'm not aware of any soldering process that is able to control
temperature so closely as to not melt one, while melting another of
those formulations. Can you elaborate?

When I worked as a process engineer for Sprague Electric Co, in the
early 70's, making capacitors and resistors, we used 95/5 solder, I
think it was tin/lead with a small amount of silver, to assemble the
capacitors and resistors.

One reason for that choice was so that the parts would withstand
normal 60/40 soldering when boards were assembled.

Like you, I have some doubts about the kind of close control that
would be needed to use mixes as close as the ones given.



I doubt it can be that accurately done. I use various indium based solders
for making small assemblies of optics and electronics when I want to get
different melting points, and you need well defined narrow ranges for ech
solder, with at least 10 degrees apart between each rangem ideally, because
an assembly might easily see several degrees variation unless you're
prepared to control the conditions with expensive rigour and to wait a long
time for equlibrium to settle each time you change the temperature. Two
solders wth overlapping ranges for melting would be useless.