Best Solder [Lead free] for vacuum application and other questions

[msimunic]

I've noticed one thread about "Best Solder" but My question is different.
I'm doing a small research about solder alloy application in satellite electronics.
Also, I need to buy a solder for My self at home, ground level :-). For My self, I prefer Lead-free solder if not to expensive.

From My experience thin wires ie. 0.5 mm are to thin for soldering SOIC, USB connectors and similar size IC pins.
You must put lengthy piece of wire to make a solder joint. My be due to cheap solder wire, but also there was effect of not wetting enough.
I've worked with Fluitin Lead-free Solder wire (don't know exact alloy) - It was OK, it feels harder to solder and less wetting than with leaded Sn60/Pb40 solder wire (Fluitin, also).
It was some time before, so I forgot about wire dimensions and alloys. Fluitin lead-free may be 1mm thick Sn95.3/Ag4/Cu0.7 wire, but I'm not sure.
 
I've noticed the erosion that Sn60/Pb40 solder makes on soldering tips. I've worked with some brand name (like Fluitin or Chemtronics, but I'm not not sure which).
So first question is:
1) Does anybody know of brand which have solder wire (Sn60/Pb40) that doesn't make such erosion on solder tips?

I would prefer Lead-free solder. I noticed similar alloys - Sn95.3/Ag4/Cu0.7 and Sn95.5/Ag4/Cu0.5 and Sn95/Ag4/Cu1. The later Sn95/Ag4/Cu1 tends to be more expensive.
2) Could somebody tell about experience with those alloys? Is there any difference?

I know about solder dendrite forming/growth in vacuum and solder fatigue due to temperature cycling.
3) Which Solder alloys are preferred for vacuum applications. Especially for space applications, ie. Satellite electronics.
4) Which Solder alloys are preferred for durability due to temperature cycling?

Thanks.

[tooki]

I don't have any experience with vacuum/satellite, so I can't address those specifics. But in general:

- In terms of the metal alloy, leaded solder is less damaging to the soldering iron tip than lead-free. If your leaded solder is causing more erosion, it's because of it having an aggressive flux.

- Leaded solder wets better than lead-free. Adjusting the temperature and using added flux become more important with lead-free.

- Thin solder (like 0.5mm) lets you apply solder slowly, to prevent you from applying excess solder. If you want to add solder faster, take two strands of the thin solder and twist them together. (Of course, thin solder costs more than thick solder, so if you constantly need thick solder, then you should buy some.)

[2N3055]

Look for nasa whitepapers on soldering reliabilty.  Generaly, leaded solder is less brittle and was space certified by nasa in the day. But it's not that simple. Google space and solder and sift through results.

[David Hess]

1) Does anybody know of brand which have solder wire (Sn60/Pb40) that doesn't make such erosion on solder tips?

It is the tin in the solder which is the problem.  Lead free alloys which include more tin dissolve the soldering iron tip and copper more quickly.  But this is not a problem for a properly cared for iron plated soldering iron tip.

I would prefer Lead-free solder. I noticed similar alloys - Sn95.3/Ag4/Cu0.7 and Sn95.5/Ag4/Cu0.5 and Sn95/Ag4/Cu1. The later Sn95/Ag4/Cu1 tends to be more expensive.
2) Could somebody tell about experience with those alloys? Is there any difference?

In practice the SnAgCu alloys all perform about the same as a general purpose Sn60/Pb40 replacement albeit while not performing as well.  One of them, I forget which, is eutectic and patented.

I know about solder dendrite forming/growth in vacuum and solder fatigue due to temperature cycling.
3) Which Solder alloys are preferred for vacuum applications. Especially for space applications, ie. Satellite electronics.
4) Which Solder alloys are preferred for durability due to temperature cycling?

NASA has published some articles on this subject.  Dendrite growth is a problem with some tin based lead free solders and a good reason to stick with Sn60/Pb40.

[stj]

the usual classic mistake here,
wetting etc is not down to the metal composition but the type and percentage of flux.

and i'll warn you now, if you go down the halide-free route you wont be happy - halide is needed to solder to stuff like brass(pins,tabs etc)

--
btw, space is not a vacuum, it's a low pressure mixture of gasses with clouds of fine dust suspended in it.
dont think something going into space wont need to be insulated/protected.