Yes pure or sometimes very high In content alloys can be made to "wet" non-
metallics like Alumina but this is not what we think of as a soldering
application where the joining alloy diffuses into the work surface. It's
more of a mechanical action and the conditions necessary are not present in
a true soldering operation, i.e. messy (in this context) flux will stop it.
.
Yes in soldering terms copper is to indium much like gold is to tin. Indium
can make hard intermetallics with Au. In will diffuse into Au even in the
solid state for as long as either metal is in the presence of the other. The
hard intermetallics formed at time of soldering and in service give a
bondline which is the exact opposite of the soft flexibility that made In
desirable in the first place.
.
Yes you need an isolating coating if soldering to copper to prevent this
from happening. Nickel is good, but silver can dissolve on soldering and so
is not an unqualified first choice. (Note when using In as a TIM and where
the Cu and In are naturally oxidised/tarnished on presentation this is not
normally a problem).
.
You also need to consider your flux choice. In is like slowed down tin in
soldering so you need a flux which may have to "hang" around a bit and/or
has low activation temperature  if required and is halide free as In is
susceptible to halides.

So refer to my original answer - you need to go though all your process and
in service parameters with your supplier. 
Don't forget I also said that Sn/Pb could be OK. So that would be the first
thing to look at.

There is a mound of stuff on thermal cycling alloys to help form an opinion
on best alloy choice. A lot of this generated by the need to document
properties of Sn/Pb versus Pb free alloys. I say help as the data is on test
pieces and not your actual assembly. When choosing an alloy it is easy to
eliminate the ones that definitely won't work. This elimination process will
result- in an ideal world- with one survivor.  In reality with more than
one. So as said above you need to go through the surviving candidates to
pick the most likely to succeed in your app. Not something that can really
be done by serial emailing in this forum unfortunately.

Regards

Mike

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: Thursday, June 04, 2015 9:12 PM
To: [log in to unmask]
Subject: Re: [TN] Solder Alloy SnIn - Working Environmental Conditions:
-100°C to +100°C

Silver isn't generally the first thing I think of when I want a diffusion
barrier, but I'll let those with more experience in this area teach us
something! Mike?

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ricardo Moncaglieri
Sent: Thursday, June 04, 2015 4:05 PM
To: [log in to unmask]
Subject: Re: [TN] Solder Alloy SnIn - Working Environmental Conditions:
-100°C to +100°C

What about using Ag plating in place of Ni? Do you have any background?


>>> Ricardo Moncaglieri <[log in to unmask]> 04/06/2015 08:24
>>>
As per last comments better alloy should be InPb alloy always apllied over
Ni finish. Isnt it?
Do you know an specific paper/site to pick up cryogenic apps data (InPb)?
All your advise comes good. Appreciate it so long.
Will put a glance in the David Hillman recomended book too.  

>>> Wayne Thayer <[log in to unmask]> 03/06/2015 17:51 >>>
And don't forget about the potential for nasty InCu intermetallics! If you
go with indium, nickel plate everything first.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: Wednesday, June 03, 2015 4:41 PM
To: [log in to unmask]
Subject: Re: [TN] Solder Alloy SnIn - Working Environmental
Conditions:
-100°C to +100°C

In/Sn solidus of 118C is almost certainly too low for 100C working
environment and there is not much benefit in ductility from this alloy at
the other end.
Probably Sn63 might cope in fact, but if you have large TEC mismatch, or
multiple cycles and other it depends stuff you might wish to look at an
In/Pb alloy. These are good for cryogenic apps so plenty in hand and you
have choice of MPs at other end of use scale. 
No benefit is without a cost though so you may have some surface finish
issues. To quote myself" it's never just the melting point" when it comes to
alloy choice. Discuss with your specialist supplier.

--
Regards 

Mike Fenner
BS&P
M: +44 [0] 7810 526 317
T: +44 [0] 1865 522 663

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ricardo Moncaglieri
Sent: Tuesday, June 02, 2015 10:18 PM
To: [log in to unmask]
Subject: [TN] Solder Alloy SnIn - Working Environmental Conditions:
-100°C
to +100°C

Dear Colleagues,
Have to deploy a process and its qualification in order to perform
electrical connections which will be working under temperature variations in
the range of -100°C to +100°C (space application).
We are pointing to SnIn solder alloy.
We are just now starting  our investigation in our first steps.
Will be invaluable some advise as per your background so as directing me to
some std and/or paper about best applicable solder alloy and its
qualification method.
Being grateful in advance.
brgds, Ricardo Moncaglieri



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