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November 2009

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Subject:
From:
Werner Engelmaier <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Werner Engelmaier <[log in to unmask]>
Date:
Sun, 22 Nov 2009 16:27:30 -0500
Content-Type:
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Hi Stephen,
A very curious choice indeed—did/do they have anybody that knows 
something about soldering?
A further worry is, that at 4% Ag the concentration of SnAg-IMC 
cyrystal plateletts is high enough to cause Ag-embrittlement of the SJs.
Werner

-----Original Message-----
From: stephengregory5849 <[log in to unmask]>
To: [log in to unmask]
Sent: Sun, Nov 22, 2009 4:08 pm
Subject: Re: [TN] NTC Large Hadron Collider Restarts

Hi Werner,

Of course you're correct. I've always referred to Sn96Ag4 solder 
incorrectly as "Sn96".

Also something that I did not think about until you brought it up, is 
the -40C environment. Tin pest starts to occur at temperatures below 
13.2C, and what I found is that silver really isn't the best metal to 
add to prevent tin pest from occuring. Even then it needs to be at 
levels greater than 5% to be effective. See:

http://www.indium.com/images/blogs/drlasky/files/TinPestPaper0723Final.pdf

I wonder why they chose Sn96Ag4 solder to make the solder connections?

Steve
  ----- Original Message -----
  From: Werner Engelmaier
  To: [log in to unmask] ; [log in to unmask]
  Sent: Sunday, November 22, 2009 2:56 PM
  Subject: Re: [TN] NTC Large Hadron Collider Restarts


  Hi Stephen,
  Thanks for the info.
  Please do not call this solder Sn96—very misleading; it is Sn96Ag4.
   Your concerns are valid; 230C is just above the Liquidus (the solidus 
is 218C) for this solder and heating the SJ "up to 230C" [THPCH183 
reference] or "should be held at 235C for one minute" [yksdbt 
reference] is less than reassuring for getting consistent quality SJs.
   I expressed concerns a year ago when this first broke, that this SJ 
may be only the first failure of many to occur somewhat later. Nothing 
is said about any reliability assurance/design to make sure cooling to 
-40C is not severely detrimental to this arrangement.
  Werner





  -----Original Message-----
  From: stephengregory5849 <[log in to unmask]>
  To: [log in to unmask]
  Sent: Sun, Nov 22, 2009 1:49 pm
  Subject: [TN] NTC Large Hadron Collider Restarts


Some of you may have heard that the LHC (Large Hadron Collider) has 
restarted
after shutting down last year because of a reported bad solder joint.

I have wondered what kind of solder was used for the connections of the
superconducting cables that failed in the LHC, I think I know 
now...SN96. I also
think I found out how they soldered them. Resistance soldering. Here's 
the
procedure:

http://tinyurl.com/yksdbt6

and another reference:

http://accelconf.web.cern.ch/AccelConf/e06/PAPERS/THPCH183.PDF

What bothers me in both of them, is that they are only heating the 
connections
up to 230 C. and caution not to exceed 240 C. Is that high enough using 
SN96 to
form a good metallurgical bond?

Steve

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