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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