Hi Steve and Werner
 
As the papers show, it was not a component solder joint  but a power bus 
connection between magnets that over heated and  failed and it appears evident 
that the quality of joining technology had a  likely role. (Your question 
relative to the suitability of high tin solder  as cryogenic temps is a good 
one, Steve... perhaps the copper serves to  stop tin pest?) 
 
_http://news.bbc.co.uk/2/hi/7632408.stm_ 
(http://news.bbc.co.uk/2/hi/7632408.stm)   
 
The link story from the BBC is consistent with what I was told by my  hosts 
when I visited CERN and the LHC the day after its dedication in October of  
last year (the failure was one month earlier) 
 
That said there are those who have reported event with a bit  more drama. 
(though it appears not to consider satellite mission  losses)     
 
_http://gizmodo.com/5090984/lhcs-21-million-single-joint-failure-is-the-most
-expensive-soldering-error-in-soldering-history_ 
(http://gizmodo.com/5090984/lhcs-21-million-single-joint-failure-is-the-most-expensive-soldering-error-
in-soldering-history) 
 
and then there is this... ;-) 
 
_http://geekapolis.fooyoh.com/geekapolis_gadgets_wishlist/4295243_ 
(http://geekapolis.fooyoh.com/geekapolis_gadgets_wishlist/4295243) 
 
Cheers, 
Joe
 
 
 
 
In a message dated 11/22/2009 11:58:29 A.M. Pacific Standard Time,  
[log in to unmask] writes:

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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