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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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