Wondering the guys on WEEE board selected the solder? Can't resist the "resistive soldering". Good to know that failure is occur at ground level (on earth). What happen if it is in the sky? Whew!
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----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Sun Nov 22 16:27:30 2009
Subject: Re: [TN] NTC Large Hadron Collider Restarts
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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