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November 2009

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Subject:
From:
Mike Sewell <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Mike Sewell <[log in to unmask]>
Date:
Mon, 23 Nov 2009 09:59:23 -0600
Content-Type:
text/plain
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text/plain (210 lines)
Here's an old post from Mike Fenner, see below.  I remember tinning the leads Steve was referring to - if you tried a standard 63/37 pot at 300 C you would nearly dissolve the conductors while waiting for the insulation to burn off.  We set up a 30/70 pot and ran it around 350 C.  It worked well enough to get a cosmetically pretty joint after installation but we didn't section any of the bundles to see how much insulation was entrapped.

Regards,
Mike

Subject:	Re: Prepping Stranded Litz wire for soldering...
From:	Mike Fenner <[log in to unmask]>
Reply-To:	[log in to unmask]
Date:	Mon, 30 Jan 2006 17:01:42 -0000
Content-Type:	text/plain

The solder pot technique usually works OK on Litz wire. Also known as magnet
wire or self fluxing wire if you want to extend your search terms, but your
man hasn't given complete advice. 

It has to be done with a very hot pot and low tin content solder
[also usually single stranded wire, not flex.]

The low tin content  [30/70 or 40/60] is necessary to prevent the copper
wire necking in or even completely dissolving at the high (like 270-300 C)
temps necessary to get a good burn on the insulation, also cuts the drossing
down a bit. 



Regards 

Mike Fenner 
Indium Corporation 

T: + 44 1908 580 400 
M: + 44 7810 526 317 
F: + 44 1908 580 411 
E: [log in to unmask] 
W: www.indium.com 
Pb-free: www.Pb-Free.com

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Monday, November 23, 2009 9:28 AM
To: [log in to unmask]
Subject: Re: [TN] NTC Large Hadron Collider Restarts

Steve,

  You touched on an idem I am interested in, soldering to multi strand Litz
wire.

  Does anyone have, or point me toward, information about how different
insulation films can be reliably stripped to allow complete soldering of all
strands?

Thanks,
Bob Kondner

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of stephengregory5849
Sent: Sunday, November 22, 2009 10:08 PM
To: [log in to unmask]
Subject: Re: [TN] NTC Large Hadron Collider Restarts

You would think that there was due diligence when it came to the solder 
connections, but the temperatures that were referenced for soldering seemed 
a bit low from what I have learned from my limited experience soldering with

Sn96Ag4 solders. I've done some downhole soldering using both Sn96Ag4 
solderpaste, wire solder, and wave solder. 230-235 C peak temperatures seem 
a little on the low side to me. But what do I know?

I also have had a little experience trying to solder to probably the same 
kind of wire that was used. It probably was multi-stranded litz wire like 
was used in a transformer coil that I had to deal with:

 http://stevezeva.homestead.com/files/Coil_Solder_Joints.jpg

The coil came to us that supposedly had already been tinned and ready for 
soldering. But the strands still had coating all over them (it was some sort

of polyimide coating if I remember correctly), but it looked like it was 
ready to solder. As soon as we tried to solder it to the pads, strands of 
the wire started dewetting all over the place because the coating hadn't 
been completely removed, I personally worked on the solder joints that you 
see for at least a couple of hours with an exacto knife scrapping the 
coating away to get them looking like what you see in the photo. There is 
still a couple of areas that you can see a few strands that didn't wet...so 
I know what a PIA it is soldering stranded litz or magnet wire. BTW, this 
assembly was parylene coated before we did this rework.

Then digging a bit further about the choice of alloy and what's out there 
about tin pest in the low temperatures (liquid helium temperatures no less),

you come away with a lot of questions...

I wonder why they didn't chose regular ol' proven 63/37 solder? That's 
probably the biggest question I have...

Steve


----- Original Message ----- 
From: "Ioan Tempea" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Sunday, November 22, 2009 9:03 PM
Subject: Re: [TN] NTC Large Hadron Collider Restarts


Esteemed colleagues,

I have always considered the knowledge of Technet as my supreme source and I

have learned a lot!

But should we even think the people soldering the hadron had no idea what 
they were doing? Honestly, I am not worried a bit that just anybody got this

task. I bet big scientists were involved, even if we don't know them. Let's 
not forget the soldering bible has been written by a Dutch...

Regards,

Ioan Tempea, ing.
Ingénieur Principal de Fabrication / Senior Manufacturing Engineer
T | 450.967.7100 ext.244
E | [log in to unmask]
W | www.digico.cc

N'imprimer que si nécessaire - Print only if you must

-----Message d'origine-----
De : Steven Creswick [mailto:[log in to unmask]]
Envoyé : Sunday, November 22, 2009 7:46 PM
À : [log in to unmask]
Objet : Re: [TN] NTC Large Hadron Collider Restarts

Steve,

I admit that I should have taken more than a quick glance at the process
document which you presented, however, if the both parts of the joint have
been pre-tinned, AND the JOINT to be soldered is indeed brought up to 230C+,
why shouldn't the joint be reasonable?

My recollection is that the Sn96.5/Ag3.5 is a eutectic solder, melting at
221C, so the 230C is certainly a whole lot closer than I would prefer to run
with, but it should indeed have melted and bonded with the pre-tinned
surfaces.

Subsequent posts have discussed tin pest, etc.

My greatest apprehension is in regard to the stresses imposed in the joint
[any joint material] when transitioning from room temp to cryogenic and back
again.  I hope there is some serious stress/strain relief built into the
joint structure!

Werner, since you have had the opportunity to see the instrument to some
degree, can you provide insight as to the physical size and potential delta
length which may be involved in the soldered joint?

What are the physical sizes of the 'leads'.  Are they too large to join them
with a high-power ultrasonic welder, and do away with solder altogether??

Steve C

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