Re: [volt-nuts] low emf solder

[David]

On Sat, 29 Oct 2016 20:41:48 +0200, you wrote:

>On Sat, 29 Oct 2016 15:27:49 +0100
>"Dr. David Kirkby (Kirkby Microwave Ltd)"  
>wrote:
>
>> But if one could use copper as the bond wire, rather than gold which is
>> quite common, then it would give you very little thermal EMF
>
>Copper is more and more used for bonding wires.
>See:
>http://www.ti.com/lit/wp/sszy003/sszy003.pdf
>http://link.springer.com/article/10.1007/BF03214983 
>https://nepp.nasa.gov/files/26611/2015-370-Rutkowski-Final-Paper-NEPPweb-Copper-Wire-Bonds-TN26444.pdf
>
>But be aware, that the bond pad on the chip is still aluminium in most cases
>I don't know whether there is any process that uses copper bond pads at all.
>As far as I know, all of the relevant processes for analog designs (ie those 
>with node sizes over 130nm) still use aluminium interconnect only. IIRC the
>first node size that got copper interconnect was 65nm and about 10 years ago.
>
>...
>
>   Attila Kinali

Wide copper "straps" replaced gold and aluminum bond wires in high
performance power devices more than 10 years ago.  I think I first
heard about it from IRC (International Rectifier Corporation) for the
drain connection in TO-220 power MOSFETs to improve the Rds(on) which
was becoming limited by the package.  These days it is used with SO-8
and other packages as well.
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Re: [volt-nuts] low emf solder

[Florian Teply]

Am Sat, 29 Oct 2016 20:41:48 +0200
schrieb Attila Kinali :

> On Sat, 29 Oct 2016 15:27:49 +0100
> "Dr. David Kirkby (Kirkby Microwave Ltd)"
>  wrote:
> 
> > But if one could use copper as the bond wire, rather than gold
> > which is quite common, then it would give you very little thermal
> > EMF  
> 
> Copper is more and more used for bonding wires.
> See:
> http://www.ti.com/lit/wp/sszy003/sszy003.pdf
> http://link.springer.com/article/10.1007/BF03214983 
> https://nepp.nasa.gov/files/26611/2015-370-Rutkowski-Final-Paper-NEPPweb-Copper-Wire-Bonds-TN26444.pdf
> 
> But be aware, that the bond pad on the chip is still aluminium in
> most cases I don't know whether there is any process that uses copper
> bond pads at all. As far as I know, all of the relevant processes for
> analog designs (ie those with node sizes over 130nm) still use
> aluminium interconnect only. IIRC the first node size that got copper
> interconnect was 65nm and about 10 years ago.

I seem to recall that either IBM or AMD used copper already in 90nm,
but that's still in the same ballpark. And I don't see a reason why
one shouldn't use copper bondpads if the better part of the
metallization is copper already to begin with. But on the other hand
with the aluminium backend you mention for 130nm and larger node sizes,
you're also in for some interesting material combinations: a) the
aluminium isn't pure but usually has a copper content of between 0.5
and 1.5%. Then b) the vias are usually not aluminium but Tungsten or
something similar. Aluminium is only found at nodes starting from about
0.5 micron upwards, with 3 or less metallization layers. And finally,
as aluminium doesn't stick too well to Silicon dioxide, there will be
thin layers of, say, titanium or titanium nitride in between insulator
and metal. 
And please don't underestimate thermal gradients on chip. It's not
uncommon to see several tens of degrees difference in surface
temperature across even a small chip...

Best regards,
Florian
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Re: [volt-nuts] low emf solder

[Florian Teply]

Am Sun, 30 Oct 2016 01:05:56 -0500
schrieb David :

> Sounds more like copper free copper than oxygen free copper.

To be fair, one does not exclude the other. And nobody specified to what
the 100% is supposed to apply to. Being oxygen free does not necessarily
imply that it can't be a highly resistive magnetic alloy that by sheer
accident contains trace quantities of actual copper. Or does it
possibly mean that the cable is 100% pure, Copper and oxygen free? 100%
pure cable, nothing added to it...
> 
> On Sun, 30 Oct 2016 01:06:12 +, you wrote:
> 
> >Once you get past 99.99% purity funny things begin to happen...  I
> >have some 100% pure Cu oxygen free cable (says so right on the
> >jacket) made in China that is magnetic!  You can't do that with the
> >cheap stuff, now can you?  ;-)  Oh, and it is so pure that it has
> >three times the resistance of normal 99.99% pure American copper.
> >The US is so far behind China in the art of bogo-physics, I fear we
> >will never catch up.
> >  
> >>If you go for the oxygen-free variant you can get to 99.99% (don't
> >>ask me whether the audiophool grade is really that pure)  
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Re: [volt-nuts] low emf solder

[Andrea Baldoni]

On Sat, Oct 29, 2016 at 03:27:49PM +0100, Dr. David Kirkby (Kirkby Microwave 
Ltd) wrote:

> Perhaps the person who was making the measurements on the solder, could try
> making a thermocouple by welding two bits of wire taken from different
> sources. I guess the problem would be preventing any impurities entering
> the weld. A quick Google suggests one needs argon gas when welding copper.

Hello David.
I can test two different wires even without welding them, eventually.
This will not make a very durable thermocouple but if I clean them to avoid to
have a oxide layer, the result should be the same for the sake of measuring
thermal EMF.

I expect to have a very low signal to measure though. I must think to
experiment setup.

Best regards,
Andrea Baldoni
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Re: [volt-nuts] low emf solder

[John Phillips]

good one.

On Sat, Oct 29, 2016 at 11:05 PM, David  wrote:

> Sounds more like copper free copper than oxygen free copper.
>
> On Sun, 30 Oct 2016 01:06:12 +, you wrote:
>
> >Once you get past 99.99% purity funny things begin to happen...  I have
> some 100% pure Cu oxygen free cable (says so right on the jacket) made in
> China that is magnetic!  You can't do that with the cheap stuff, now can
> you?  ;-)  Oh, and it is so pure that it has three times the resistance of
> normal 99.99% pure American copper.  The US is so far behind China in the
> art of bogo-physics, I fear we will never catch up.
> >
> >>If you go for the oxygen-free variant you can get to 99.99% (don't ask
> me whether the
> >>audiophool grade is really that pure)
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>



-- 

*John Phillips*
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Re: [volt-nuts] low emf solder

[David]

Sounds more like copper free copper than oxygen free copper.

On Sun, 30 Oct 2016 01:06:12 +, you wrote:

>Once you get past 99.99% purity funny things begin to happen...  I have some 
>100% pure Cu oxygen free cable (says so right on the jacket) made in China 
>that is magnetic!  You can't do that with the cheap stuff, now can you?  ;-)  
>Oh, and it is so pure that it has three times the resistance of normal 99.99% 
>pure American copper.  The US is so far behind China in the art of 
>bogo-physics, I fear we will never catch up.
>
>>If you go for the oxygen-free variant you can get to 99.99% (don't ask me 
>>whether the
>>audiophool grade is really that pure)
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[volt-nuts] low emf solder

[Mark Sims]

Once you get past 99.99% purity funny things begin to happen...  I have some 
100% pure Cu oxygen free cable (says so right on the jacket) made in China that 
is magnetic!  You can't do that with the cheap stuff, now can you?  ;-)  Oh, 
and it is so pure that it has three times the resistance of normal 99.99% pure 
American copper.  The US is so far behind China in the art of bogo-physics, I 
fear we will never catch up.

--

If you go for the oxygen-free variant you can get to 99.99% (don't ask me 
whether the
audiophool grade is really that pure)
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Re: [volt-nuts] low emf solder

[John Allen]

Googling for "Things I Won't Work With" finds the article and others by Derek 
Lowe in his blog.

John K1AE

-Original Message-
From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of Mark Sims
Sent: Saturday, October 29, 2016 1:38 AM
To: volt-nuts@febo.com
Subject: [volt-nuts] low emf solder

I don't know if it the proper way but I used a very nice fume hood.   Measured 
the metals (high purity),  melted them in a quartz crucible,  stirred with a 
quartz rod,  and cast it in a ceramic block with a spiral pattern machined into 
it with a ball mill. You don't want to contaminate the mixture with other 
metals, etc.

That "Things I Won't Work With" article was about dimethyl cadmium, not 
metallic cadmium.  Reall Nasty Stuff.  Metallic cadmium and cadmium plating has 
been used for ages without killing too many people.  It's not something to take 
lightly, but I've had the pleasure of working around far worse things.

For even more extreme nastiness check out dimethyl mercury... one drop, goes 
through rubber gloves like they aren't there,  sure-fire rather horrible death. 
  Derek Lowe's "Things I Won't Work With" series is some of the best reading 
out there...  Unfortunately,  I don't think that he is still doing them.  His 
old web site has disappeared.

Just checked...  Derek is at it again after a two year hiatus...  woohoo!  He's 
my favorite chem-blogger.   Something makes me want to play with all the things 
he won't work with.
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Re: [volt-nuts] low emf solder

[Attila Kinali]

On Sat, 29 Oct 2016 15:27:49 +0100
"Dr. David Kirkby (Kirkby Microwave Ltd)"  
wrote:

> But if one could use copper as the bond wire, rather than gold which is
> quite common, then it would give you very little thermal EMF

Copper is more and more used for bonding wires.
See:
http://www.ti.com/lit/wp/sszy003/sszy003.pdf
http://link.springer.com/article/10.1007/BF03214983 
https://nepp.nasa.gov/files/26611/2015-370-Rutkowski-Final-Paper-NEPPweb-Copper-Wire-Bonds-TN26444.pdf

But be aware, that the bond pad on the chip is still aluminium in most cases
I don't know whether there is any process that uses copper bond pads at all.
As far as I know, all of the relevant processes for analog designs (ie those 
with node sizes over 130nm) still use aluminium interconnect only. IIRC the
first node size that got copper interconnect was 65nm and about 10 years ago.

> I would have thought any impurities in copper wire, would be quite small,
> as it would reduce the electrical conductivity. Whilst I accept one is not
> going to get 100.00 % pure copper, I would have thought
> the effect of any impurities at least an order of magnitude less than using
> solder. I'm only postulating this - I have no evidence to back it up, and
> have never studied the subject.

The normal copper wires you get are usually 99.9%. If you go for the
oxygen-free variant you can get to 99.99% (don't ask me whether the
audiophool grade is really that pure). I have no idea how much the EMF
of the impurities is.


Attila Kinali


-- 
Malek's Law:
Any simple idea will be worded in the most complicated way.
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[volt-nuts] low emf solder

[Mark Sims]

When making the CdSn solder you want to avoid contamination with other metals.  
It doesn't require much contamination to lose its magic foo powers.   So no 
metallic molds or tools used.

And what, no shaved cadmium with a Bordeaux garlic reduction?  Try it, it's 
delicious ;-)
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Re: [volt-nuts] low emf solder

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 29 October 2016 at 14:51, NeonJohn  wrote:

>
>
> On 10/28/2016 08:39 PM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
>
> > I wonder how practical it is to weld test leads, so there's no solder or
> > thermal EMF.
> >
> > I know that this will sound crazy, and probably is, but could one weld
> > components to a PCB?
>
> Yes indeed.  About 20 years ago I had a machine that made circuit board
> by routing tiny wires and spot welding them to the connection.  I can't
> for the life of me remember that process name.
>
> Only problem is, if you weld two different metals together, even copper
> with different compositions, you've still made a very rugged and durable
> thermocouple.
>
> John
>

But if one could use copper as the bond wire, rather than gold which is
quite common, then it would give you very little thermal EMF

I would have thought any impurities in copper wire, would be quite small,
as it would reduce the electrical conductivity. Whilst I accept one is not
going to get 100.00 % pure copper, I would have thought
the effect of any impurities at least an order of magnitude less than using
solder. I'm only postulating this - I have no evidence to back it up, and
have never studied the subject.

Perhaps the person who was making the measurements on the solder, could try
making a thermocouple by welding two bits of wire taken from different
sources. I guess the problem would be preventing any impurities entering
the weld. A quick Google suggests one needs argon gas when welding copper.

Dave
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Re: [volt-nuts] low emf solder

[NeonJohn]

On 10/28/2016 08:39 PM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:

> I wonder how practical it is to weld test leads, so there's no solder or
> thermal EMF.
> 
> I know that this will sound crazy, and probably is, but could one weld
> components to a PCB?

Yes indeed.  About 20 years ago I had a machine that made circuit board
by routing tiny wires and spot welding them to the connection.  I can't
for the life of me remember that process name.

Only problem is, if you weld two different metals together, even copper
with different compositions, you've still made a very rugged and durable
thermocouple.

John


-- 
John DeArmond
Tellico Plains, Occupied TN
http://www.tnduction.com<-- THE source for induction heaters
http://www.neon-john.com<-- email from here
http://www.johndearmond.com <-- Best damned Blog on the net
PGP key: wwwkeys.pgp.net: BCB68D77
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Re: [volt-nuts] low emf solder

[NeonJohn]

probably because they drowned some lab rats with solutions of the stuff.

As we say in the health-physics business, "the devil's in the dose".  If
I were working in a cad plating outfit, yeah, I'd check into what is
behind the IARC's somewhat arbitrary designation.

Making a small batch of cad solder at home?  Reasonable basic
precautions apply such as don't chew on the ingot.

John


On 10/28/2016 05:33 PM, Neville Michie wrote:
> LD50 is not the only consideration. From Wikipedia:
> 
> "The International Agency for Research on Cancer has classified
> cadmium and cadmium compounds as carcinogenic to humans."

-- 
John DeArmond
Tellico Plains, Occupied TN
http://www.tnduction.com<-- THE source for induction heaters
http://www.neon-john.com<-- email from here
http://www.johndearmond.com <-- Best damned Blog on the net
PGP key: wwwkeys.pgp.net: BCB68D77
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[volt-nuts] low emf solder

[Mark Sims]

I don't know if it the proper way but I used a very nice fume hood.   Measured 
the metals (high purity),  melted them in a quartz crucible,  stirred with a 
quartz rod,  and cast it in a ceramic block with a spiral pattern machined into 
it with a ball mill. You don't want to contaminate the mixture with other 
metals, etc.

That "Things I Won't Work With" article was about dimethyl cadmium, not 
metallic cadmium.  Reall Nasty Stuff.  Metallic cadmium and cadmium plating has 
been used for ages without killing too many people.  It's not something to take 
lightly, but I've had the pleasure of working around far worse things.

For even more extreme nastiness check out dimethyl mercury... one drop, goes 
through rubber gloves like they aren't there,  sure-fire rather horrible death. 
  Derek Lowe's "Things I Won't Work With" series is some of the best reading 
out there...  Unfortunately,  I don't think that he is still doing them.  His 
old web site has disappeared.

Just checked...  Derek is at it again after a two year hiatus...  woohoo!  He's 
my favorite chem-blogger.   Something makes me want to play with all the things 
he won't work with.
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Re: [volt-nuts] low emf solder

[David]

On Sat, 29 Oct 2016 01:39:12 +0100, you wrote:

>On 28 Oct 2016 15:25, "Juris L"  wrote:
>
>I wonder how practical it is to weld test leads, so there's no solder or
>thermal EMF.
>
>I know that this will sound crazy, and probably is, but could one weld
>components to a PCB?
>
>I don't even have the excuse of been drunk or taking drugs,  but I will
>risk ridicule for making the above comment!  Sometimes thinking out of the
>box is useful.
>
>Dave.

This can be done but whether it will help in the general case is
questionable because most parts do not use copper lead frames so the
thermocouple junction will be present whether soldered or welded.

On printed circuit boards, controlling temperature gradients and using
balanced circuits is usually sufficient.
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Re: [volt-nuts] low emf solder

[Scott Stobbe]

Typing on phone... If the bond wires are gold they still are dissimilar to
pcb copper, but if they were copper bond wires, thermal gradients would be
less of an issue.

On Friday, 28 October 2016, Scott Stobbe  wrote:

> "chip on board", not sure that it wouldnt help
>
> On Friday, 28 October 2016, Dr. David Kirkby (Kirkby Microwave Ltd) <
> drkir...@kirkbymicrowave.co.uk
> > wrote:
>
>> On 28 Oct 2016 15:25, "Juris L"  wrote:
>> >
>> > Found reference to optimal emf solder composition cadmium/tin alloy
>> > (70 %/30 %) in JJ array measurement article page 12.
>>
>> I wonder how practical it is to weld test leads, so there's no solder or
>> thermal EMF.
>>
>> I know that this will sound crazy, and probably is, but could one weld
>> components to a PCB?
>>
>> I don't even have the excuse of been drunk or taking drugs,  but I will
>> risk ridicule for making the above comment!  Sometimes thinking out of the
>> box is useful.
>>
>> Dave.
>> ___
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>> ailman/listinfo/volt-nuts
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>>
>
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Re: [volt-nuts] low emf solder

[Scott Stobbe]

"chip on board", not sure that it wouldnt help

On Friday, 28 October 2016, Dr. David Kirkby (Kirkby Microwave Ltd) <
drkir...@kirkbymicrowave.co.uk> wrote:

> On 28 Oct 2016 15:25, "Juris L" > wrote:
> >
> > Found reference to optimal emf solder composition cadmium/tin alloy
> > (70 %/30 %) in JJ array measurement article page 12.
>
> I wonder how practical it is to weld test leads, so there's no solder or
> thermal EMF.
>
> I know that this will sound crazy, and probably is, but could one weld
> components to a PCB?
>
> I don't even have the excuse of been drunk or taking drugs,  but I will
> risk ridicule for making the above comment!  Sometimes thinking out of the
> box is useful.
>
> Dave.
> ___
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Re: [volt-nuts] low emf solder

[Howard Davidson]

I note that  I weld thermocouples.
 hld 

Howard L. Davidson 
hl...@att.net

 
  From: Dr. David Kirkby (Kirkby Microwave Ltd) 
<drkir...@kirkbymicrowave.co.uk>
 To: Discussion of precise voltage measurement <volt-nuts@febo.com> 
 Sent: Friday, October 28, 2016 5:39 PM
 Subject: Re: [volt-nuts] low emf solder
   
On 28 Oct 2016 15:25, "Juris L" <juri...@gmail.com> wrote:
>
> Found reference to optimal emf solder composition cadmium/tin alloy
> (70 %/30 %) in JJ array measurement article page 12.

I wonder how practical it is to weld test leads, so there's no solder or
thermal EMF.

I know that this will sound crazy, and probably is, but could one weld
components to a PCB?

I don't even have the excuse of been drunk or taking drugs,  but I will
risk ridicule for making the above comment!  Sometimes thinking out of the
box is useful.

Dave.
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Re: [volt-nuts] low emf solder

[Bruce Griffiths]

Laser welding should work for either similar or dissimilar materials.At one 
time microwire PCBs  used stainless steel  wires were welded to stainless lands.
Bruce  

On Saturday, 29 October 2016 1:39 PM, Dr. David Kirkby (Kirkby Microwave 
Ltd)  wrote:
 

 On 28 Oct 2016 15:25, "Juris L"  wrote:
>
> Found reference to optimal emf solder composition cadmium/tin alloy
> (70 %/30 %) in JJ array measurement article page 12.

I wonder how practical it is to weld test leads, so there's no solder or
thermal EMF.

I know that this will sound crazy, and probably is, but could one weld
components to a PCB?

I don't even have the excuse of been drunk or taking drugs,  but I will
risk ridicule for making the above comment!  Sometimes thinking out of the
box is useful.

Dave.
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Re: [volt-nuts] low emf solder

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 28 Oct 2016 15:25, "Juris L"  wrote:
>
> Found reference to optimal emf solder composition cadmium/tin alloy
> (70 %/30 %) in JJ array measurement article page 12.

I wonder how practical it is to weld test leads, so there's no solder or
thermal EMF.

I know that this will sound crazy, and probably is, but could one weld
components to a PCB?

I don't even have the excuse of been drunk or taking drugs,  but I will
risk ridicule for making the above comment!  Sometimes thinking out of the
box is useful.

Dave.
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Re: [volt-nuts] low emf solder

[Poul-Henning Kamp]

In message , NeonJohn 
writes:

>Let's don't get carried away with cadmium toxicity.  Yes, it is toxic is
>sufficient dose but the LD50 dose for Cd is  750 mg/kg while the value
>for lead is around 450mg/kg.

Read how a professional chemist describes cadmium:

http://blogs.sciencemag.org/pipeline/archives/2013/05/08/things_i_wont_work_with_dimethylcadmium

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [volt-nuts] low emf solder

[Neville Michie]

LD50 is not the only consideration. From Wikipedia:

"The International Agency for Research on Cancer has classified cadmium and 
cadmium compounds as carcinogenic to humans."

FWIW

Neville Michie


> On 29 Oct 2016, at 8:09 AM, NeonJohn  wrote:
> 
> Let's don't get carried away with cadmium toxicity.  Yes, it is toxic is
> sufficient dose but the LD50 dose for Cd is  750 mg/kg while the value
> for lead is around 450mg/kg.
> 
> As far as dumping it in a solder pot, that works just fine for me.  It's
> cheaper to buy 50/50 plumber's bar solder and then add the appropriate
> amount of lead to get to the eutectic point.
> 
> One should also realize that cad-plated hardware is still available.  I
> get mine from McMaster-Carr.
> 
> John
> 
> 
> On 10/28/2016 12:39 PM, ed breya wrote:
>> I would recommend against trying to use cadmium - it's very toxic, which
>> is why Cd-based solders are rare nowadays. They are probably still made,
>> but for lab or industrial use with proper handling. If you try to alloy
>> it with Sn yourself without proper handling, you could get poisoned. You
>> can't just throw the ingredients in a solder pot and expect good results.
>> 
>> Ed
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> 
> -- 
> John DeArmond
> Tellico Plains, Occupied TN
> http://www.tnduction.com<-- THE source for induction heaters
> http://www.neon-john.com<-- email from here
> http://www.johndearmond.com <-- Best damned Blog on the net
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Re: [volt-nuts] low emf solder

[NeonJohn]

Let's don't get carried away with cadmium toxicity.  Yes, it is toxic is
sufficient dose but the LD50 dose for Cd is  750 mg/kg while the value
for lead is around 450mg/kg.

As far as dumping it in a solder pot, that works just fine for me.  It's
cheaper to buy 50/50 plumber's bar solder and then add the appropriate
amount of lead to get to the eutectic point.

One should also realize that cad-plated hardware is still available.  I
get mine from McMaster-Carr.

John


On 10/28/2016 12:39 PM, ed breya wrote:
> I would recommend against trying to use cadmium - it's very toxic, which
> is why Cd-based solders are rare nowadays. They are probably still made,
> but for lab or industrial use with proper handling. If you try to alloy
> it with Sn yourself without proper handling, you could get poisoned. You
> can't just throw the ingredients in a solder pot and expect good results.
> 
> Ed
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> and follow the instructions there.
> 

-- 
John DeArmond
Tellico Plains, Occupied TN
http://www.tnduction.com<-- THE source for induction heaters
http://www.neon-john.com<-- email from here
http://www.johndearmond.com <-- Best damned Blog on the net
PGP key: wwwkeys.pgp.net: BCB68D77
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[volt-nuts] low emf solder

[Mark Sims]

A few years back I whipped up a batch of Cd/Sn solder...  but I had access to 
the proper equipment to do it safely.  And no, you can't have any!
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Re: [volt-nuts] low emf solder

[ed breya]

I would recommend against trying to use cadmium - it's very toxic, which 
is why Cd-based solders are rare nowadays. They are probably still made, 
but for lab or industrial use with proper handling. If you try to alloy 
it with Sn yourself without proper handling, you could get poisoned. You 
can't just throw the ingredients in a solder pot and expect good results.


Ed
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[volt-nuts] low emf solder

[Juris L]

Found reference to optimal emf solder composition cadmium/tin alloy
(70 %/30 %) in JJ array measurement article page 12.

www.bipm.org/utils/common/pdf/rapportBIPM/2011/05.pdf

Quick look at ebay show 1/4 kg of pure cadmium cost 10$ (item 111333082639),
so you can make quite a lot of solder for cheap ...

Also interesting way to thermally anchor interconnection leads to
copper block in page 11.

J.
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[volt-nuts] Low EMF solder

[Dave M]

Please excuse me for asking this... I'm sure it's been covered before, but 
without an easy way to search the archives, here goes.

I'm repairing a couple of old Holt 323A Audio Voltage Standards, trying to 
make one good one out of two.  These instruments used to have small hanks of 
special low EMF solder to use on sensitive areas, but they have long since 
vanished from these units.  I've tried using Sn-Pb solders, but the units go 
into a tizzy when I use it.

Does anyone know of a source where I could buy a few ounces of the solder? 
I think it's a Tin-Cadmium formula, but I guess that because of the Cadmium 
content, it's pretty much unobtanium now.  I'm sure that another formula 
must exist that is currently being manufactured, but they want to sell a 
bunch, not just a few ounces.

Suggestions?

Dave M 
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