Lead-Free Solder: Weird Behavior

[Daniel Haude]

Hello,

I've been trying to solder wires to copper-plated piezo actuators using
lead-free electronics solder. It turns out that within a fraction of a
second I get something that resembles a solder joint, but then the solder
immediately retracts to other parts of the surface, leaving behind a
dullish-grey area that won't wet any more no matter what I try.

I've been soldering piezos a lot, and I've been using lead-free solder a
lot (the stuff used for plumbing; it has a higher melting point than the
electronics stuff but is otherwise a similar alloy). Only I've been using
nickel- and gold-over-nickel plated piezos which solder like a charm.

Problem is that in my application I can't have lead, and I can't have
magnetic material.

I've tried to scrape off that grey layer, but it seems like I hit the
piezo material right away. I can't tell if I have any copper left because
the copper is only some three microns in the first place.

Of course the stuff solders as expected with lead solder (which, however,
won't stick to the surface spoilt by the lead-free stuff).

Could it be that the lead-free solder dissolves copper to form some
un-solderable alloy? Sounds odd since the solder alloy contains some
copper itself.

The flux is not the culprit; I'm using both resin and a phosphorous
acid based stuff, and both don't affect soldering with lead-containing
solder.

Any hints appreciated,
--Daniel

 

[Roger Hamlett]

Hello,

I've been trying to solder wires to copper-plated piezo actuators using
lead-free electronics solder. It turns out that within a fraction of a
second I get something that resembles a solder joint, but then the
solder
immediately retracts to other parts of the surface, leaving behind a
dullish-grey area that won't wet any more no matter what I try.

I've been soldering piezos a lot, and I've been using lead-free solder a
lot (the stuff used for plumbing; it has a higher melting point than the
electronics stuff but is otherwise a similar alloy). Only I've been
using
nickel- and gold-over-nickel plated piezos which solder like a charm.

Problem is that in my application I can't have lead, and I can't have
magnetic material.

I've tried to scrape off that grey layer, but it seems like I hit the
piezo material right away. I can't tell if I have any copper left
because
the copper is only some three microns in the first place.

Of course the stuff solders as expected with lead solder (which,
however,
won't stick to the surface spoilt by the lead-free stuff).

Could it be that the lead-free solder dissolves copper to form some
un-solderable alloy? Sounds odd since the solder alloy contains some
copper itself.

The flux is not the culprit; I'm using both resin and a phosphorous
acid based stuff, and both don't affect soldering with lead-containing
solder.

Any hints appreciated,
--Daniel

Are you using a different iron?.
Lead free solders, except special varieties designed to handle lead
contaimination, hate having any lead present. if you are using an iron
that still has a tinned coating on the tip from using a lead based solder,
it could give the behaviour you are seeing...

Best Wishes

 

[John Woodgate]

I read in sci.electronics.design that Daniel Haude

Could it be that the lead-free solder dissolves copper to form some
un-solderable alloy? Sounds odd since the solder alloy contains some
copper itself.

Yes, your experience seems to indicate that. But it may not be just
Cu/Pb. I doubt that the Cu is plated directly on to the piezo material,
and if there is, for example, a Ni interlayer there, the possibility of
getting a non-wetting alloy is much greater. Especially if you are using
phosphoric acid.

Try using lead-free solder made for **electronics**, not the Sn/Cu stuff
used for plumbing.

 

[John Larkin]

Hello,

I've been trying to solder wires to copper-plated piezo actuators using
lead-free electronics solder. It turns out that within a fraction of a
second I get something that resembles a solder joint, but then the solder
immediately retracts to other parts of the surface, leaving behind a
dullish-grey area that won't wet any more no matter what I try.

I've been soldering piezos a lot, and I've been using lead-free solder a
lot (the stuff used for plumbing; it has a higher melting point than the
electronics stuff but is otherwise a similar alloy). Only I've been using
nickel- and gold-over-nickel plated piezos which solder like a charm.

Problem is that in my application I can't have lead, and I can't have
magnetic material.

I've tried to scrape off that grey layer, but it seems like I hit the
piezo material right away. I can't tell if I have any copper left because
the copper is only some three microns in the first place.

Of course the stuff solders as expected with lead solder (which, however,
won't stick to the surface spoilt by the lead-free stuff).

Could it be that the lead-free solder dissolves copper to form some
un-solderable alloy? Sounds odd since the solder alloy contains some
copper itself.

It probably just dissolved all the copper away, then beaded up.

Considered conductive epoxy?

John

 

[John Popelish]

Hello,

I've been trying to solder wires to copper-plated piezo actuators using
lead-free electronics solder. It turns out that within a fraction of a
second I get something that resembles a solder joint, but then the solder
immediately retracts to other parts of the surface, leaving behind a
dullish-grey area that won't wet any more no matter what I try.

I've been soldering piezos a lot, and I've been using lead-free solder a
lot (the stuff used for plumbing; it has a higher melting point than the
electronics stuff but is otherwise a similar alloy). Only I've been using
nickel- and gold-over-nickel plated piezos which solder like a charm.

Problem is that in my application I can't have lead, and I can't have
magnetic material.

I've tried to scrape off that grey layer, but it seems like I hit the
piezo material right away. I can't tell if I have any copper left because
the copper is only some three microns in the first place.

Of course the stuff solders as expected with lead solder (which, however,
won't stick to the surface spoilt by the lead-free stuff).

Could it be that the lead-free solder dissolves copper to form some
un-solderable alloy? Sounds odd since the solder alloy contains some
copper itself.

The flux is not the culprit; I'm using both resin and a phosphorous
acid based stuff, and both don't affect soldering with lead-containing
solder.

Any hints appreciated,
--Daniel

I had something very similar happen when I tried to solder positive
tempco thermistor pellets between two brass sheets. I was using tin
lead solder, and the result was similar to what you are getting. The
extremely thin silver metalization layer was simply dissolving in the
solder and leaving me with an ummetalized die. In my case, it was not
necessary to eliminate lead, so the solution (pardon the pun) was to
use 2% silver solder, minimum temperature and soldering time.

Evidently your metalization layer is quite soluble (given the
temperature and time) in the solder you are using. There is some low
temperature tin bismuth solder that might work better.

 

[Tim Wescott]

I had something very similar happen when I tried to solder positive
tempco thermistor pellets between two brass sheets. I was using tin
lead solder, and the result was similar to what you are getting. The
extremely thin silver metalization layer was simply dissolving in the
solder and leaving me with an ummetalized die. In my case, it was not
necessary to eliminate lead, so the solution (pardon the pun) was to
use 2% silver solder, minimum temperature and soldering time.

Evidently your metalization layer is quite soluble (given the
temperature and time) in the solder you are using. There is some low
temperature tin bismuth solder that might work better.

You can (or could) get tin-lead solder that came pre-saturated with
copper, to prevent the solder from dissolving your tip or other valuable
things -- is it possible to get this same thing in lead-free solder?

 

[John Woodgate]

I read in sci.electronics.design that John Popelish <[email protected]>

There is some low temperature tin bismuth solder that might work
better.

Back in the Dark Ages, before 1930, people used Woods Metal to fix
galena crystals for crystal receivers into their holders. maybe it
should make a come-back. However, it's 25% Pb, so no deal....

 

[Robert Baer]

Hello,

I've been trying to solder wires to copper-plated piezo actuators using
lead-free electronics solder. It turns out that within a fraction of a
second I get something that resembles a solder joint, but then the solder
immediately retracts to other parts of the surface, leaving behind a
dullish-grey area that won't wet any more no matter what I try.

I've been soldering piezos a lot, and I've been using lead-free solder a
lot (the stuff used for plumbing; it has a higher melting point than the
electronics stuff but is otherwise a similar alloy). Only I've been using
nickel- and gold-over-nickel plated piezos which solder like a charm.

Problem is that in my application I can't have lead, and I can't have
magnetic material.

I've tried to scrape off that grey layer, but it seems like I hit the
piezo material right away. I can't tell if I have any copper left because
the copper is only some three microns in the first place.

Of course the stuff solders as expected with lead solder (which, however,
won't stick to the surface spoilt by the lead-free stuff).

Could it be that the lead-free solder dissolves copper to form some
un-solderable alloy? Sounds odd since the solder alloy contains some
copper itself.

The flux is not the culprit; I'm using both resin and a phosphorous
acid based stuff, and both don't affect soldering with lead-containing
solder.

Any hints appreciated,
--Daniel

Firstly, it is known that there is a problem with (standard tin-lead)
solder on gold.
It works very well, and looks super when done.
However, as time goes on, the solder will seperate from the gold as
if nothing was done.
The solution to this is a standard practice: slobber solder on,
remove and sloober again - until all the damn gold is leached from the
surface; *then* solder the connection.

Secondly: plumbers solder is not lead free, and usually uses ACID
(!!); there are numerous strong recommendations against use of plumbers
solder. And it is *not* considered fit for electronics use.

There are numerous *electronic* lead-free solders:
* Sn 95.5, Ag 3.8, Cu 0.7 - MP 217C / 423 F; adopted by NEMI adn many
high volume consumer OEMs
* Sn 96.5, Ag 3.5 - MP 221C / 430F
* Sn 95, Sb 5 - MP 232C / 450F
Of all of these, i would strongly recommend the first, because it
does have copper and would be less likely to leach copper from your parts.
And it is clear from your description that leaching is the primary
culprit.

 

[Robert Baer]

You can (or could) get tin-lead solder that came pre-saturated with
copper, to prevent the solder from dissolving your tip or other valuable
things -- is it possible to get this same thing in lead-free solder?

Yes; see my earlier posting in this thread.

 

[budgie]

Back in the Dark Ages, before 1930, people used Woods Metal to fix
galena crystals for crystal receivers into their holders. maybe it
should make a come-back.

It also used to be used for "trick" teaspoons that melted when you tried to stir
your hot cuppa.

However, it's 25% Pb, so no deal....

That didn't stop them then ;-)

 

[Daniel Haude]

On Mon, 21 Mar 2005 08:34:12 -0800,

It probably just dissolved all the copper away, then beaded up.

Considered conductive epoxy?

Yes, I'd use H20E. But this will take ages to do because I can't do all
the joints at the same time. Grrr. I'm reconsidering tin-lead solder, but
since this is a ultrahigh vacuum device lead is some sort of a no-no (too
high vapor pressure). Ultimately this is a low-temperature apparatus,
rendering vapor pressure a non-issue, but it also has to be
contaminant-free at room temp.

--Daniel

 

[Daniel Haude]

On Mon, 21 Mar 2005 16:32:27 +0000,

Yes, your experience seems to indicate that. But it may not be just
Cu/Pb. I doubt that the Cu is plated directly on to the piezo material,
and if there is, for example, a Ni interlayer there

The mfg (Staveley Sensors) says no. They usually go Piezo-Cu-Ni-Au (if you
want gold). Nickel solders by far the best, but it's magnetic.

Try using lead-free solder made for **electronics**, not the Sn/Cu stuff
used for plumbing.

I tried both (two kinds of electronics stuff and one of the other)
with the same results.

--Daniel

 

[Daniel Haude]

On Mon, 21 Mar 2005 12:01:28 -0500,

Evidently your metalization layer is quite soluble (given the
temperature and time) in the solder you are using.

Yes, it goes away almost immediately even when I set the iron to a
temperature where the solder barely melts.

--Daniel

 

[Daniel Haude]

On Mon, 21 Mar 2005 21:36:07 GMT,

Secondly: plumbers solder is not lead free, and usually uses ACID
(!!); there are numerous strong recommendations against use of plumbers
solder. And it is *not* considered fit for electronics use.

Actually what I used isn't really plumber's solder. I just called it that
because our workshop always uses it when they solder copper pipes, but it
is lead-free solder.

There are numerous *electronic* lead-free solders:
* Sn 95.5, Ag 3.8, Cu 0.7 - MP 217C / 423 F; adopted by NEMI adn many
high volume consumer OEMs

That's what I have here and what I wanted to use. After it showed those
weird effects I went back to my "old" Pb-free solder only to find that it
behaved the same.

--Daniel

 

[Daniel Haude]

On Mon, 21 Mar 2005 16:21:05 GMT,

Are you using a different iron?.
Lead free solders, except special varieties designed to handle lead
contaimination, hate having any lead present. if you are using an iron
that still has a tinned coating on the tip from using a lead based solder,
it could give the behaviour you are seeing...

That isn't it. The solder wets fine when applied to a thicker Cu surface.

--D.

 

[Robert Baer]

On Mon, 21 Mar 2005 21:36:07 GMT,



Actually what I used isn't really plumber's solder. I just called it that
because our workshop always uses it when they solder copper pipes, but it
is lead-free solder.




That's what I have here and what I wanted to use. After it showed those
weird effects I went back to my "old" Pb-free solder only to find that it
behaved the same.

--Daniel

That would indicate that the amount of copper in that is insufficent
to make it eutectic; that more copper is needed.
Contact Kester for those technical details.
One would think that they would make eutectic (or almost eutectic)
alloys.
Naturally, they would make a special alloy - but one has to be rich
for that.
Consider as a last resort of plating more copper on top of the copper
for a result of at least a mil.

 

[John Woodgate]

I read in sci.electronics.design that Daniel Haude

The mfg (Staveley Sensors) says no. They usually go Piezo-Cu-Ni-Au (if
you want gold). Nickel solders by far the best, but it's magnetic.

Not very (and if it's alloyed it may even not be ferromagnetic). You
would likely get more magnetic effects from the currents in the
interconnections.

 

[Daniel Haude]

On Tue, 22 Mar 2005 12:04:11 +0000,

Not very (and if it's alloyed it may even not be ferromagnetic).

I know it's definetely "not very", but what little there might be could be
too much. This is an STM that hangs inside a 14T magnet like a pendulum.
We found that the current model gets deflected by 1mm to the side already
at 4T. My hunch is that this is due to the nickel interlayer that was
carelessly applied when the whole thing was gold-plated. Now I'm building
a replacement and am trying to ban all ferromagnetic materials whatsoever.

That said -- I tried to make a nickel-plated 1/2" piezo scanner tube roll
on a flat surface by holding a strong permanent magnet (from a harddisk)
next to it. Nothing. That was of course at room temperature; who knows
what happens at .3K. After a few years of working with materials under
such conditions you develop a superstition.

--Daniel

 

[John Woodgate]

I read in sci.electronics.design that Daniel Haude

This is an STM that hangs inside a 14T magnet like a pendulum.

Oh, that's not playing fair! You aren't allowed to introduce a 14 T
magnet halfway through the speculations! (;-) Even so, your
current-carrying interconnections are prey to electromechanical
disruption. And BE VERY careful about using tin (Sn) at even modestly
low temperatures. Look here, and elsewhere with the search string
tin*allotropes:

http://www.physics.uoguelph.ca/summer/scor/articles/scor40.htm

ISTR that a few years ago, doubt was cast on whether 'grey tin' is
really an allotrope, rather than an intermetallic compound, but it seems
to have been redeemed.

 

[Ken Smith]

I read in sci.electronics.design that Daniel Haude


Not very (and if it's alloyed it may even not be ferromagnetic). You
would likely get more magnetic effects from the currents in the
interconnections.

This isn't likely in a piezo device since the DC currents are very very
small. There is nothing in the universe more magnetic per pound than a Ni
plating.