Lead-Free Solder: Weird Behavior

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?

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.

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

I read in sci.electronics.design that Daniel Haude wrote (in ) about 'Lead-Free Solder: Weird Behavior', on Mon, 21 Mar 2005:

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.

I read in sci.electronics.design that John Popelish wrote (in ) about 'Lead-Free Solder: Weird Behavior', on Mon, 21 Mar 2005:

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....

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.

Yes; see my earlier posting in this thread.

The UHV guys tend to hate epoxy more than lead. The epoxy outgasses at room temp and deposits organic crud everywhere, and some of that leaks out later. There are all sorts of exotic lead-free solders. Some people solder with pure indium which (I think) has low vapor pressure.

Try Kester or Multicore or Aim. They may have a lead-free solder with some copper content, which might help the leaching.

UHV is a huge nuisance. The people who do this tend to be unnaturally patient. "Well, we may have a leak or we may have a fingerprint somewhere. Let's pump it down for a week or so and see what happens."

Or use a spring.

John

On Mon, 21 Mar 2005 08:34:12 -0800, John Larkin wrote in Msg.

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

On Mon, 21 Mar 2005 16:32:27 +0000, John Woodgate wrote in Msg.

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.

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

--Daniel

On Mon, 21 Mar 2005 12:01:28 -0500, John Popelish wrote in Msg.

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

--Daniel

On Mon, 21 Mar 2005 21:36:07 GMT, Robert Baer wrote in Msg.

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

On Mon, 21 Mar 2005 16:21:05 GMT, Roger Hamlett wrote in Msg.

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

--D.

Yeah, but that big tank of helium is fun at the company party!

Cheers! Rich

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.

Second only to nitrous.

John

I read in sci.electronics.design that Daniel Haude wrote (in ) about 'Lead-Free Solder: Weird Behavior', on Tue, 22 Mar 2005:

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.

On Tue, 22 Mar 2005 12:04:11 +0000, John Woodgate wrote in Msg.

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