Does solder seep into copper plate ?

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Bit of a Steven Hawkins question and black holes. Is Tin/Lead absorbed at molecular level when soldering(sodering) Copper. The old Silver Soldering nugget, If you did this, don't do that. How lucky do you feel with regards to a pressure vessel????

You're gonna need a rocket scientist with access to an electron beam microscope for this one.

Regards Ian.

Wouldn't be surprised at one poster dropping the definitive answer.

Edited By Circlip on 16/01/2020 13:14:29

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It is generally considered that in lead/tin solder ( and I guess to some extent lead free) that an alloy layer forms tin-copper

If you etch with acid the tin may be left with copper being removed first ( my recollection of relative reactivity is hazy)

I know in brass(copper zinc) The zinc can go first leaving spongy copper behind...but don't know it is in tin copper being ( bronze seems more durable)

Yes soldering does result in alloying between the solder and the surfaces of items being joined.

I think Jason's right, but at the microscopic level even highly polished surfaces are full of difficult to clean valleys and caves. Depends on how clean the surface needs to be, but I recall the extreme measures taken making electronic valves. Whilst being carefully exhausted by the best possible vacuum pumps the fine metalwork was heated strongly to de-gas it. Then the valves were sealed with an active 'getter' inside to soak up any stray atoms still floating about. Failing to remove a few loose atoms markedly reduced the valve's electronic performance and its operating life.

The problem with pickle is that it will dissolve Copper rather than Lead or Tin. Thus to get rid of all the old Solder it would be necessary to strip the copper underneath, leaving the solder particles to fall off. No idea how deep the solder layer might be, I'd guess microns rather than thou. As Pickle doesn't react strongly with Copper, I'd suggest an abrasive instead.

Dave

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Here's some background reading, courtesy of copper.org [the obvious first point of reference] :

**LINK**

https://www.copper.org/applications/marine/cuni/pdf/Broschuere_Loeten_ENG.pdf

MichaelG.

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No problem, Bill ... You're welcome

[it's usually just a matter of knowing/remembering where to look]

MichaelG.

Whilst copper oxide will react with sulfuric acid as a redox reaction the copper metal itself, for all intent and purpose does not react and will be unaffected. This can be demonstrated by leaving a clean piece of copper in a bath of conc sulfuric acid for six months (or by losing a boiler end plate!) and then upon finding it checking its condition and thickness...unchanged so far as is possible for me to detect. Not suprising since copper is one of the least reactive metals we have. So whilst the pickle will remove the oxide layer it wont remove the solder which may be engrained in its surface. Funnily enough we bought our daughter a microscope for christmas and last weekend put a piece of new 'flat', smooth copper plate on for her to see what the surface looks like. Even at relatively low magnification it is very rough.

Further to my last.

In the electronics industry.

We from time to time need to verify the lead free status of components .

Lead detection "pens" exist for this purpose.

So for the purpose of detecting leaded solder than maybe these might be illuminating.

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Michael has a magic touch finding interesting internet references! Couple of quotes from his latest, my bold:

'A soldered or brazed joint comprises the heat-affected parent materials, the diffusion/transition phase and the solder/braze metal.'

And:

Formation of the solder/braze metal through (physical and chemical) inter-action between the molten filler and the parent material.

And:

After soldering or brazing, alloying elements from the filler metal can be found in the parent material and alloying elements from the parent metal are detectable in the filler metal. This change in the chemical composition is referred to as diffusion. Although the parent material does not melt, a diffusion zone is established in the wetted area. An alloying element in the parent material and at least one of the alloying elements in the filler alloy combine to form a solid solution, a eutectic system or an intermetallic compound. Phase diagrams can be consulted prior to soldering/brazing to determine whether any diffusion will occur between the metal pairs. Diffusion is both time- and temperature-dependent. The time spent at the soldering/brazing temperature ( the ‘holding time' ) should be as short as possible to prevent extensive alloying within the parent metal or the formation of brittle phases in the transition zones. To achieve optimum strength in the soldered/brazed joint, the filler metal needs to remain in its liquid phase for several seconds so as to create a sufficiently deep diffusion zone.

Not found anything stating how thick the diffusion zone might be, but the relative scale of Figure 4 relative to Fig 13 suggests it could be significantly more than my micron suggestion, perhaps 0.1 to 0.4mm.

Quite interesting info on the timing of joint making. It probably explains why the joints made by clumsy erratic me with a weak torch aren't half as good as the sort of work Fizzy does!

Anyway, Bill has his answer - it isn't safe to assume all the solder is removed!

Dave

Edit: Removed pesky emoticons...

Edited By SillyOldDuffer on 16/01/2020 15:28:18

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There's no 'magic touch' involved, Dave

As I wrote earlier "[it's usually just a matter of knowing/remembering where to look]"

I remembered copper.org from previous visits, and just put 'lead solder' into their search box

A few seconds skimming that document confirmed that it contained the words and pictures I was looking-for.

MichaelG.

Why not create the conditions you describe on a similar piece of scrap copper plate.

Then silver solder your test piece to it.

You will soon see what happens if there is too much soft solder left around !

In principle I don't suppose the distance could be comparable to the penetration during case hardening or nitriding, as the temperature is lower, but this might be countered by the mutual solubility.

Neil

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