How does solder stick ?

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Bob Mc on 08/12/2018 19:20:39:

… was challenged originally by the late Eric Laithwaite who's theories were later discounted by the academics and his televised lecture was 'expunged'.. I think the word was.

I am not going to elaborate on this further as it starts to get quite involved and is not what the topic intended.

.

With apologies for compounding the felony of digression …

Bob : I remembered finding this page, a while ago: **LINK**

http://www.gyroscopes.org/1974lecture.asp

… enjoy !!

MichaelG.

[Neil WyattModerator @neilwyatt]

Posted by Bob Mc on 08/12/2018 19:58:00:

So I stand by my original post, that there must be two forces equal and opposite on an object in orbit, whether it be a gravitational force or the force of mechanical restraint…this force must be towards the centre of rotation, whereas a 'Centrifugal' force would be away from the centre and is the reaction to the centripetal force.

….Now my brain hurts…!

No, a body with no force on it exists in a state of rest or uniform motion. Orbit isn't uniform motion, after half an orbit the object is heading in the opposite direction. Clearly gravity is changing its motion, if something was opposing it the object would be stationary.

Laithwaite's point is :

Whirl a weight around your head on a string, a centripetal force is pulling the object keeping it rotating. Cut the string and it doesn't fly directly away from you (pushed by a centrifugal force) it just carries on tangentially as the force making it rotate is no longer there.

The opposing force in the string is what makes you wobble as you spin the weight, just as the moon doesn't actually orbit the centre of the earth – the moon and earth both orbit their 'barycentre' which is just below teh surface of the earth, facing the moon.

Neil

[pgk pgkParticipant @pgkpgk17461]

..and to digress further (since I'm a culprit anyway). I understand that centrifugal force isn't a force in it's own right but a mathematical nicety as a component of the changing angular thrust of the tangent of the orbiting object that is restrained by tether or gravity that is the centripetal force. And to obfuscate things further speed is a scalar quantity since it only has magnitude but velocity has both magnitude and direction. A rate change of velocity is acceleration thus a body at constant speed (component of it's velocity) but with a rate change.. in this case a rate of change of direction is also an acceleration…?

I did start writing a long overly involved suggestion as to how I see different things 'stick' but the simplest way I look at it is the differences between an 'adhesive' that penetrates gaps in the surface like roots and that which develops a genuine chemical bond. The first would also be true where materials 'melt' into each other forcibly as opposed to two perfectly clean and smooth surfaces of identical materials re-organising themselves into a contiguous whole. I view that as a difference between steel (say) being a cold liquid and a crystal being an ordered lattice.

[Andrew EvansParticipant @andrewevans67134]

Maybe Richard Feyneman can help here https://www.youtube.com/watch?v=MO0r930Sn_8

[Former MemberParticipant @formermember19781]

[This posting has been removed]

[Tim StevensParticipant @timstevens64731]

Sorry, pgk pgk, but steel is crystalline. Heat treatment changes the layout of the atoms in the crystal, but it is crystal and not super-cooled liquid. For an example of this latter, try glass as in window. (And not, although it looks much the same, rock crystal. The clue is in the name)

Cheers, Tim

[Andrew EvansParticipant @andrewevans67134]

Was it?

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Tim Stevens on 08/12/2018 21:31:15:

… not super-cooled liquid. For an example of this latter, try glass as in window. (And not, although it looks much the same, rock crystal. The clue is in the name)

.

Unlike 'lead crystal' … where it isn't

MichaelG.

[andy mulhollandParticipant @andymulholland30577]

could I thank all you gentlemen for keeping me well entertained reading this thread, and encouraging my brain to maybe start working again…. me head is hurting. thanks… Andy

[pgk pgkParticipant @pgkpgk17461]

Posted by Tim Stevens on 08/12/2018 21:31:15:

Sorry, pgk pgk, but steel is crystalline. Heat treatment changes the layout of the atoms in the crystal, but it is crystal and not super-cooled liquid. For an example of this latter, try glass as in window. (And not, although it looks much the same, rock crystal. The clue is in the name)

Cheers, Tim

Thanks for the correction. But is it one large crystal or an aggregation of tiny crystals floating together compared to say a diamond ?

pgk

[duncan webster 1Participant @duncanwebster1]

It's lots of small crystals unless you're very clever like Rolls Royce and manage to make single huge crystals from which to make gas turbine blades.

A good book to read is 'The New Science of Strong Materials' which explains it all in understandable language.

[Robin GrahamParticipant @robingraham42208]

I think the way solder works is probably fairly well understood, at least within the framework of physics / chemistry as we know it – a cursory search revealed this interesting photomicrograph*:

I'm sure there is much more info available on t'internet if one were to search more diligently.

Posted by pgk pgk on 08/12/2018 20:36:51:

A rate change of velocity is acceleration thus a body at constant speed (component of it's velocity) but with a rate change.. in this case a rate of change of direction is also an acceleration…?

Yes exactly, that's what Neil was saying I think. Things either stay at rest or carry on in a straight line unless an external force acts according to Newton's first law – so in the case of two bodies rotating about their centre of mass (barycentre) the force is always towards the centre, bending their natural trajectories.

It's a bit more complicated when straight lines become space-time geodesics of course!

Robin

*Evaluation of the Effects of Au Content on Intermetallic Compound Layer Growth

in Pb-Sn and Sn-Ag-Cu Solder Joints

D.F. Susan, P.T. Vianco, J.A. Rejent, J.J. Martin, and P.F. Hlava

Sandia National Laboratories, Albuquerque, NM USA Proceedings of the 3 International Brazing and Soldering Conference, April 24–26, 2006, Crowne Plaza Riverwalk Hotel, San Antonio, Texas, USA

[not done it yetParticipant @notdoneityet]

Of course, all this assumption of plain crystalline lattices perhaps does not consider solid solutions or interstitial atom/molecules/particles which, while not actively chemically combined with any crystal stucture may assist in changing the relative structural strength (or other properties) by simply filling any spaces within the structures. So rather more complicated, in many cases, than simply considering a material ad crystalline.

Flawless crystals for turbine blades might be compared with the diamond structure, which will fracture at the right angles for total internal reflection – as long as the job is done properly… nothing to do with solder, but that was probably sufficiently explained in the first few posts, for the OP’s question to be answered.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Robin Graham on 08/12/2018 23:54:28:

I think the way solder works is probably fairly well understood, at least within the framework of physics / chemistry as we know it – a cursory search revealed this interesting photomicrograph*:

…

Disagree slightly in that although I agree the Chemistry is well understood, the Physics is surely still mysterious. At least if you dig deep enough.

The photo is interesting for another reason. It appears to suggest that the bond is made only by alloys of Copper and Tin created when the solder is melted. (ie Bronzes.) In the picture Lead doesn't appear to play any part in the sticky part of soldering. Presumably Lead is mainly a component of solder to reduce the melting point of tin and then to allow it to flow into contact with the copper. Lead doesn't add strength. The implication is that wide gaps filled with solder will make much weaker joints than those where the soldered items are close together.   (You all knew that anyway!)

As lead is a poor conductor of electricity I've often worried about soldered joints in electronics. Solder seems a poor way of making electrical connections especially at RF – why aren't joints high-resistance due to the poor electrical qualities of the solder? Lead is 20 times less conductive than Copper and Tin not much better – about 10 times inferior. Having seen Robin's photo, I now think the electrical bond is a thin layer of Bronze formed between copper conductors. Bronze is a better conductor than solder. The lead blob usefully surrounds the actual electrical joint and protects it from oxidation. However, as Bronze is only twice as conductive as Tin, that explains why solder guidelines emphasise the need for electrical connections to be mechanically sound, ie in good contact, before soldering.

Dave

 

 

Edited By SillyOldDuffer on 09/12/2018 12:07:35

[Keith HaleParticipant @keithhale68713]

What a marvelous response from Robin.Brilliant!A terrific picture that shows what happens and illustrates just why thin solder and brazed joints are stronger. Thanks for your contribution to the campaign.
Regards
Keith

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