How does solder stick ?

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Wikipedia says:

In this soldering process, heat is applied to the parts to be joined, causing the solder to melt and to bond to the workpieces in a surface alloying process called wetting. In stranded wire, the solder is drawn up into the wire between the strands by capillary action in a process called 'wicking'. Capillary action also takes place when the workpieces are very close together or touching. The joint's tensile strength is dependent on the filler metal used; in electrical soldering little tensile strength comes from the added solder which is why it is advised that wires be twisted or folded together before soldering to provide some mechanical strength for a joint. A good solder joint produces an electrically-conductive, water- and gas-tight join.

Really difficult!

Consider an even easier example. When I drop a hammer it falls to the floor - why?

Simple answer, it falls because gravity attracts it. But what is gravity? Enter Newton, the well-known genius, who was able to quantify and define the mathematical rules behind gravity. They allow us to explain why the earth orbits the sun and why the moon doesn't fall on our heads. Using his formula mankind can safely land objects on Mars. Jolly good except none of it explains what gravity is, or why it occurs.

More complicated development: Einstein had another go at the maths because of tiny inconsistencies between Newtons work and real world observations. Einstein models gravity more usefully by inventing the concept of 'spacetime'. Gravity is explained as a surface curved due to the presence of a mass. Also jolly good except we don't know what space, time, or mass are either. The maths allows humanity to predict the real world and develop advanced technologies that work, but we still don't know what causes any of it.

Yet more complicated answer: there is an equivalence between mass and energy such that everything might be an interaction between waves and energy levels. This is very difficult to imagine because it is totally outside our experience. However, you might imagine nature preferring energy levels that are more stable than the alternatives. We cannot visualise mass-energy in terms of human scale or the 4 dimensions we experience in normal life. String theory provides better predictions by assuming ten, or eleven dimensions, but there is still something missing.

In the search for an answer to why a hammer falls, we still don't know what causes gravitational force and have made things even worse by adding energy and dimensions to the mix. What these 'are' is unknown too. Somehow energy, mass, time, space, dimensions and forces are related. It's quite likely that the forces involved in soldering - chemical bonds - come from the same fundamental root as gravitation and magnetism. Soldering is a process whereby the energy needed to hold atoms together is less than the energy needed to separate them. The strength of the join can be predicted, but no-one knows exactly why it works.

Fortunately for practical work its not necessary to understand lots of theory, unless you're attempting something new. Theory matters if you're engineering a new glue, but once it's made and sold in a tin, all the user needs to do is follow the instructions.

Dave

Do we really not know how soldering works? If you said no one knows how the female mind works I would accept that.

Mike

You obviously like living dangerously Mike!!!

Brian

Short answer is that the solder "sort of" dissolves into the surface of the metal being welded and forms a very thin layer of alloy or and intermediate compound or both.

Medium answer is that the surface of a material is held together by what is known as surface energy. Basically the atoms on the surface of the material prefer to hold hands with each other rather than wandering off into foreign territory outside. You need to put a fair amount of energy in to persuade them to break the bonds and wander off elsewhere. Obvious way is heating. Which can easily go too far and melts the whole lump unless the heat is very concentrated, as in welding, so the rest of the lump can absorb the heat without getting too hot.

When welding metal the surface is actually melted and new molten metal or the same or sufficiently similar composition laid on so the old surface is now inside the new metal and the atoms happily holding hands with their own sort of folk.

With soldering, hard soldering, silver soldering and brazing the solder material acts as a catalyst to break the surface bonds at a much lower temperature so a thin layer of some intermediate compound forms holding things together. Basically only happens where there is clean surface to surface contact so the joining layer is very thin. Some processes go a bit deeper, usually the intermediate compound composition varies with depth in such cases or may be successive layers of what should be strictly defined as different compounds. Because the metal atoms would rather hold hands wit each other than with the foreign intermediate compound the bond is weaker than welding. Generally high temperature processes are stronger because the intermediate compounds are friendlier to the metal so the atoms hold tighter..

This intermediate compound business is why tinning before soldering frequently helps. The thin tinning layer forms the intermediate compounds with the underlying material leaving a layer of solder on top. When you bring the two solder layers together and heat the solar fuses happily as its the same material but the underlying intermediate material bonds remain.

Long answer. Just don't ask! OK! I doubt if anyone really understands the general theory of exactly whats going on. Pretty much cracked at the practical level tho'.

Clive

Edited By Clive Foster on 07/12/2018 13:56:33

Edited By Clive Foster on 07/12/2018 13:57:37

Edited By Clive Foster on 07/12/2018 13:58:10

To all intents and purposes, your hammer falls to the floor because clocks go slightly slower at floor level than hand level.

This was covered in Metalwork classes when I was at school and isn't difficult to research and read up.
I always worry about anyone who does interesting stuff in which they've proven not interested enough to do even basic research and reading.

Gravity:

I forget where I read the article but essentially it explained the need for dark matter/ dark energy as a pseudo fluid with repulsive properties to explain the discrepancies of space mass and body attractions.

One can then illogically extrapolate that the failure to find a subatomic particle to call the graviton (one of the hopes for the higgs boson/field) is that there is no such thing - there is no gravity any more than there is a centrifugal force (it's centripedal). Where particles aggregate they occupy the space of dark fluid which therefore pushes them further together.. the greater the aggregated mass the greater the exclusion of dark fluid and the greater the force. Obviously less dense bodies have a small measure of dark fluid 'mixed' in.

This is the same form of idea as switching on a light switch and the bulb sucks the dark into itself. That is unarguable on the fact that the closer to the dark-suction effect the less dark there is even though it tries to flow in from afar. Indeed if you place an object between the bulb and the dark then the dark accumulates behind that object as shadow.

Yes, I like that one. I had a pal once who used to say when I came in from outdoors on a chilly night that I was radiating cold...

I suppose this will lead to a "why do slip gauges stick together?" thread.

Indeed. It's easy to forget that a steel girder is an active gas constrained by a lack of energy into a slow moving liquid and without enough gap between two such liquids they tend to mix together.... time for me to get my coat..

... (it’s centripedal)...

I think it might be centripetal. So more to do with flowers than bicycles?

Since Mike likes to live dangerously it begs the question- Are there any Members here of the female persuasion?

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Can I just thank Silly Old Duffer for his wonderful, entertaining, and easy to follow descriptions of things. S.O.D, please tell me you're a teacher?

You are much too kind - I often get things wrong!

Sorry to say I've never been a teacher. I've done a lot of communicating as part of my job; I'm told by those forced to listen that my only asset is a strange sense of humour!

Dave

Just for completeness....

Straight Man Sam : "How does solder stick?"

Big Torch Bob: "Pretty well , generally , if you use flux and have enough heat"

Years ago a friend, who was senior lecturer in flight dynamics at Cranfield, once pointed me in this direction:

**LINK**

A theory no doubt that pgk pgk is familiar with.

Rik

P.S I tend not to fly these days!

pgk pgk says...

One can then illogically extrapolate that the failure to find a subatomic particle to call the graviton (one of the hopes for the higgs boson/field) is that there is no such thing - there is no gravity any more than there is a centrifugal force (it's centripedal).

I'm only a simple engineer and will stand corrected, but it seems to me that in order for an object to stay in the same place on a rotating plane there must be two forces at work, centripetal and a restraining force , as Mr Newton said that for every force there is an equal and opposite force... What do we call this restraining force..?

Bob...