Question About Soldering Technique

[IanB]

Watching this video a couple times, I find myself more confused. The solder makes scant contact with the wire. It looks like the solder is coming more from the bottom, and it looks like he is using the iron's tip to "brush" the solder over the wire. What do other people think?

Yes, that is exactly what is happening. He creates a solder bead on the iron and then he allows the solder to get sucked onto the wire using surface tension and capillary action. You may think he is breaking a "rule", but this just shows that all rules are made to be broken. The reason it works in this case is that the wire was first covered with liquid flux. The rule about not applying solder directly to the iron applies when no extra flux is being used and the only flux is inside the solder. In the latter case you want the flux to melt onto the work and not onto the iron.

If you watch videos on drag soldering of SMT components you will see exactly the same technique being applied, where a solder bead is dragged along the pins. Once again this only works when lots of additional flux has first been applied to the work.

[IanB]

Ultimately molten solder wants to move towards the heat source

This is not really the case. Solder will flow over any surface it can wet, just like other liquids. The appearance that solder flows towards heat is a side effect of heat activating the flux which allows the solder to wet the fluxed surfaces. But otherwise the solder will flow anywhere it can, for example it will flow up under the insulation of a wire even when that is not wanted.

[rx8pilot]

Ultimately molten solder wants to move towards the heat source

This is not really the case. Solder will flow over any surface it can wet, just like other liquids. The appearance that solder flows towards heat is a side effect of heat activating the flux which allows the solder to wet the fluxed surfaces. But otherwise the solder will flow anywhere it can, for example it will flow up under the insulation of a wire even when that is not wanted.

Sort of....as the solder flows away from the heat the temperature rapidly falls and the solder cools and stop flowing. It flows best close the heat source because it is fully molten in that area. By the time the solder melts, the chemical action of the flux has already been used up.

Personally, I have my own technique similar to what GreyWoolfe described. Whether it's wire-wire or wire-to-contact I use sticky flux on both sides of the joint, then put a blob of solder on the tip of my iron, touch the blob to the joint that already has flux on it. The flux activates and the solder flows very quickly and without unnecessary heating of the joint. The instant the blob of solder makes contact with the flux, the heat transfer is very good and the brief moment where the flux has done it's work - the solder is there ready to go. The biggest reason I do it this way is that I only have two hands - one for the iron and the other for the wire. I don't have to hold the solder wire at all.

This one, although you can get smaller packages.
https://www.digikey.com/product-search/en/soldering-desoldering-rework-products/flux-flux-remover/1311241?k=flux&k=&pkeyword=flux&pv16=15070&FV=fff40014%2Cfff80209%2Cfffc013b&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

[CraigHB]

I don't think touching or not touching the tip to the splice is going to make any appreciable difference.  The main thing is to get the joint hot enough for the solder to wet and flow.  For any solder job contact with molten solder from the tip is required for heat to flow into the joint.  The distance of the tip from the joint is probably not a critical thing as long as melted solder is in contact.  Now if the tip is dirty or there is a lack of wet solder the joint will not absorb enough heat to solder properly.  That's kind of just basic soldering technique.

Solder splicing stranded wires is something that seems to be a need more often than you would think.  It's always a pain and twisting them together results in a bulge of solder and wire at the splice.  What I've been doing lately is kind of knitting my splices.  What I do is push the two bare ends together so the strands interlace then I bind them with a wrap using a thin strand from a high strand count wire.  After binding and fluxing I get a joint that's not much thicker than the single wire itself.  After a shrink wrap it looks really clean.  It does take some time to bind the wires, but it's worth it to avoid the wires invariably loosening up and turning into a big blob of solder.

[hizzy]

I don't think touching or not touching the tip to the splice is going to make any appreciable difference.  The main thing is to get the joint hot enough for the solder to wet and flow.  For any solder job contact with molten solder from the tip is required for heat to flow into the joint.  The distance of the tip from the joint is probably not a critical thing as long as melted solder is in contact.  Now if the tip is dirty or there is a lack of wet solder the joint will not absorb enough heat to solder properly.  That's kind of just basic soldering technique.

Solder splicing stranded wires is something that seems to be a need more often than you would think.  It's always a pain and twisting them together results in a bulge of solder and wire at the splice.  What I've been doing lately is kind of knitting my splices.  What I do is push the two bare ends together so the strands interlace then I bind them with a wrap using a thin strand from a high strand count wire.  After binding and fluxing I get a joint that's not much thicker than the single wire itself.  After a shrink wrap it looks really clean.  It does take some time to bind the wires, but it's worth it to avoid the wires invariably loosening up and turning into a big blob of solder.

Would you have a photo of the knitted splice? Thanks!

[P90]

I've got an old tin of Radio Shack flux.  It's transparent and amber in color, a smooth gel.  Best I've ever used, better than anything dissolved in IPA (it doesn't spatter and run away from the heat!), and better than the most common types of name brand fluxes!

Tim

Not to mention  IPA ruins your iron tips...

[CraigHB]

Would you have a photo of the knitted splice? Thanks!

Sorry I don't have a photo, but if I get a chance I can do an example splice like that and post a photo.

[hizzy]

Hi Everyone!

Thank you for all of your help. It's interesting to see that the rules of soldering are not as rigid as I thought. There are many different techniques that can deliver great results.

I was curious about how most of you go about tinning your iron before soldering. There seems to be a slight difference in how people do this. I have noticed that some people clean the tip on their sponge/brass sponge, add solder to the tip, and then go straight to soldering. Others, clean the tip, add solder, and then clean the tip a second time, wiping excess solder off of the tip. Is one method preferable over the other or is this just another example of how soldering is flexible in its methods?

Thanks again!

[Ian.M]

It depends - its a lot easier to get the tip retinned evenly with excess solder then wiping it off, and for some work you need a clean tip with minimal extra solder but its far faster to simply wet the face of the bit with a little solder and go straight to the joint.  As long as you do a proper job of retinning the bit evenly before leaving the iron in its rest for more than a few minutes so you don't end up with oxidised unwettable spots, you can get away with the shorter method for most work.

[nanofrog]

NASA's Student Workbook for Hand Soldering might be of interest, as is their Pictorial Inspection site.

[hizzy]

The links above are very interesting! The NASA example confuses me, though because tinning the tip is step number 7. They don't seem to tin the tip before to soldering.

[IanB]

The links above are very interesting! The NASA example confuses me, though because tinning the tip is step number 7. They don't seem to tin the tip before to soldering.

You clean the tip just before soldering, so that it is bright and shiny. Cleaning removes any old solder, oxides and dirt so that these do not contaminate the joint. As long as the tip was already covered in solder before cleaning it will remain tinned (tinned just means covered with a film of solder).

[hizzy]

I was under the impression that I should clean and tin, prior to soldering each joint/wire/etc... Prior to use, each time I solder I clean the tip, add solder, and then wipe the tip again. I thought that was "standard", but I'm starting to think my method is flawed.

[suicidaleggroll]

I was under the impression that I should clean and tin, prior to soldering each joint/wire/etc... Prior to use, each time I solder I clean the tip, add solder, and then wipe the tip again. I thought that was "standard", but I'm starting to think my method is flawed.

That's pretty excessive.  You can do many joints in a row before needing to clean the tip again.  Just keep an eye on it, when it starts to accumulate a significant amount of cooked flux to the point where it becomes difficult to get good contact with the joint (or when it accumulates a blob of solder large enough that it starts causing problems), you need to clean it.  With small joints this might happen every 5-10.  With large joints it's quite a bit more.  In addition to that, clean and tin when you first start soldering, and again before putting the iron back in the holder when you're going to leave it for a while.

[GreyWoolfe]

+1.   When I am done, I take an extra step that when I turn off my stations, I add a blob of solder to completely cover the tip.  That gets removed when I turn the stations on again.

[Brumby]

If you're becoming confused about the 'rules' of soldering - it's because you are overthinking things.  You need to just understand the basics ... and then learn by doing.

Basic No 1.  Flux.
Note: In the following, I will be talking about using a flux-cored solder, with no external flux - for one very specific reason ... you will get to understand the basic process much better.  This will mean that, when you come to do your own soldering, with or without additional flux, you will know what's going on - and have a better idea of what you can and can't get away with.
Solder bonds to clean metal - not dirty, oily or oxidised surfaces.
 - If the object to be soldered is particularly dirty, mechanical cleaning may be necessary.  For critical applications - such as aerospace - mechanical cleaning may be required on any surface to be soldered, no matter how clean it may look, to ensure it is as free from contaminants as possible.
 - Even freshly cleaned metal will oxidise in a short time - and heating the metal will accelerate this
 - Flux is used to dissolve these oxides and allow the solder to bond with the metal
Now for the biggie....
 - Flux will deteriorate from the heat of soldering.  Since it is important to have it working on the surfaces to be soldered, a lot of the 'rules' circle around this very specific issue.  If you keep just this one thought in mind, then a LOT of what might be confusing to you now will become much clearer.

Putting a blob of solder on the tip of an iron and then transferring this blob to the workpiece with the intention of using this blob of solder as the jointing material is the absolutely WRONG thing to do.  If you see people who have been soldering for a while doing this ... look more closely.  You will probably find they are simply adding a blob of solder that they can bring to the workpiece to allow better heat transfer from the iron to the work (The molten solder wraps around the joint and provides more surface area for heating - even if that solder doesn't 'wet' the joint.)  Once the joint is heated, you can apply flux cored solder where the flux removes the oxides and the solder wets the joint. (Yes, you will probably see some of the blob get sucked into the joint, but that wasn't the point.)

Heating the joint and applying the solder can be done in one of 3 ways - and how good or bad each method is is directly related to the degree of degradation of the flux.
1. Heat one side of the joint and apply solder to the other, so that the solder is melted by the joint, not directly by the iron.  While this is best for flux preservation, the joint will be subjected to more heat - so you need to be aware of this and consider the risk of heat damage to what is being soldered.
2. Heat the joint and apply the solder to the joint and the iron at the same time.  This gives quick melting of the solder and the flux is very close to where it needs to be.
3. Adding solder to the iron and then applying this to the joint.  A bad practice to get into - but if you do find it necessary to do something like this (in drag soldering, for example) you are going to need external flux for a reliable result.  With this method, as you carry the blob to the workpiece, that wisp of smoke is the flux burning up - so you need to have flux already on the workpiece.


Basic No 2. Heat.
You will need a certain amount of heat to complete a joint.  This is a function of time and temperature.  Too high a temperature can cause a lot of problems .. from flux vaporising before it can do anything to frying components.  Too low a temperature is also bad if it increases the time it takes to do a joint.  You might feel it's doing less damage, but you are just using the 'slow cooker' approach.  If the iron is hot enough to melt solder, it's hot enough to do damage.  Look at a few videos of people with some experience to see how long they take to do a joint - a lot of the time it's under 2 seconds.

Basic No 3. Tip - size and shape. 
Use a tip on the soldering iron that is appropriate to the joint.  Thick tips can hold more heat closer to the joint, so you can finish the joint sooner, but they can be clumsy.  Also, use a tip with a shape that reasonably matches the surfaces being joined.  Better surface contact will carry heat into a joint more quickly.  This is why nobody here has much in the way of positive comments on round tips.

Basic No 4.   Solder.
There's a lot to discuss here - but if you're just getting into it, a 60/40 or 63/37 flux cored solder is where I would start.

Basic No 5.   Iron.
Some might complain this should be higher up in the list - but if you understand what is going on, you can do decent solder joints using a nail and a blowtorch.  It won't be easy and it won't be efficient, but it can be done.
The main thing is, to get something appropriate to the type of work you will be doing - and if you're serious about electronics work, spend the money on a decent temperature-controlled iron.

[SeanB]

The one thing that gets me is every person who handles bare solder with fingers. I always use a small tube and coil up some solder inside, using as a source of tubes those plastic packs you get vitamin tablets in, or for a lot of my use a small plastic push on handle for piping, with a bottle cap as an end, and a hole in the end to feed the solder out. keeps the solder from contamination by oil, and also keeps your hand free of wiped off lead as well.

As a bonus you can have 3 tubes with different sizes of solder in a small tray, and no mucking about with reels that unwind, fall over or that simply are unwieldy to use. To refill I use a plastic BIC pen, and chuck it in the cordless drill, start the one end with solder into the chuck, and wind away off the roll making even layers till it is the right thickness to just fit the tube, then stop, remove the pen and put it in the tube. The end placed in the chuck then is fed out the hole, and you put the cap on and are done for a few dozen meters of solder.

[mariush]

Or you could buy some nitrile gloves like Louis Rossman does and this way you can still FEEL the solder in your hands as you work with it, instead of messing about with tubes and other things.
They're around 10 cents or less, if you buy in volume.

[CraigHB]

I've been handling my solder bare handed for years.  I have no idea the risk of lead poisoning that way.  Can you even get lead poisoning through your skin?

[SeanB]

Do you wipe your face without noticing it, scratch your face or just generally touch without washing your fingers, then you will get some transfer of the oxides to your interior, and with damp fingers some soluble lead compounds ( from reaction with sulphur and amines in your skin) will be diffused through.  As lead is a cumulative poison it is best to minimise exposure, though the major source of lead in your body is from water ( Hello Flint!), the air you breath ( TE lead in fuels and in coal burnt in power plants and in burning of garbage) and in your food. Solder is a pretty low amount, but still worth minimising.

Fun thing is the 2 sources of mercury you are exposed to is fillings with amalgam, and fish, with the fish being the higher source of it as well, especially salmon, but it is there in all predatory fish, along with DDT.

[Ian.M]

There's minimal skin contact risk from solder wire unless you smoke or eat without washing your hands.  SnPb solder paste is a different matter as the combination of micro-particles and flux activators may result in traces of organo-Lead compounds and the solvents increase the risk of skin adsorption,.

[P90]

Or you could buy some nitrile gloves like Louis Rossman does and this way you can still FEEL the solder in your hands as you work with it, instead of messing about with tubes and other things.
They're around 10 cents or less, if you buy in volume.

I don't care for gloves... you lose the sence of feel... same goes for condoms...   

[T3sl4co1l]

Please... remember to practice safe soldering.  Or else you'll need to take the pill*!

(*Which I think is actually injections, not a pill, so have fun with that.  Of course, it would only come to medical treatment (chelation therapy) if you're really daft, and eat the stuff, or rub it all over your body.  Just... don't do that.  Washing hands after handling?  Stupidly effective.)

Tim

[P90]

Please... remember to practice safe soldering.  Or else you'll need to take the pill*!

(*Which I think is actually injections, not a pill, so have fun with that.  Of course, it would only come to medical treatment (chelation therapy) if you're really daft, and eat the stuff, or rub it all over your body.  Just... don't do that.  Washing hands after handling?  Stupidly effective.)

Tim

I played with lead toy soldiers and cars when I was a little kid, probably chewed on them more than I can remember, I turned out fine... I think... anyway, they make too big a deal out of lead. I'd be more concerned about mercury...

[tggzzz]

Do you wipe your face without noticing it, scratch your face or just generally touch without washing your fingers, then you will get some transfer of the oxides to your interior, and with damp fingers some soluble lead compounds ( from reaction with sulphur and amines in your skin) will be diffused through.  As lead is a cumulative poison it is best to minimise exposure, though the major source of lead in your body is from water ( Hello Flint!), the air you breath ( TE lead in fuels and in coal burnt in power plants and in burning of garbage) and in your food. Solder is a pretty low amount, but still worth minimising.

Fun thing is the 2 sources of mercury you are exposed to is fillings with amalgam, and fish, with the fish being the higher source of it as well, especially salmon, but it is there in all predatory fish, along with DDT.

Your case would be more convincing if you replaced the adjectives with numbers, even rough numbers.

You should compare the risks from lead in a solder wire, with lead in solder paste, with lead from the environment. Examples of the latter: 20 miles from my house you can't grow and eat your own vegetables due to the Pb and Cd in the soil, and some of the water pipes coming to my house are made of lead.

For the latter, I've removed adjectives and measured the results of taking and not taking simple precautions.

You should then compare the micromorts associated with lead wire, radon, smoking, and - especially in South Africa, "traumatic lead poisioning".

FFI on micromorts, see https://plus.maths.org/content/os/issue55/features/risk/index