cutting cored solder before soldering?

[coppercone2]

I swear a long time ago I saw in a video that for best soldering practices you should cut the solder before you solder if you are used cold solder so the flux 'pours' out on the tip of the iron, that is, before every time you use the solder you cut it.

Has anyone seen this before?

What kind of cutting tool would you even use on something like 0.5mm multi-core brand solder to allow for a flux release pass? I feel like even ultra flush cutters would 'crimp' it closed during the cut.

[IanB]

This is standard practice for work done to prescribed standards in aerospace or defense industries. For home soldering it is irrelevant.

The reason is to make sure there is fresh flux inside the wire at the point of solder application. This reduces the risk of a bad joint.

To cut the solder just use a simple pair of end cutters. Solder is wire is soft, no special tools required.

[Shock]

NASA hand soldering training includes cutting solder in their standard. The other one I've seen is cleaning the solder wire. You can always test if there is flux in the end of your wire, and how dirty your solder wire is. If you are following a critical reliability standard then do it, otherwise it's unnecessary unless you have dirty solder wire or experience poor wetting (see below).

I'll also argue that part of that standard makes two contacts with the solder wire. First to the iron to make a thermal bridge then to the target. So to me that blurs the lines on how effective the practice of cutting the solder wire actually is.

Standards (I'll use IPC for an example) are both process and results based. 99.9% of people don't even meet the criteria of Class 1 - (in basic terms) acceptable joints and a functional circuit. Then there is Class 2 - continual performance and extended life and Class 3 high performance, critical or harsh environment.

As long as your solder is wetting well and your joints are acceptable that is your primary focus for soldering at home. Use a quality multicore solder with a suitable flux and you will be fine.

Now that I have said that there are some parts of those high reliability soldering techniques that are good practice. Cleaning the tip so it is well tinned and shiny, cleaning the target area or component, and adding flux anywhere you need for optimal wetting, these things make a huge difference.

[exe]

I wouldn't bother with this. If in doubt, apply "external" flux. I rely on visual inspection to judge my joints and adjust the process (temperature, amount and type of flux, tip type, etc) until result is satisfactory.

[coppercone2]

ok but if you do want to bother with it, how do you cut thin multicore solder to their standards?

what tool is used? are you supposed to inspect it under a microscope to 'see' if there are flux pathes that are exposed or is it just trusted?


I am just trying to imagine what the hell is going to make a clean cut on a thin mallebale wire like that.

My swanstrom sc15e sheer cutter is cutting kester 0.02'' so I can see a dot in the middle which I think is flux, but I have a feeling it won't work for multicore brand. Maybe if the cutter is brand new. Mine is pretty well worn but it does seem to 'cleave' it so I can see a filler hole in the middle. If there are 5 cores inside of a 0.02 inch wire I have my doubts??

Are you supposed to use like a carbide sharpened sheer cutter? Ultra flush carbide cutters are just 'crimping' the center closed on their pinch point, as small as it is (for a 200$ cutter).


maybe this?
https://denovodental.com/products/instruments/wire-shear/

[Ian.M]

It doesn't matter how you cut it or even if you snap it, as the flux cores will still be present right up to the end, but if the end was melted by an iron, there is a remote possibility that most of the flux has boiled out of the solder next to it and a stronger possibility that the flux has been deactivated by thermal cycling, which would be undesirable if only a very short length was used for each joint as the first would get very little if any flux.

Don't worry about it if you are doing hobby work or using extra flux.


OTOH cleaning the solder can be important, especially if its old or poorly stored.  In an industrial or MILSPEC environment, you'd discard or recycle date expired solder, but as solder with non-corrosivev flux core doesn't go bad but instead just develops a thicker and thicker oxide layer on the exterior that eventually compromises solderability, it can be worth cleaning it if you can see any oxidisation or if you are experiencing solderability problems.  Heavily oxidised solder wire is best cleaned when you refill your bench dispenser or minispool rather than  at point of use.   Personally, I find pulling it through a folded green panscourer before wiping it removes more oxide more effectively than just wiping it with IPA.

[coppercone2]

I thought it was designed to flow out of the opening right before the solder melted and drip onto the joint so that you needed a open path.

Does it squirt out through the 'crimped' end after a cut with anything other then good shears?

Like if you look carefully at sheer cut solder, you actually see the flux. I can imagine it melting and pouring out. If you cut it with cutters that rely on anvils (anything other then sheer) you get this /\ shape in the middle where it necked down and it looks like it closed off the flow.

[IanB]

You're overthinking this. The solder melts the instant it touches the hot iron, at which point all concepts of "tube" and "open path" disappear. You have a molten pool of solder with no containment ability at all. This is why cutting the end for home soldering doesn't even matter. The solder melts and the flux is released.

[coppercone2]

here is the picture results. I think you are right in thinking it does not really matter (keep in mind the sheer cutters are a bit worn but you can see that they 'work' when you cut heavier wire.

this is with 0.5mm solder Kester single core

It seems the difference between ultra flush carbide cut, sheer cut and regular high end flush cutter (steel) is similar.

They all look like cysts. 

It's not instantaneous, if it was there would be time travel. Its just fast. I would need to take high speed video zoomed in to see what happens exactly.

The cheap flush cutter (well compared to the medical electronics grade one) seems to squash it into a oval just a bit.

[Shock]

You can test the flux in solder by putting an exact amount on some bare copper clad pcb. Weigh it perhaps if you have some accurate scales. Then hit it with hot air at a low speed setting. If you do it in a controlled manner you can probably work out exactly how much of a difference it makes.

I use mostly SnPb rosin multi core so it's probably one of the least likely to dry out or deactivate. But like I said in my other post, it's both the process and results that are the basis for quality. If you are getting horrible joints even after cutting the solder you got other problems.

[David Hess]

Where this matters, I wet the tip of the iron with the end of the solder and then wipe the tip immediately before I start.

[coppercone2]

I think what I saw in the video is that they had two spools of solder, one for wetting and one for soldering so they can cut it but I saw this on youtube back in like 2014 and I don't remember very well. It seemed obnoxious.

Or maybe they were against wetting all together.

[Electro Detective]

Have a small container of good (NON PLUMBERS!  ) flux handy, and dip the end of the solder in about 2mm, or whatever depth works,
then hit on the heated joint, or for some coolish lazy iron 'heat encouragement'

That's a lot quicker than cutting and wasting solder/sodder, and I reckon does a better job of it = EMMV

Besides, unless you perform a really clean mini samurai cut on the solder ends with an expensive sharp nipper,
all you are doing is squashing in the flux core at the cut end anyway,
or cutting and sealing if using a blunt cutter = waste of time and effort.

and you'll have to clean any cutter used after a number of slices, as the flux will turn into a crusty sticky mess, affecting the precision of further cuts =   

fwiw I have used this routine in tight spots I did not want to revisit or suspect later 

[coppercone2]

well you saw the picture, those cutters are all well used and it looks OK imo.

[David Hess]

Have a small container of good (NON PLUMBERS!  ) flux handy, and dip the end of the solder in about 2mm, or whatever depth works,
then hit on the heated joint, or for some coolish lazy iron 'heat encouragement'

I do that for difficult joints.  Kester even used to sell paste flux.

[coppercone2]

dip the iron into the flux after you tin it maybe? or is that too much?

[coppercone2]

I am almost thinking like there should be a solder dispenser that spits the solder out through a 'oiler' wick covered in warmed flux.

[Berni]

The iron doesn't need any flux on its tip!

The only purpose of the flux is to clean your solder joint so that solder can stick to it properly and make a good connection. Its simply a chemical that once heated to a certain temperature becomes really reactive and begins forcefully ripping oxygen atoms out of anything it comes in contact with. This removes oxide layers off metal surfaces.

Even if you don't cut it once the solder wire melts the angry oxygen stealing chemical is released from the inside and it flows out over all the surfaces it touches, this means the irons tip, the PCB, the wire etc. You can see the left over flux around a joint on a PCB.

If you are making some important mission critical high reliability equipment, sure stick to the standards to avoid any unnecessary liability. If not then just look at your solder joint under a inspection microscope. If the joint looks good and is shiny then its going to work just fine. If the joints don't look nice then tweak your soldering process until they do look good. Apply the solder at a different spot on the joint, heat for a different amount of time, use different solder type, add liquid flux separately if needed etc... All of this will have a much bigger effect on the finished joint than just cutting solder.

In general there is never too much flux when it comes to soldering. The more flux you slap on there the better it solders. The reason why we don't tend to just dunk whole board into a vat of flux is because the stuff should be cleaned off afterwards, so you don't want to use more than you need to avoid unnecessary cleanup. (Well they do tend to spray whole boards with flux in wave soldering, but that's a different process)

[coppercone2]

how reliable is the shiny joint test that people keep talking about?

What is the chance of cracks or other subsurface effects (subsurface oxide being pulled in mechanically?)

i.e. when I melt lead for castings, if you melt a bunch and you give it a good stir, stuff comes up. To get a nice pure casting it seems almost be a requirement to stir it like a witches cauldron. I almost feel like for high quality casting work you would need to put a non reactive inert gas bubbler into the lead melter just to stir the crap up.

When I mean stir I mean gentle stir, like dropping a steel rod into it and gently dragging it around without turbulence. Before I did it my first time I thought the density difference would just make everything come right up, but I find myself skimming dross several times with stirring to get a clean pour. 

[IanB]

how reliable is the shiny joint test that people keep talking about?

What is the chance of cracks or other subsurface effects (subsurface oxide being pulled in mechanically?)

If it looks good, it is good. Again, you are overthinking this. If you are employed to solder to appropriate, high reliability standards, then you will undergo training and certification to ensure you can work to the required standard. You make no mention that you are being trained or certified, therefore you are working to informal standards and you just need to make sure your work has the correct appearance when you have finished.

i.e. when I melt lead for castings, if you melt a bunch and you give it a good stir, stuff comes up. To get a nice pure casting it seems almost be a requirement to stir it like a witches cauldron. I almost feel like for high quality casting work you would need to put a non reactive inert gas bubbler into the lead melter just to stir the crap up.

When I mean stir I mean gentle stir, like dropping a steel rod into it and gently dragging it around without turbulence. Before I did it my first time I thought the density difference would just make everything come right up, but I find myself skimming dross several times with stirring to get a clean pour.

This is not "almost" a requirement, it is definitely a requirement. To make good quality castings the process should include both the use of a degassing step and addition of flux to the melt. It should also include accurate temperature control with a thermometer.

[Berni]

Yes this is exactly why everything needs to be kept clean when soldering.

Oxides and other crap mess things up. This is why its important to have your joint clean before you start and have a clean soldering iron tip. The flux can only eat up the crud so quickly and its only meant to remove the tiny bit of surface corrosion that happens from the metals sitting in air.

Best method of preparing metals for soldering is abrasion to expose fresh new metal underneath. Like the good ol sandpaper rub of copper pipes before soldering. But since this is not practical in electronics what is done instead is coating the copper in a more oxidation resistant metal. This is the reason for gold or tin plating or HASL on PCBs. The nice wires are also tin or silver plated to make them easier to solder. leads of components are commonly plated in tin or silver. That way surfaces are kept mostly free of oxide all the way until the soldering process.

It still is possible for a good looking solder joint to be bad if it was done with the wrong soldering technique. This is usually caused by not getting both sides of the joint hot enough for the solder to properly flow. So as long as whoever is soldering has a good deal of experience then a good looking joint should always be 100% good. Things like cracks and such don't develop during soldering but actually develop later on if too much repetitive stress is put on the joint or its exposed to excessive thermal cycling.

[coppercone2]

I was imagining something like a fault line of oxide that makes a weak area in the solder joint so its deceptively strong considering its size, so its almost like necked down in terms of metal that can withstand strain forces

[IanB]

Solder won't form a fracture in the middle of a joint unless you move it in the plastic stage before it has solidified. Where the joint will usually be faulty is at the interface between solder and the parts being joined. For example, if the solder doesn't properly wet the lead of a through hole part it will ball up and make a donut shape instead of forming a neat cone. Similarly, if the solder doesn't adhere to the solder pad it will ball up and make a globule above the surface.

If you have a nice properly formed cone or fillet with smooth edges and shiny surface there will not likely be anything wrong inside it.

[KL27x]

i.e. when I melt lead for castings, if you melt a bunch and you give it a good stir, stuff comes up. To get a nice pure casting it seems almost be a requirement to stir it like a witches cauldron. I almost feel like for high quality casting work you would need to put a non reactive inert gas bubbler into the lead melter just to stir the crap up.

You can whip up as much dross as you want. You will never stop making more, because the surface is producing more oxides. You can do that until all your lead is gone. You probably don't need to stir it as much as you think. Unless there's zinc contamination, just about any other contaminate does separate out quite easily. You just have to skim it, again, right before you pour it. If you use a bottom pour pot, you can leave a layer of flux and dross on top of the pot and pour clean castings for minutes or hours at a time.

When you solder a PCB, you are starting with clean lead alloy. The surface might oxidize, but that is where the flux acts. All that oxidized solder ends up in the flux residue. It's the white bits (lead and copper and tin salts) that are left after you dissolve the resin with alcohol.

Its simply a chemical that once heated to a certain temperature becomes really reactive and begins forcefully ripping oxygen atoms out of anything it comes in contact with. This removes oxide layers off metal surfaces.

If only. Metal oxides can be reduced back to metal. But the main way that flux removes oxides is by combining acid and metal oxides to make metal salts. You're largely removing the metal oxides and forming dross/salts, not reversing/reducing the oxides back to base metal.

As long as the flux has enough resin and/or you clean the board, the bits of salts are not a problem. They don't contaminate the solder bead. They are pushed out to the surface of the solder. If the oxides cause a problem, it's through loss of surface tension/mobility and the result will be poor wetting, poor thermal transfer, and a lumpy-bumby appearance of the bead.

[coppercone2]

I agree that dross keeps accumulating, but there seems to be alot more of it for the first 2-3 stirs then subsequent ones

[KL27x]

Exactly. If you start with reasonably clean alloy*, it only takes a spoon of borax or wax or sawdust per 10-20 lbs and a few seconds of stirring to clean the entire pot. Scrape the sides of the pot, especially, because this is where any contamination will probably come from. Every time you stir, you expose clean lead at the surface, and a new skin of oxide forms very quickly. 

First time I casted with lead, I kept fluxing and stirring, wondering when it would be clean, and I wasted probably several pounds of lead. Leave the skin alone until just before you pour. If you use a bottom pour pot, just leave the skin and/or a layer of flux residue alone.

If you notice crud/scale building up on the surface of the pot, after you empty it, you can wash it out with vinegar.

*I hope you aren't melting down dead car batteries without taking special precautions. They contain cadmium, and the fumes are toxic.

[coppercone2]

rofl melting down car batteries into shop tools, thats like bangladesh or something

[KL27x]

And the kettle calls the pot black. Some of the things you have admitted to doing to save a few pennies is worse than anything I imagine going down in Bangladesh!

Here's my perception of you in a nutshell, based on your posts.

[coppercone2]

whats the Ra on your crack pipe buddy?

[eKretz]

I must admit to laughing when I read the comic. Not that I have ever thought about CC's posts that way.  Ahem.

Anyway, a good pair of very sharp cutters will indeed cut multicore and leave the cores perfectly exposed. I tested mine this way when I sharpened them. That said, a dull pair will probably pinch them shut and crush the solder.