Best soldering flux?

[Shrek]

I am finding devices failing due to dry solder joints (most recently a USB 3 hub) and so far I have been using Kester 186 soldering flux for reflowing; I also ordered some RadioShack flux as it has stella reviews, but was wondering what people here felt was the best flux for reflowing.

I like no-clean although I normally scrub with isopropyl alchohol.

 

[Arctucas]

I have not used paste for many years. I just use rosin-core silver solder for doing electrical/electronics work.

 

[Bones]

I use ruby fluid for what I do.

 

[Shrek]

I have not used paste for many years. I just use rosin-core silver solder for doing electrical/electronics work.

That is why I asked, the connectors can be small and densely populated, so I tend to be reluctant to add new solder; but rather just add flux and apply a soldering iron to what is already there.

I use ruby fluid for what I do.
View attachment 238837

This seems to be too corrosive for circuit boards.

 

[Bill_Bright]

Ummm, "dry" solder joints are simply solder joints that don't have enough solder in them. They are not caused by poor flux. They are caused by poor soldering techniques.

The purpose of flux is to clean and prevent oxidation during the soldering process. Even with the best flux, you can still have a dry joint due to not enough solder, or a cold joint due to improper application of heat.

Flux can "help" prevent cold joints caused by impurities and oxidation - but not always. And soldering is a skill. And like all skills, they must be practiced and the technician must stay in practice. And then, regardless how skilled, each joint should be inspected.

 

[xrobwx71]

I have used the SRA paste with good results.

 

[Shrek]

Ummm, "dry" solder joints are simply solder joints that don't have enough solder in them.

Then what to call a joint that has sufficient solder but where the solder has not wetted the lead but is still in contact?

While I was fortunate that my repair using Kester 186 and no extra solder (I didn't want to deal with cross-connections) worked, I anticipate this will not be the last time I do such repairs so thought to ask what flux to get when my small bottle of Kester 186 runs out. Perhaps I should have asked what the best flux with an indefinite shelf life is.

 

[Ferrum Master]

There are no best.

I use Stannol MULTIFIX 450-01 for rework.

Official regulations are forcing to use fluxpens, that I am not fond off... but oh well...

 

[Bill_Bright]

Then what to call a joint that has sufficient solder but where the solder has not wetted the lead but is still in contact?

It is when there is not enough solder where it needs to be.

I am not going to get into another back and forth with you, Andy.

A dry joint is due to poor soldering technique.

 

[Shrek]

I've also wondered about making my own soldering flux, which might be fun, but probably not worth the trouble.

DIY solder flux with rosin and alcohol - Bing video

 

[Ferrum Master]

I've also wondered about making my own soldering flux

DIY solder flux with rosin and alcohol - Bing video

Andy... people did stuff like that during cold war... because of poverty, get a proper Flux from a reputable maker, those are not cheap, but they perform miles better than your homebrews with some random alcohol leaving unknown residue behind. Due to the fact it is alcohol, you don't fully warm up to fully react the rosin, thus it may be left chemically aggressive.

I always thought dry joints are the thing you get when you get older...

Cold joint is another topic tho.

 

[Bill_Bright]

If you want to minimize the chances of having a bad soldering joint, practice. Instead of discarding or selling your old motherboard or graphics cards, keep them. Then used them to practice removing and replacing the components.

Of course, quality tools are the mark of the good craftsman too. Use a good iron.

 

[Shrek]

I use a Weller iron (W60P) that regulates the temperature using the Curie effect from a magnet that is at the back of the tip. I also inspect the joints with a strong magnifying glass, but even then, it is hard to catch a joint that is not fully wetted.

Anyhow, the hub repair was a success; I am just anticipating the next such repair.

 

[Ferrum Master]

I use a Weller that controls the tip temperature using the Curie effect from a magnet that is part of the tip.

Weller or not, it doesn't magically make you better at the task. It is all about experience. I could solder without an issue with anything... even a glowing red nail...

Quality Flux is a must. Just search for your local brands. The shown examples of round containers are not really recommended. You can solder some wires with it, but those are aggressive and can leave afterward even conductive salts and is a bitch to clean. Cleaning solvents must be usually paired with the flux you use.

 

[Shrek]

I have been using Kester 186 which seems to clean off well with isopropyl alcohol, although it does not need removing.

I paid top dollar for the RadioShack flux even though it comes in a round container.

 

[Bill_Bright]

Quality Flux is a must.

I agree. But quality does NOT mean you need the absolute best (whatever that means) out there. Quality just means it is not not full of impurities, and it does its job of cleaning and preventing oxidation. The rest is up to the skills of the tech.

 

[Bones]

This seems to be too corrosive for circuit boards.

It's not, been using it too long with good results for it to be or I'd just stop using it.
And it's not like you're going to apply it and leave it on overnight for such an effect to happen anyway, you use it as you do the work.

 

[Ferrum Master]

I have been using Kester 186 which seems to clean off well with isopropyl alcohol, although it does not need cleaning.

I paid top dollar for the RadioShack flux even though it comes in a round container.

The usual fake ones? The fake one smells like burned Vaseline and leaves brown residue.

Even the original is way too runny and not too activated for my taste, but that's pretty subjective.

But quality does NOT mean you need the absolute best

The ones that figured up earlier in the thread were absolute crap.

And it's not like you're going to apply it and leave it on overnight for such an effect to happen anyway, you use it as you do the work.

If you solder some MCU, it soaks it in, also in the cleaning process. The aftermath of that is that the darn thing will hang up more often and do some random things.

 

[Shrek]

Even the original is way too runny and not too activated for my taste, but that's pretty subjective.

One reason I ordered the RadioShack paste, but runny is good if one wants to get flux under a GPU chip for reflowing.

The other issue was the finite shelf-life although what I have seems to still be fine.

 

[Ferrum Master]

One reason I ordered the RadioShack paste, but runny is good if one wants to get flux under a GPU chip for reflowing.

I recommended you a no-clean flux... while that RadioShack says it must be cleaned. While both of them must be cleaned either way, the RadioShack one politely tries to say that it leaves chemically aggressive and even possibly conductive salts after the soldering.

 

[Bones]

The usual fake ones? The fake one smells like burned Vaseline and leaves brown residue.

Even the original is way too runny and not too activated for my taste, but that's pretty subjective.



The ones that figured up earlier in the thread were absolute crap.



If you solder some MCU, it soaks it in, also in the cleaning process. The aftermath of that is that the darn thing will hang up more often and do some random things.

I've never had issues with what I use with anything (Yet) and that's why I use it.
From tiny MOSFETs to whatever else it works and that's why I have it and use it as I do, it's not crap and has been around for years.
I admit for some it's probrably not available to get or whatever else such as there is a cheaper brand that works just as well available and that's OK, I'm not knocking anyone for using what they prefer.

All I can really say is if it works for you, just go with it.

 

[Shrek]

I recommended you a no-clean flux... while that RadioShack says it must be cleaned. While both of them must be cleaned either way, the RadioShack one politely tries to say that it leaves chemically aggressive and even possibly conductive salts after the soldering.

Good point, and while I always clean after, it is better to use no-clean flux; but I am willing to go with 'needs cleaning' if I need a more aggressive flux, and the last repair seemed like it would have benefited from a flux somewhat more aggressive than Kester 186

I want my repairs to not just work, but last decades.

For some reason I have not even considered water soluble fluxes.

 

[Ferrum Master]

I've never had issues with what I use with anything (Yet) and that's why I use it.
From tiny MOSFETs to whatever else it works and that's why I have it and use it as I do, it's not crap and has been around for years.
I admit for some it's probrably not available to get or whatever else such as there is a cheaper brand that works just as well available and that's OK, I'm not knocking anyone for using what they prefer.

All I can really say is if it works for you, just go with it.

I work daily for 20 years with those things. If you don't notice the damage, it doesn't mean there ain't one.

If you rise up your bar into MCU, high frequency radios, things start to get conductive that are not in brute electronics, like simple power supplies, where it ain't that critical. You cannot wash a PCB using plain domestic alcohol, as it was being held in aluminum tanks, it contains metal ions. How techs pinpointed that? Easy, during early 2000 washing water damaged mobile phones. And that's an early blunt tech. After washing the PCB soaked up and started to conduct. We just put the PCB on hotplates and removed every component and measured power lane resistance versus an unwashed one. The board itself started to conduct and later pinpointed the cause.

Good point, and while I always clean after, it is better to use no-clean flux; but I am willing to go with 'needs cleaning' if I need a more aggressive flux, and the last repair seemed like it would have benefited from a flux somewhat more aggressive than Kester 186

Look up in the datasheets. I am still trying to understand what kind of property are you still trying to fix... just use a wick and remove the lead free solder and put the lead containing one. When you are repairing stuff, you have lead free solder in front of you. Higher temperatures. You solder usually with lead containing solder, that's more friendly to use and has lower temps and causes less stress to the PCB and components.

 

[Shrek]

You are right, I have braid and could have removed the lead-free stuff, but I didn't want to risk exposing the board to too much heat; my intuition told me to use flux and reflow the old lead-free solder such that the joint was fully wetted.

Infact, I agree with you when you say

• Needs the right tools
• Needs the right experience

but feel that experience includes knowing how to approach the problem and no I am not saying my approach was the right one.

 

[Ferrum Master]

You are right, I have braid and could have removed the lead-free stuff, but I didn't want to risk exposing the board to too much heat. My intuition told me to use flux and reflow the old lead-free solder such that the joint was fully wetted.

Use a preheater or hotplate. Heat up the board to around 80-100C and then do the soldering at top. Without preheat, it is way to hard for properly designed multi layer PCB. As you see, there are ground plane vias that act as a heatsink, you always have to consider the medium you are soldering and adjust the temperatures and power you apply to joint.

Without preheating... it will end up as Bill warned.