Solder paste doubt

[DeusM]

First of all don't know if this is the right place to ask this. I bought a Pro'skit solder paste because I saw a video about how to remove a component and they used solder paste for that. Also, because they used it in cables before soldering for a better results. Reading about solder paste and flux and also about the product I have, I'm pretty sure its flux (maybe all solder paste are flux? Still pretty confuse about it). Also, I read about people applying it into the PCB before and after soldering for better results (the flux, not the paste I have) Many people also say it's not necessary if you are good soldering but I'm not 
My question is: Can I use this paste in a PCB before and after soldering for better connections as with the flux? I'm aware you have to let it dry and then clean it with proper alcohol to remove impurities.

Hope someone can help me understand all of this a little better.



Here is a picture of the solder paste

[anotherjim]

Haven't tried that, but
Unless it's terrible mislabelling, it should be flux mixed with finely ground solder. If it were just flux, it should be called flux.
Found this description..

Our soldering paste is composed of metal powder activated flux and blending agents. The area and thickness to be soldered can be easily controlled. No spot appears in non-soldered area. The paste has a good diffusion and non-corrosion.

Melt some with an iron or whatever -  does it leave blobs of solder?
Label warnings suggest the flux content leaves a partially conductive residue?

[Kipper4]

It looks more like the active flux I use for soldering copper pipe than anything I'd use with a pcb.
Hmmmm

[slacker]

That's what I thought too Rich, if you google it some of the descriptions call it acid flux which fits with that as well. There's talk of using it for desoldering though so who knows.

[wavley]

"This solder paste is not suitable for the soldering point of Integrated Circuit or high voltage (frequency/power)"

[Ice-9]

That just looks like plumbers flux.

[DeusM]

So I guess I bought something that's useless for soldering components or cables. What a drag, it costed me a lot of money (I'm from Argentina btw so excuse me if I have some typos or write something wrong :p). So what type of flux do you recommend me to use? I know that tin has come flux inside but I found a lot of trouble when soldering guitar cables. And what about using it before and after soldering on the pcb? (not this soldering paste but the flux)

[PRR]

> maybe all solder paste are flux?

The only sure-safe flux for electronics is tree rosin, often "activated". But non-rosin fluxes are also "activated", which can mean anything.

Pro'skit 8S005 is "acid-free" Plumber's flux. Use it on pipes, NOT small wires.

http://www.unionrepair.com/index.php?dispatch=attachments.getfile&attachment_id=8

Composition / information on ingredients:
Hazardous Ingredient Name WT% C.A.S. Number Organic Standard
Petrolatum 75 8009-03-8 Not Applicable
Zinc Chloride 15 7646-85-7 Not Applicable
Water 10 7732-18-5 Not Applicable

"Petrolatum" was originally gunk on the first oil-wells. Drillers used it to cover wounds and burns. A purified form has been sold widely as "Vaseline" brand ointment.

Zinc Chloride is useful to loosen oxide on hot metal such as soldering. However:

"Because of its corrosive nature, this flux is not suitable for situations where any residue cannot be cleaned away, such as electronic work."
https://en.wikipedia.org/wiki/Zinc_chloride#As_a_metallurgical_flux

When my dad worked in the computer factory (mainframe), possession of "plumber's flux" on the job was grounds for instant dismissal. The joint would work a few months until the harsh flux ate-through the fine wires. This of course happened at the Customer's site, making a VERY unhappy customer.

Less a problem on pipes or roofs because the gauge is much heavier. And because solder pushes the flux out of the tubular joint to where it can be wiped away.

Zinc Chloride is made by dropping Zinc in acid until it stops bubbling. It is possible the worst old fluxes still had acid in them. Maybe modern chemistry really has got the acid out. I would NOT bet my work on it.

I have seen some YouTube video showing this brand/model flux used for SMT parts. This is just stupid. Rosin flux in alcohol For Electronics is readily available and known safe.

[Ice-9]

So I guess I bought something that's useless for soldering components or cables. What a drag, it costed me a lot of money (I'm from Argentina btw so excuse me if I have some typos or write something wrong :p). So what type of flux do you recommend me to use? I know that tin has come flux inside but I found a lot of trouble when soldering guitar cables. And what about using it before and after soldering on the pcb? (not this soldering paste but the flux)

I think it is solder you need not flux. The easiest solder to use is a leaded solder which usually has a lower melting point than non leaded which makes it easier to solder larger wire like guitar cables if you soldering iron is only a small one.
Flux for electronics is available in a small pen format but you should not need that if your solder is the correct type with flux already in the core of the solder. The flux pens are best for re soldering and also SMD work.

Solder PASTE on the other hand I use for SMD work mostly and looks like silver paste and is also VERY expensive for good quality stuff, the solder paste is a mix of solder  and flux.

In the UK
lead/tin solder is about £17  for a 500g roll.
Good solder paste about £75 for 500g
No Clean flux pen about £7

[DeusM]

Ok. So first of all I read some reviews again and I noticed that all state that it's non corrosive. Here is a video of a guy using it to desoldering: https://www.youtube.com/watch?v=XKj1-24_7Ts
It's a pretty bad video but it gets to the point. The way I use it nevertheless is putting some solder paste in a woolen metal sponge so it absorbs the melted solder and it worked really well for me.



This type of sponge btw:



Second: I DO USE SOLDER! I took a couple of pictures but I couldn't get any good quality image so there's no point in doing that.

It leaves some residue in the sides but the solder... It looks so good to me. It's very shiny and looks so well melted and bonded with the wire and the jack. It even took the form of the small filaments of the wires. So. I don't know. If the joints last, I will continue using it for repairing cables. Not so sure about soldering components into a pcb because of the residue, although many people seem to have the same problem with flux and cleaning it too.

[DeusM]

Also, it says its not suitable for integrated circuits or high voltage but I don't think 9v is high voltage right? And maybe its not SUITABLE for integrated circuits because they tend to brake when it heats and also the solder goes everywhere?

[anotherjim]

Yes, I noticed it does claim to be non-corrosive.
There is a common factor between IC and HV work - isolation -  IC's are mostly sensitive to leakage current thru any residual goop around the pins, while for high voltage it's fairly obvious that nothing must reduce the insulation around parts. I suspect it cannot be guaranteed that you can clean the flux residue sufficiently.
It was our "Cloudscapes" who had a problem with a uPC crystal clock failing due to flux residue in a thread last year?

[armillary]

Sure, even standard rosin-core solder can cause problems. In a service manual for Moog products using 1458, 741 and other types of op amps, the schematics include the caution, "Replacement of any component must include removal of all solder flux to avoid leakage of high impedence circuits."

In my case, a newly replaced 1458 in a key trigger circuit was always on as if one of the keys was pressed. Eventually the problem was solved by cleaning up the repair with flux remover on a q-tip.     

[amptramp]

It was a normal practice for many years in military electronics to clean off all soldered connections with trichloroethane so there would be no flux residue left at all.  I doubt they still use the same chemicals due to toxicity, but flux should be removed where possible if humidity or high impedances are involved.  Still, a lot of Heathkit equipment got built without removing flux and it worked without trouble.

[duck_arse]

we'd call that "steel wool". I wouldn't have thought it would work as solder wick, but I suppose if it was all fluxed up, it would wick hot solder as well as tinned copper braid.

[greaser_au]

It was a normal practice for many years in military electronics to clean off all soldered connections with trichloroethane so there would be no flux residue left at all.  I doubt they still use the same chemicals due to toxicity, but flux should be removed where possible if humidity or high impedances are involved.  Still, a lot of Heathkit equipment got built without removing flux and it worked without trouble.

We used a Freon in the vapour cleaner for cleaning flux off prior to coating. One day we trialled the much cheaper tri-nu (1,1,1 triclorethylene) in the unit and it was extremely effective...  until a batch of 8 double eurocards went in with two 96-pin connectors on each. the plastic connector shells turned to runny goop...   guess which bunny was the rework/repair operator  at the time 

From the vids of this stuff, it just looks like flux or maybe a high temperature grease/oil to exclude air, so it would be a "soldering paste",  rather than "solder paste"

david

[Ice-9]

Ok. So first of all I read some reviews again and I noticed that all state that it's non corrosive. Here is a video of a guy using it to desoldering: https://www.youtube.com/watch?v=XKj1-24_7Ts
It's a pretty bad video but it gets to the point. The way I use it nevertheless is putting some solder paste in a woolen metal sponge so it absorbs the melted solder and it worked really well for me.



This type of sponge btw:

Ok lets clear this up, It is NOT solder paste, it IS flux paste only. You cannot solder with this stuff alone, but you can de solder, a no-clean flux pen is better.



Second: I DO USE SOLDER! I took a couple of pictures but I couldn't get any good quality image so there's no point in doing that.

It leaves some residue in the sides but the solder... It looks so good to me. It's very shiny and looks so well melted and bonded with the wire and the jack. It even took the form of the small filaments of the wires. So. I don't know. If the joints last, I will continue using it for repairing cables. Not so sure about soldering components into a pcb because of the residue, although many people seem to have the same problem with flux and cleaning it too.