Author Topic: Looking to buy some flux (pen+paste)  (Read 3814 times)

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Offline l3gi0nTopic starter

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Looking to buy some flux (pen+paste)
« on: October 10, 2021, 09:05:08 pm »
I am a beginner and I am looking to buy a flux pen and a flux paste. I have looked at two options:

https://www.amazon.ca/gp/product/B008OC0E5M/ref=ox_sc_act_title_1?smid=A1FSCB8N4XVP5G&th=1

+

https://www.amazon.ca/gp/product/B008ZIV85A/ref=ox_sc_saved_image_4?smid=A1FSCB8N4XVP5G&psc=1


Are these good for a beginner ? Or should I go for the slightly more expensive MG chemical equivalents ?
 

Offline Benta

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Re: Looking to buy some flux (pen+paste)
« Reply #1 on: October 10, 2021, 09:52:15 pm »
Why?
I've worked with electronics for decades, and have never needed this. Why do you need flux?

 

Offline ElizatronicWarfare

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Re: Looking to buy some flux (pen+paste)
« Reply #2 on: October 10, 2021, 09:55:42 pm »
Are you serious? Flux is a vital part of soldering, as it chemically separates oxides and other slag from the liquid metal. Most modern solders come with a flux core as standard, but sometimes extra flux is required for particularly nasty joints (such as repairing/reflowing an old or poor-quality joint).
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Offline l3gi0nTopic starter

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Re: Looking to buy some flux (pen+paste)
« Reply #3 on: October 10, 2021, 10:08:17 pm »
Do I really need both the pen and the paste both ?

I am trying to solder a FPC connector to a PCB...Should I get the pen, paste or both ?
 

Offline Benta

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Re: Looking to buy some flux (pen+paste)
« Reply #4 on: October 10, 2021, 10:09:54 pm »
Are you serious? Flux is a vital part of soldering, as it chemically separates oxides and other slag from the liquid metal. Most modern solders come with a flux core as standard, but sometimes extra flux is required for particularly nasty joints (such as repairing/reflowing an old or poor-quality joint).

I'm sure you're right when it comes to plumbing and drains.
As I said, I've never (over 40+ years) needed extra flux in electronics.

 

Offline Benta

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Re: Looking to buy some flux (pen+paste)
« Reply #5 on: October 10, 2021, 10:14:59 pm »
Do I really need both the pen and the paste both ?

I am trying to solder a FPC connector to a PCB...Should I get the pen, paste or both ?

If it's through-hole, you use an electronics solder that already contains flux in the core.
If it's SMD, you use a solder paste that contains flux.

Extra flux is in neither case helpful nor desirable.
 

Offline Kleinstein

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Re: Looking to buy some flux (pen+paste)
« Reply #6 on: October 10, 2021, 10:19:34 pm »
For SMD part with normal solder (no paste) one sometimes needs extra flux. It is no just to clean oxidized surfaces, but it also help the solder to flow better and avoid brigdes on finer SMD part (e.g. MSOP).  One does not not both forms of flux, but one form of extra flux can be really handy.
 
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Offline xavier60

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Re: Looking to buy some flux (pen+paste)
« Reply #7 on: October 11, 2021, 12:01:55 am »
I started using DeoxIT branded flux a few months ago. It works well with no leakage problems.
https://www.jaycar.com.au/solder-flux-paste-56g-tub/p/NS3070
I dispense it from a syringe fitted with a dispensing needle.
The syringes that have no rubber bung work best, https://www.chemistwarehouse.com.au/buy/57259/disposable-syringe-5ml-luer-slip
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Offline tooki

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Re: Looking to buy some flux (pen+paste)
« Reply #8 on: October 11, 2021, 12:56:35 am »
Do I really need both the pen and the paste both ?

I am trying to solder a FPC connector to a PCB...Should I get the pen, paste or both ?

If it's through-hole, you use an electronics solder that already contains flux in the core.
If it's SMD, you use a solder paste that contains flux.

Extra flux is in neither case helpful nor desirable.
Those are not the only kinds of soldered joints in electronics.

Some soldering techniques, like drag soldering, categorically cannot be performed without external fluxing, because you aren’t bringing either wire solder nor solder paste to the joint. It’s also essential for SMD repair. For other types, it’s optional, but often helpful. (Like if a component is older and its leads have tarnished.)

Maybe educate yourself on the advances that have happened in the last 40 years before barging in with broad proclamations that are actually wrong.

And to say it’s neither helpful nor desirable is wrong too: extra flux never hurts, other than being more to clean up. But the joints will never suffer for it, and will often be superior.
« Last Edit: October 11, 2021, 01:03:18 am by tooki »
 
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Offline tooki

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Re: Looking to buy some flux (pen+paste)
« Reply #9 on: October 11, 2021, 01:01:01 am »
I am a beginner and I am looking to buy a flux pen and a flux paste. I have looked at two options:

https://www.amazon.ca/gp/product/B008OC0E5M/ref=ox_sc_act_title_1?smid=A1FSCB8N4XVP5G&th=1

+

https://www.amazon.ca/gp/product/B008ZIV85A/ref=ox_sc_saved_image_4?smid=A1FSCB8N4XVP5G&psc=1


Are these good for a beginner ? Or should I go for the slightly more expensive MG chemical equivalents ?
Both of those are fine.

If you only get one, get a tacky/gel flux. (Rather than liquid or a thick paste like in the tubs.) The nicest flux I’ve found so far is the ChipQuik SMD291NL. It works great, it has a fantastic consistency, and unlike the acrid smoke given off by every other modern flux, it smells of toasted hazelnuts. And it’s not particularly expensive.
 

Offline xavier60

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Re: Looking to buy some flux (pen+paste)
« Reply #10 on: October 11, 2021, 01:09:18 am »
To be avoided are fluxes that either immediately cause current leakage or leave residues that  absorb moisture causing leakage problems later. A Chipquick branded flux that I tried, caused immediate leakage that remained after the PCB was cleaned. It gradually came good on its own. 

Extra: It actually is SMD291, there is possibly no problem when used to reflow SMD rather than for hand soldering.
« Last Edit: October 11, 2021, 01:18:51 am by xavier60 »
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Offline tooki

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Re: Looking to buy some flux (pen+paste)
« Reply #11 on: October 11, 2021, 01:18:41 am »
To be avoided are fluxes that either immediately cause current leakage or leave residues that  absorb moisture causing leakage problems later. A Chipquick branded flux that I tried, caused immediate leakage that remained after the PCB was cleaned. It gradually came good on its own.
They make many different fluxes, including ones that require proper cleaning.

The SMD291NL I mentioned is a no-clean flux, so should be entirely safe if used for reflow soldering, or if cleaned after hand soldering.
 

Offline agehall

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Re: Looking to buy some flux (pen+paste)
« Reply #12 on: October 12, 2021, 05:53:46 am »
Since OP is in Canada, I'd suggest getting some AmTech flux. I've tried several other brands but nothing else seems to work as well. The ChipQuick stuff I've tested just burns and turns nasty even at fairly low temps (~250C). AmTech NC-559-V2-TF is my goto flux for almost everything these days.
 

Offline james_s

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Re: Looking to buy some flux (pen+paste)
« Reply #13 on: October 12, 2021, 07:21:51 am »
If it's through-hole, you use an electronics solder that already contains flux in the core.
If it's SMD, you use a solder paste that contains flux.

Extra flux is in neither case helpful nor desirable.

I beg to differ. Extra flux is absolutely essential for hand soldering fine pitch SMD stuff, try soldering a 0.5mm pitch QFP or FPC connector with a soldering iron without extra flux, good luck with that. It's also very useful for removing stubborn solder bridges on fine pitch stuff and desoldering wick works immensely better when dipped in liquid flux. I'm not sure how you could do electronics for decades without flux, unless you never hand solder and rework SMD stuff.
 
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Offline tooki

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Re: Looking to buy some flux (pen+paste)
« Reply #14 on: October 12, 2021, 10:29:08 am »
The ChipQuick stuff I've tested just burns and turns nasty even at fairly low temps (~250C).
ChipQuik makes many different fluxes, but the company’s specialty is super-low-temperature products. Are you sure you didn’t accidentally get one of those specialty low-temp fluxes? I wouldn’t be surprised if it burned up at normal soldering temperatures, since it’s intended for use at far lower temperatures.

Their fluxes for (non-low-temp) lead free soldering absolutely have no trouble with normal lead-free soldering temperatures. I typically use it at around 330C for lead-free.
 

Offline cgroen

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Re: Looking to buy some flux (pen+paste)
« Reply #15 on: October 12, 2021, 12:16:25 pm »
..
If it's through-hole, you use an electronics solder that already contains flux in the core.
If it's SMD, you use a solder paste that contains flux.

Extra flux is in neither case helpful nor desirable.

Oh boy, I would NOT want to try and solder QFP or a FPC connector WITHOUT extra flux, especially if doing drag-soldering of it (regardless of the soldering done, you need the extra flux)  :-\
There is NO way this will end well if not used.
 
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Offline agehall

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Re: Looking to buy some flux (pen+paste)
« Reply #16 on: October 12, 2021, 01:52:28 pm »
The ChipQuick stuff I've tested just burns and turns nasty even at fairly low temps (~250C).
ChipQuik makes many different fluxes, but the company’s specialty is super-low-temperature products. Are you sure you didn’t accidentally get one of those specialty low-temp fluxes? I wouldn’t be surprised if it burned up at normal soldering temperatures, since it’s intended for use at far lower temperatures.

Their fluxes for (non-low-temp) lead free soldering absolutely have no trouble with normal lead-free soldering temperatures. I typically use it at around 330C for lead-free.

Yeah, I'm pretty sure I didn't try any low temp stuff. Maybe I've managed to avoid their good stuff, but I've tried 3 or 4 different ones and none of them gave even close to the performance I see with AmTech, so I've given up on them.
 

Offline james_s

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Re: Looking to buy some flux (pen+paste)
« Reply #17 on: October 12, 2021, 05:01:21 pm »
I've been using two different types of Amtech flux, one I'm suspicious of because it came direct from China but the other was recently expired stuff from a US seller so I'm pretty sure it's genuine. Both work just fine though, one is water washable but you HAVE to wash it because it's conductive and the other is a more conventional rosin flux. I have found applications for both.
 

Offline ledtester

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Re: Looking to buy some flux (pen+paste)
« Reply #18 on: October 12, 2021, 06:00:03 pm »
I have the SRA pen flux and it's fine. I think you'll find the hockey puck flux hard to use because you have to use an applicator to apply it and then you'll have to clean your applicator. I'd go for a flux in a syringe tube.

Amtech flux comes highly recommended, especially their "559-V2" product (NC-556-V2-TF). The cheapest place I've found to get it is from Louis Rossman:

https://store.rossmanngroup.com/amtech-nc-559-v2-30-cc-16160.html

who for some reason is selling it at 1/2 the price as everyone else.

Of course, be wary of the "Amtech" flux you can get on aliexpress/ebay. On the other hand, there are some youtube videos that say that those fluxes work ok.

Look up some youtube videos on the Amtech flux and you'll get a feel for how it is used.
 

Offline l3gi0nTopic starter

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Re: Looking to buy some flux (pen+paste)
« Reply #19 on: October 12, 2021, 06:35:22 pm »
I went with the RA SRA flux : https://www.amazon.ca/gp/product/B008ZIV85A/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

Because RA flux works better.

I see no reasons to buy two types of fluxes...the RA SRA puck would do..  I will use a toothpick to apply the flux...but I am wondering how to clean the RA flux residue ? My understanding is that I should apply IPA 99% and then use a swab to clean the board etc ? what if flux gets under the components and the swab cannot reach them ?

I also ordered this IPA: https://www.amazon.ca/gp/product/B005T8PL1Q/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
« Last Edit: October 12, 2021, 06:48:57 pm by l3gi0n »
 

Offline ElizatronicWarfare

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Re: Looking to buy some flux (pen+paste)
« Reply #20 on: October 13, 2021, 06:25:51 am »
Flux left behind in nooks and crannies is not an issue, unless you are working with radio frequencies where it will interact strangely with the electromagnetic fields.
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Offline xavier60

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Re: Looking to buy some flux (pen+paste)
« Reply #21 on: October 13, 2021, 06:52:38 am »
I went with the RA SRA flux : https://www.amazon.ca/gp/product/B008ZIV85A/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

Because RA flux works better.

I see no reasons to buy two types of fluxes...the RA SRA puck would do..  I will use a toothpick to apply the flux...but I am wondering how to clean the RA flux residue ? My understanding is that I should apply IPA 99% and then use a swab to clean the board etc ? what if flux gets under the components and the swab cannot reach them ?

I also ordered this IPA: https://www.amazon.ca/gp/product/B005T8PL1Q/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
RA is supposed to be more active than RMA. I tested the DeoxIT flux with an insulation tester. There was some leakage only while being heated.
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Online Ian.M

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Re: Looking to buy some flux (pen+paste)
« Reply #22 on: October 13, 2021, 07:36:22 am »
Flux left behind in nooks and crannies is not an issue, unless you are working with radio frequencies where it will interact strangely with the electromagnetic fields.
I beg to differ.

Flux residue is generally fairly non-conductive so any interactions with RF EM fields are generally due to its dielectric effect.  Unless you are working with microwave frequencies high enough to need special PCB material or with high voltage or high power PAs, you are very unlikely to get any issues from residue that also isn't grossly visibly unacceptable.

However flux residue can be more generally harmful - apart from board corrosion leading to eventual failure, it can cause high surface leakage, resulting in problems with high impedance and low noise circuits at any frequency from DC upwards.

Rosin R and RMA flux* remnants that have been heated sufficiently to drive out volatiles and fully activate the flux rarely cause corrosion issues, unless the resin component has been dissolved leaving metal salts behind by improper cleaning.  Rosin RA flux residue can be corrosive, especially if any of it hasn't been heated to reflow temperature to activate it.   RA core solder specified by the manufacturer as non-corrosive is rarely a problem as all the core gets heated to reflow temperatures simply by using the solder but you need to be cautious with additional RA flux if you are hand soldering and not fully cleaning the board afterwards.

So-called No-clean fluxes can also cause problems if not fully heated to their activation temperature + are generally much harder to clean effectively.

Water washable fluxes are best avoided for hobby, prototyping and repair work, as few workshops have the equipment required to effectively wash their residue from under components and any trapped residue is a corrosion timebomb.

* US milspec (MIL-F-14256) R flux is broadly equivalent to IPC ROL0 flux and RMA to ROM0.  IPC ROL1 and ROM1 fluxes contain halides (or organo-halogen compounds that can react at soldering temperatures with metal oxides to form halides), which significantly increase the risk of corrosion if improperly washed or if unwashed in humid environments.
« Last Edit: October 13, 2021, 09:24:08 pm by Ian.M »
 
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Offline tooki

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Re: Looking to buy some flux (pen+paste)
« Reply #23 on: October 13, 2021, 12:04:05 pm »
I went with the RA SRA flux : https://www.amazon.ca/gp/product/B008ZIV85A/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

Because RA flux works better.
FWIW, there exist modern no-clean fluxes that are more effective than traditional RA fluxes. There's been a lot of progress over the years. (For example, Kester 275 and 245 no-clean flux cores significantly outperform the traditional Kester 44, according to their wetting specs.)

I see no reasons to buy two types of fluxes...the RA SRA puck would do..  I will use a toothpick to apply the flux...but I am wondering how to clean the RA flux residue ? My understanding is that I should apply IPA 99% and then use a swab to clean the board etc ? what if flux gets under the components and the swab cannot reach them ?
I recommend using a commercial flux remover. They're simply superior to IPA. (Even in fluxes that are fully removed in IPA, which many are not, IPA still takes longer to dissolve it and ends up needing more solvent.)

Getting it out from under components requires either an ultrasonic bath (with compatible flux cleaner) or patience and generous solvent application. If you have compressed air, you can use that to help cajole dissolved flux out. If you don't, you can shake the board off to help coax it out. You may have to do it a few times to get it all. After your final solvent rinse-and-shake, let it dry and see if you get residues. If there's a trail of residues from under a component, do more cleaning.
 

Offline tooki

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Re: Looking to buy some flux (pen+paste)
« Reply #24 on: October 13, 2021, 12:08:22 pm »
To be avoided are fluxes that either immediately cause current leakage or leave residues that  absorb moisture causing leakage problems later. A Chipquick branded flux that I tried, caused immediate leakage that remained after the PCB was cleaned. It gradually came good on its own. 

Extra: It actually is SMD291, there is possibly no problem when used to reflow SMD rather than for hand soldering.
I just saw the edit, made just after my original reply to you.

What'd you clean it with? If you used just IPA, it's possible that contaminants were left behind, since many (most?) no-clean fluxes aren't fully soluble in IPA. A more thorough cleaning with proper flux remover would make it fine.

As you alluded to, no-clean fluxes have to be fully heated to deactivate them, which isn't guaranteed with hand soldering. In the latter case, you have to do a thorough cleaning. If you cleaned and had leakage, then the cleaning was incomplete.
 


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