Flux - so many types

I didn't know there were so many types of flux until recently, and there's probably more than what I listed below. What do you like for modding? Do I even want to know the benefit and drawbacks of all these types of flux and flux devices?

Solder paste (Amazon) -- not for electronics

No clean liquid flux pen (Amazon)

No clean flux paste syringe (Amazon)

Flux gel (Amazon)

High intensity flux paste (Fasttech)

High viscosity no clean flux paste (Fasttech)

Flux that works where rosin doesn't (Fasttech)

And would this bottle help?

There are three primary types. RMA, No Clean and Water Soluble.

Water Soluble flux MUST be completely washed off after being used. At home, it's HIGHLY unlikely you have the equipment/ability to do so.

No Clean and/or RMA should be used in 99% of modding projects. They both work in a similar way, but my preference between the two is RMA. Is doesn't have to be cleaned after use - but it can be, with Alcohol (isoProp or Ether).

Kester #186 is one of the best RMA Fluxes on the market.



Edit to add: Paste type Fluxes suck - but that's just my opinion. I use Liquid flux 100% of the time.

Edit to further add: The fluxes that will work on Stainless, Aluminum, etc - the usually "Non-Solderable" materials.. Are acid based. They are not safe for electronics. Do not use them.

Kester 186 ordered. What do you think about the needle syringes for applying it? I would think the squeeze bottle type is better than the plunger type. I have some plastic pipettes like that seller sells, but I think it'd flow too much.

These bottles are very similar to what I use. They work perfectly.


Thanks for the confirmation. I'll add that to my cart. Maybe I'll buy a few. The one review says the parts don't fit well, so I may seal the parts together with glue and use a new bottle every time.

Or I could get one from USPlastics. I've had good luck with their products.


If I can't wait, I can try recycling one of my inkjet refill kit bottles.

The flux pens work pretty well, too. I use both the pen and the bottle/needle.

I have no problems with paste at all.it goes where you put it and is real obvious how much and where it is .

I've never used fluid and I'm sure it works great too .

I'll just never use up what i have . Buy it once ,for all ,for life :P


Paste works great for me too. Had the same jar for ages. Apply it with a Q-tip. Although I rarely find it necessary when soldering small electrical components. But it doesn’t hurt either.

What's the real story with shelf life? I have stuff I use regularly that's way over the typical '2 month' life but haven't noticed any change at all in how it works. I kept my solder paste in the fridge for a while but that got annoying quick, I decided to just leave it out on the bench and see what happened... apparently nothing happened, so far.

What happens when it goes bad, what are the signs it's time to throw it out?

For such a short shelf life the must be there must be ingredients that can evaporate in it.

Can I just put out a special thank you to PilotPTK? I took the advice he posted on this thread and ordered the flux…

Let me just tell you this, I hadn’t ever really used flux before, and this stuff is absolutely amazing.


I love taking a wire that’s made up of smaller wires, liberally coating it in flux and then applying solder.

Glad it worked out well for you! There's a reason I suggest Kester 186 :)

Pilot, you’re the man!

Do you know if these pen type fluxes really contain the genuine Kester 186?



Yeah, they generally do contain the real stuff.. That said, I hate flux pens. Buy the liquid and a nice dispenser bottle and be happy.

Yeah, none of the bottled stuff can be shipped to Korea… :frowning:

Ah, yeah, I can see how that might be an issue. In that case, the flux pen is your next best option, and it does at least contain real 186.

A little late, but to add to this thread, get a nice alcohol pump bottle like one of these,
And either isopropyl alcohol or a can of denatured alcohol, and a few cheap bristle brushes to clean up with.

I use paste flux too, it’s great for when you need to stick down a component. Had the same tin for ages. It’s gotten quite a bit thicker of the years, but it still works, dab it on with a toothpick.

Why use poisonous alcohols when you can use Everclear pure grain alcohol? It has many other uses. Makes a dandy screwdriver, too. :party: