Open and unopened 135 and Rubypaste

What’s the difference between general purpose paste fluxes?

Rosin flux paste No. 135. Rubyfluid Paste flux.

They’re both popular, and they’re both labeled as “general purpose”.

They both come in little, flat jars.  Both fluxes are in paste form, and they’re both used for soldering.  They’re both easy to find, you can buy them easily on Amazon, as well as an assortment of other specialty websites and DIY stores.  And they’re both excellent fluxes to have in your arsenal.

It’s easy to think that these two popular fluxes are interchangeable, but they’re not.  In fact, if you use these fluxes for the wrong application, you’ll get poor soldering results: either you’ll get a bad joint, or the flux residues will corrode your part.

So how do you know when to use the Rosin Paste Flux No. 135 and when to use the Rubyfluid Paste Flux?

If you could boil it down to one question, this is the key one:

Are you soldering a part for electronics or an electrical component?

If yes, you are soldering an electronic or electrical component, then use the Rosin Paste Flux No. 135.

“Why?”, you wonder?

The best way to explain this is by explaining why you should NOT use the Rubyfluid Paste Flux for electronics.  The Rubyfluid Paste Flux contains zinc chloride as the primary activator.  No doubt this zinc chloride makes the Rubyfluid Paste Flux very effective for soldering, but it’s the after-soldering that we’re worried about.  The zinc chloride, which is your friend during soldering, can become your enemy after soldering.   Halides, like zinc chloride like to attract moisture and eat metal. And they don’t just stay where you soldered. Zinc chloride flux residues have a way of going where you don’t want them.  Even if you do the best job you can cleaning off the Rubyfluid Paste Flux residues, there’s a good chance you’ll leave some zinc chloride residue behind, and these residues will cause the electronic or electrical component to corrode and FAIL down the road.

So, if you’re fixing the PCB on your X-Box One, Arduino, Raspberry Pi, cell phone, or soldering an electrical wire on the kids’ new drone, don’t use the Rubyfluid Paste Flux.  Instead, use the Rosin Paste Flux No. 135, because it’s active enough to get the job done, but without harmful post-solder residues.  The flux residues that are left behind after soldering with No. 135 are milder than zinc chloride flux residues. And unlike the more migrant Ruby Paste Flux residues, the leftovers from No. 135 are encased in a protective rosin residue – this should leave your electronic component safe for the duration.  And if you want to remove the residues from Rosin Paste Flux No. 135, then use a solvent like mineral spirits, white spirits, electronics grade isopropyl alcohol (aka rubbing alcohol), or some other sort of electronics-friendly alcohol.

What about Rubypaste?

Now you’re left thinking, “then when should you use the Rubyfluid Paste Flux?” aren’t you? Well friend, don’t worry. It’s simple.  Anytime you need to solder copper, brass or even certain steel alloys in something that is non-electronic or non-electrical, then pull out the tried-and-true Rubyfluid Paste Flux.  It’s strong enough to get the job done, and unlike Rosin Paste Flux, Rubyfluid Paste will succeed in difficult-to-solder situations (such as badly oxidized copper).  In addition, the trademark ruby red color makes it easy to see where you’ve applied the flux.

  • Need to fix a copper pipe? Ruby’s your flux.
  • Soldering copper on a roof? Ruby’s is the “go to” flux for professional roofers.
  • Working on stained glass? Ruby’s been artisans’ favorite brand for decades.

Just remember – wipe off the Rubyfluid Paste Flux residues after soldering with a wet rag so that the flux residues won’t cause corrosion or discoloration.  (And if you’re using RubyFluid Liquid Flux, then you can wash off the flux residues with actual water.)

Need something stronger?

Keep in mind Ruby Paste Flux does have its limitations.  If you need to solder galvanized steel or stainless steel, then it won’t be strong enough.  With difficult-to-solder metals like galvanized steel or stainless steel, turn to Rubyfluid Stainless Steel Flux or Superior No. 71.

In summary –

Soldering electronic /electrical components? Rosin Paste Flux No. 135 (SDS/Spec sheet)

Soldering  NON-electronic/electrical components? Rubyfluid Paste Flux (SDS/Spec sheet)

And don’t forget to Contact Us with your flux questions.