I bought a "Solder Paste". It is in quote because I'm not really sure if it's a Solder Paste itself.

I researched about what Solder Paste is and, by definition, is defined as a mixture of small solder spheres with flux. It's also grey-like in color since it has tiny solder spheres.

So, it can be directly applied to the pads of the PCB and perform reflow soldering afterwards.

But here is the actual product I bought:

enter image description here

As you can see, it's brown-ish in color and I don't think there are tiny solder spheres in there.

And the direction in using this is to put ample amount on the pads then apply solder with iron or torchenter image description here

So my question is, is this really a solder paste or just flux? How can I use this, then?

  • 1
    \$\begingroup\$ Looks like flux for copper tube work to me... \$\endgroup\$ – PlasmaHH Jun 9 '17 at 8:22
  • \$\begingroup\$ it's a different kind of solder paste than you describe, or what's commonly used these days in vernacular EE english. that stuff is pretty useful, but not for SMD work... \$\endgroup\$ – dandavis Jun 9 '17 at 8:24
  • \$\begingroup\$ Why not for SMD soldering? \$\endgroup\$ – J. A. De la Peña Jun 9 '17 at 8:29
  • \$\begingroup\$ Because it doesn't contain any solder. \$\endgroup\$ – Leon Heller Jun 9 '17 at 8:48
  • \$\begingroup\$ @LeonHeller yes but do you think it will work if I use soldering rod and lead? thanks \$\endgroup\$ – J. A. De la Peña Jun 9 '17 at 8:57

This is not the stuff to use to solder electronic boards, this is for plumbing fittings, a flux to be used in addition to stick of solder.

Electronic boards require either 'flux-cored solder' for hand use, or 'solder paste', which is a mixture of small solder balls in a suitable flux, for machine use.

This flux is likely to be too aggressive to leave on a board, and will require cleaning, otherwise it's likely to damage the board. The flux used in flux-cored solder or solder paste is designed to be compatible with the materials on a PCB, and it's usually safe to leave the residues there indefinitely.

  • 1
    \$\begingroup\$ @dandavis The picture of the lid wasn't there in the beginning. From appearance alone, this answet was correct. The picture of the lid gives information that just wasn't there when this answer was posted. \$\endgroup\$ – JRE Jun 9 '17 at 9:27
  • \$\begingroup\$ fair nuff, sorry to bug you. you might update though. i think it's for commercial electrical work, not electronics. \$\endgroup\$ – dandavis Jun 9 '17 at 9:29
  • \$\begingroup\$ I think 'Eagle Electric' is the name of the company, and not a recommendation for how to use it. \$\endgroup\$ – Neil_UK Jun 9 '17 at 9:39
  • \$\begingroup\$ Checked at Eagle. They really do mean flux for electronics. \$\endgroup\$ – JRE Jun 9 '17 at 10:55

This seems to be an Asian-English thing- calling flux "soldering paste" or even "solder paste". Sometimes the word "cream" is in there.

I've seen it in China, Hong Kong and Taiwan, and this "soldering paste" is from the Philippines.

Here is some Asian-origin (real) solder paste:

enter image description here

As you can see, the alloy (Tin 63%/Lead 37%) is specified as well as the ball size 25-45um diameter. Most lead-free alloys are mostly tin, with a bit of copper and possibly other metals mixed in. There is a tin-bismuth alloy for the big spenders. It looks like a grey paste and under the microscope you can easily see that it is composed of tiny balls in a matrix of flux.

What you have is flux of some unknown type (although it's specified as non-corrosive so at least it (probably) isn't the typical highly acidic plumber's flux). You can stick multimeter probes into it and see if it is conductive.

Typical classes of fluxes are RMA (Rosin mildly activated), "no-clean" and water soluble. They have different characteristics, though for non critical circuits it may not matter which is used.

Here is a typical flux (RMA) from the same manufacturer:

enter image description here

As you can see, it's a translucent gel-like material with a yellowish tint, not dissimilar to what you have (however given the reference on the can to 'torch' I would be reluctant to try yours on circuits - it may be similar but have impurities that would be electrically conductive, for example).

Solder paste photo (from Adafruit):

enter image description here

Edit: From the comment/link by @JRE, the flux you have is claimed to be suitable for electronics:

enter image description here

"Noisy set" indeed. If you use acid flux at mains voltage (as a hapless customer of mine once did) the "set" will be noisy from all the electrical arcing.


It's called soldering paste, not solder paste. Solder paste has a grey color due to the contained solder.


This is flux, not solder paste.

and concerning how to use it, you gave us the instructions, just put some where you will be soldering (or just dip your iron in the stuff) and apply the good ol' solder & iron technique.

I doubt it would be useable in reflow soldering though.

  • \$\begingroup\$ Ok but will this work if I perform this? youtube.com/watch?v=lhOKSqipwqg \$\endgroup\$ – J. A. De la Peña Jun 9 '17 at 8:30
  • \$\begingroup\$ I think it will, yes, but i am not experienced enough with reflow soldering to be sure. \$\endgroup\$ – Sclrx Jun 9 '17 at 8:36

It's most likely flux. I say that because it is brown (as opposed to the grey that solder paste would be due to the tin content) and the suggestion of a torch, which is normally used for things like soldering pipes, not electronics.

Since electronic solder paste contains solder, it should specify whether it is lead-free or 60/40, 63/37, etc. This one doesn't say.


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