Solder Paste Flux?

Hi, Ron. Could you provide the GC part number?

Chris

Hi Chris,

I can only find GC 10-202 on the container. More accurately, it says "Water Removable Soldering Paste" with "Solder Flux" written on top.

The directions state:

1). Apply Water Removable Soldering Paste 2). Heat 3). Then add GC's pure non-leaded solder

So, I'm guessing this is just a flux? But if that's the case, why do I need to heat the paste first?

Thanks!

Hi, Ron. GC 10-0202 is a water cleanable, organic flux made to be used with a lead-free solder. I'm not sure if GC Waldom still sells that kind of solder. You can still use it with leaded solder, as long as it either has no flux core, or has an organic (water soluble) flux core.

Look on page 16 of the Chemicals section.

Flux is a good thing to have on the bench, because many times the circuit board pad has become somewhat oxidized, or the component isn't easily wettable for some reason. Also, extra flux usually means you don't have to heat as long to get a good solder joint. The small amount of flux in the solder wire core may not be enough to clean the surface of the pad.

To use the flux manually, apply it to the circuit board or area to be wetted. Apply the soldering iron to the area for a brief time to heat up the flux (it becomes reactive at higher temperatures, and is relatively inert at room temperature). You usually see it bubble, or a small amount of smoke will come of the flux as it's heated. Then apply the solder to the jointand release both the solder and iron as the joint is formed. The flux cleans and chemically activates the metal surface, making it more easily wettable by the solder. Otherwise, you might just have a blob of solder sitting over a dirty pad or component wire, with either poor or no electrical connection.

The advantage (such as it is) of organic water-soluble fluxes is, of course, that the residue can be cleaned after soldering without using banned solvents. This is something of an advantage, but organic fluxes are less inert than rosin at room temperature, and can cause conductive paths across the circuit board. Also, they can be kind of aggressive at elevated temperatures, causing etching of traces under SMT components that get hot. So, with organic water-soluble fluxes, you really should make sure to clean the boards in water after you're done (I like to use Palmolive Green in warm dishwater concentrations with a brush, followed by a straight hot water rinse and warming oven dry).

Also, this is a water-soluble organic flux, so you should avoid mixing it with rosin-based fluxes. Neither one works as well when they're mixed, and you usually end up with something that doesn't work or clean very well. Most wire solder has a flux core, so you should check before you use it. If you want extra flux with a rosin core, use GC-10-4202 liquid solder flux.

I hope this is the explanation you were looking for. If not, please post again.

Chris

Hi Chris,

Thank you very much for the informative post!

I have a Radio Shock solder that says "Silver-bearing solder." I don't see any indication of rosin-based flux. Will this work with the GC paste?

Also, to clean the board with water, do I need to use distilled water and not tap water?

Thanks!

Again, a part number would have helped. The website shows two current selections for "silver bearing solder". 64-035 shows rosin core on the webpage. The other, 64-013, doesn't show anything. It may or may not have a flux core.

If the label on the package doesn't say anything, you might want to take a razor blade or sharp utility knife and make a non-perpendicular cut in the wire. If you see something that looks like a hollow core in the center of the wire, it has a flux core. You then should determine whether it's rosin or organic. Failing everything else, if you happen to know what standard rosin flux smells like, just touch the tip of your hot iron with the solder and take a sniff.

However, it really should say on the package.

I would doubt Radio Shack would sell solder with organic flux (it's quite a bit more hazardous than the rosin stuff, and they do have lawyers), so if it does have a flux core, you probably shouldn't use it with your organic flux.

And if you're near the Radio Shack, you may want to look at Catalog #:

64-022. It's a 2 oz. Non-Spill Rosin Soldering Paste Flux, if you have to have some. But as I said, most solder comes with some kind of flux core, and that's sufficient for most electronics work.

By the way, if you are going to be using the Palmolive cleaning method (recommended by Bob Pease of National Semiconductor, along with the dishwasher method), plain very warm tap water should be adequate for most stuff. Use lots of it to rinse off any residue. Another pass with the brush while rinsing isn't a bad idea, either. Make sure, though, that everything on the board can be water-cleaned. Many things, such as pots, relays, switches, &c., will retain the water, and then cause you grief when you turn it on. Either that, or washing will remove lubrication, or cause oxidation. If you have these components on board, you have to install them after water washing.

Good luck Chris

Hi Chris,

Thank you again!

I found this page:

In it, the author mentions that "the solder is 0.015 inch silver-bearing solder made by Radio Shack (64-035E). In general, silver solder is becoming more common because there is a drive underway to remove/reduce lead from all products. While silver-bearing solder may have slightly improved conductivity, and it is much stronger than pure tin-lead solder, it does have a slightly higher flow temperature. Note: this solder, and as best as I can tell, all solder of that thin diameter, do not have a rosin core. The solder is simply too small to support a core of flux."

I have the same Radio Shack solder. However, when I search on the website I only found the one that you mentioned 64-035...and not

64-035E. I wonder if they are the same. The picture on the RS website does have the same marking except for the extra E on the part number.

Hi, Ron. I'm not familiar with Radio Shack solder. I've got a few spools of Kester (a 1 pound spool will last forever), and use those.

The 64-035 is eutectic 62%-tin, 36%-lead, 2%-silver solder, not the lead-free type. The silver is useful in SMT soldering to help prevent leaching from the component terminations, a big problem with hobbyist work. The 64-035 is also .015", and _does_ have a rosin flux core. Again, use a new razor blade to make a diagonal cut in the solder wire, and you should see it kind of fold in. Or just touch it to a hot soldering iron. If there's no flux, you won't see any wisps of smoke, hear any hissing when it melts, or get any smell off the solder. All flux is chemically active when it heats up, which means that it will give you an odor. I would think RS would give a different part number if they made a major change to a solid wire solder.

For manual SMT work, it's better to use some kind of extra flux, if only to help avoid overheating of components. If that's what you've got, you might as well try it. But you should get a feel for using the different types of flux, and choose one or the other if you're going to be doing this regularly. I'll use Kester "44" whenever I can for prototype and repair work, but if you need to clean the board, common sense as well as consideration for the environment might lead you to use the water-soluble organics.

Good luck Chris