Soldering Paste

Solder comes in a few different forms. Wire, sheet, and pallions (pre-cut squares) are the ones everyone knows about. However, paste seems to be the one everyone has questions about. In this post I’ll clarify what solder paste is, what the advantages are, and how to use it.

What Is Solder Paste?

Solder paste is a homogeneous blend of very fine spherical solder powder, flux, and binder. It comes in different formulas for different metals such as silver and copper or even 14 or 18 karat gold. The solder in the tube is real metal solder, same as you would find in a sheet or wire. Like other solder, paste solder comes in different melting temperatures: easy (or soft), medium, and hard. Basically, paste solder is like any other kind of solder, it just comes in a different form, and has flux already included.

Advantages of Using Solder Paste

Solder paste is often considered the best form of solder to use when soldering tiny elements like jump rings, filigree, or earring posts. It is not so good for soldering larger elements, or for tasks that require a lot of solder or heat. One of the greatest things about solder paste is that it stays put, and won’t blow away as soon as you turn on your torch like tiny pallions or bits of wire might. Another advantage is the built-in flux. It can sometimes be necessary to use additional flux, but a lot of the time, solder paste just simplifies the process by not requiring the application of flux because it’s included in the paste. Next time you need to solder something tiny and need just a tiny amount of solder, reach for your solder paste, instead of getting frustrated with your shears.

How to Use Solder Paste

Using solder paste is similar to using any other kind of solder, but it is advantageous for getting into small spaces. To use it, first unscrew the white plastic cap, and screw in the needle tip. Don’t throw away the white plastic cap, as you may need it later. Seattle Finding’s solder paste comes with 2 different size needle tips so you can choose the one that works best for each application. Make sure the metal you’re about to solder is clean and free of oil, grease, polishing compound and excessive oxides. You may want to pickle it or rub it with steel wool if it isn’t clean. As with any kind of soldering, the cleaner the metal, the better the solder will flow. Before you apply solder paste, you might want to apply flux to the surrounding areas. Solder paste does have flux mixed in, but it is only there to help the solder flow, not to protect your metal from fire scale or oxidation.

As usual, make sure the pieces of metal you’re soldering together are flush together before you start soldering. To apply the solder paste, hold the needle where you want to deposit the solder, and press the plunger down firmly. This may take two hands at first, because you’re forcing a lot of material through a tiny opening. Apply more solder paste than you think you will need because it’s not 100% solder – the flux is mixed in as well. For example, if you’re soldering a bezel to a sheet, squeeze a line of solder all the way around where the bezel touches the sheet, even though if you were using sheet solder you’d only use a few little pieces. Another example: if you’re soldering an earring post to something, apply solder paste to both the end of the post and the area you’re attaching it to. Over time, you’ll get a better idea of how much you’ll need so you don’t over or under apply your solder – just like you had to when you first learned to solder with sheet.

Application of Solder Paste

To flow the solder, heat your project like usual, making small circles around the entire piece with a small or medium size flame on your torch. Soldering with paste solder is not recommended for larger pieces, so you should definitely be able to heat the entire piece equally with a small or medium flame. Your flux should bubble and melt, and your metal should start to glisten. When you’re almost to the melting temperature of your solder, it will bead up into teeny tiny balls. Don’t worry if they’re not all where you want them, and don’t try to move them around with your soldering pick. At this point, focus your flame on where you want to flow the solder and move it quickly back and forth. Wait for all of your solder to flow, meaning there should be no little balls left. Then turn off your torch. When you’re satisfied with your solder seam, quench it and pickle it until all the flux is gone. If you see little bumps of solder that didn’t flow where they were supposed to, sand them off with emery paper or an abrasive silicone wheel, and finish you piece as usual.

Different Melting Temperatures

If you have multiple solder seams close together on the same piece, you will probably want to use different melting temperatures of solder. Start with hard solder for your first task, and then move onto medium, and then easy, just as you would with sheet or wire solder. This way, you won’t disrupt your previous solder seams when re-heating the piece because it won’t need to get as hot for the solder to flow. If you only have one soldering seam on a piece, you can choose which solder to use. Most of the time this does not matter, but sometimes it does. If you’re soldering something that will have a lot of stress on it, like an earring post, use hard solder, as hard solder is stronger and less likely to break off under pressure. If you’re soldering something that has delicate stones in it, use easy solder, so there is less chance of damaging the stones.

Flow and melt points of silver solder paste