Solder comes in a few different forms. Wire, sheet, and pallions (pre-cut squares) are the ones everyone knows about, and paste is 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 micro fine spherical solder powder, flux, and binder. It comes in copper, silver, and gold. That means that the material in the tube is real metal solder, and it’s premixed with flux. 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.
Advantages of Using Solder Paste
Solder paste is 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. 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 firescale or oxidation.
As per 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. After you’ve applied adequate solder, there may still be a little bit of paste coming out of the needle. If you’re doing multiple solder seams, you can save this for your next seam, or you can wipe it off into your scrap silver pile.
Applying Solder Paste
After 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 ball 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. If you see a spot where the solder didn’t flow, you can carefully touch it up by adding a bit more solder paste and re-heating it. 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. 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 is 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, so it won’t 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
|Easy||65% silver||Flow point 1325 ºF (718 ºC)||Melt point 1240 ºF (671 ºC)|
|Medium||70% silver||Flow Point 1360 ºF (738 ºC)||Melt point 1275 ºF (690 ºC)|
|Hard||75% silver||Flow Point 1450 ºF (788 ºC)||Melt point 1365 ºF (740 ºC)|
|Copper||Flow Point 1325 ºF (718 ºC)||Melt point 1240 ºF (671 ºC)|
Caring for Your Solder Paste
When you’re done soldering for the day, make sure to cover the tip of the solder paste needle (electrical tape works quite well). Otherwise, it will dry out. You don’t have to unscrew the needle every time you’re finished, if you’re going to be using it again soon. It’s a good idea to unscrew the needle and put the white plastic cap back in if you’re not going to be using it for a long time, or moving your studio. When you unscrew the needle, make sure to clean it out with a piece of scrap wire, and put it some place you won’t lose it. If you have various tubes of solder paste, make sure they are all marked with the appropriate melting temperatures and metals, so you don’t confuse them. If one of your needles becomes clogged, soak it in warm water for a few minutes, and then clean it out with a piece of scrap wire.