Choosing Solder

If you bought a kit that came with solder, use it! But if not or for future reference, here are some basic considerations.

Lead vs. Lead-Free:

Leaded solder is MUCH easier to work with than lead-free. An entire article could be written about this topic, but it can be summarized with: lead-free solder has the potential to cause you far more headaches with very few benefits.

I strongly recommend using leaded solder until you have learned the fundamentals and feel confident in your soldering ability. Your chances of success with lead-free solder, as a beginner, are greatly diminished. Even after you’re highly proficient at soldering you should probably continue using leaded solder. The failure rate of lead-free solder joints over time is much higher, and it is simply less reliable.

Lead-free solder is widely use for commercial products due to environmental concerns. Countless tons of consumer electronics eventually pollute the Earth, so lead-free solder can help reduce contamination. Switch to lead-free solder when your projects are being manufactured and assembled by professional PCB fabricators.

When To Use Lead-free?

Lead-free solder is great when you are mass producing consumer electronics. Most products are not recycled, so reducing the amount of lead contamination into our planet is a worthwhile effort. The amount of lead in DIY electronics, however, isn't even measurable by comparison.

Switch to lead-free solder if your hobby turns commercial, and you are having professional PCB assembly companies fabricate and assemble your boards.

Leaded Solder Safety:

People often think the fumes that rise while soldering have lead in them, but they do not. The fumes are from flux, and they are equally (if not more) harmful in lead-free solder. We'll touch on this soon, but for now the biggest safety consideration when working with leaded solder is to WASH YOUR HANDS to remove any traces of lead when you are finished. Refrain from touching your face, eating, or touching other people until you wash your hands.

If you are soldering on a sensitive surface like a kitchen table, lay down newspapers to protect it from tiny bits of solder that will splash and clean the surface well when you are done.

Tin/Lead Ratio:

Leaded solder is made from a mixture of tin and lead, and is available in a variety of ratios.

60/40 or 63/37 are the most popular for DIY electronics, and the difference between them is negligible. Choose whichever is cheaper or more readily available.

Width of Solder Wire

0.031 or 0.032" (~ 0.8mm) is a good multi-purpose size.

Smaller can be used as well, but you'll have to push far more solder wire into each joint. I keep a roll of 0.6mm for SMD work, but probably wouldn't use anything narrower than this.

I don't recommend using anything larger than 0.032", though, since it will be too easy to add too much solder to joints.

Flux

Flux is a chemical substance that prepares the metal surfaces to bond with the solder. It is critical for soldering because it removes and prevents layers of oxidation on your component and PCB pad so the solder can properly bond to the metal.

Without it you would have unreliable solder joints.

Flux Core Solder (required)

Solder used for electronics like DIY pedals should always have a flux core. Most solder you find for electronics is suitable. Avoid plumbing solder, though.

For the majority of soldering, the flux inside your solder wire will be sufficient.

Understand, though, that once you melt the solder the flux burns off. If you are reworking a joint is often a good idea to add fresh solder in order to get more flux.

Additional Flux (optional)

In some circumstances it helps to have additional flux you can apply to the parts you are working on. For example, if you are working on surface mount devices (SMD), which are typically very small, it is often useful to apply solder directly from the tip of the iron. When the solder melts and adheres to the tip, though, the flux is burned off. Because of this you will need to first add additional flux to the work pieces.

Additional flux can come in a variety of formats:

• Gel in a syringe: my favorite. It’s easy to apply, sticks to the intended surface, and is tacky and can hold surface mount parts in place
• Liquid in a pen or bottle
• Paste

Flux Types

Rosin:

An aggressive flux that will work well for most situations, including older, moderately oxidized or corroded parts. However it leaves a thick, dark residue that must be cleaned with isopropyl alcohol (rubbing alcohol). Stronger mixes, e.g., 91%, make the job easier

No clean:

This is the least aggressive, and leaves less residue on the circuit board so it's often not cleaned off. This is my preferred type. If you'd like to clean it, use isopropyl alcohol just like with rosin

Water soluble [not recommended]

As the name implies it is cleaned with water, so care must be taken when using water-sensitive components. This is also a very aggressive flux. Because of various problems water causes (e.g., from minerals and oxide), I don't recommend using this flux.