Soldering is one of the most fundamental skills needed to dabble in the world of electronics. The two go together like peas and carrots. And, although it is possible to learn about and build electronics without needing to pick up a soldering iron, you’ll soon discover that a whole new world is opened with this one simple skill. We here at SparkFun believe that soldering should be a skill in everyone’s arsenal. In a world of increasing technological surroundings, we believe it is important that people everywhere be able to not only understand the technologies they use everyday but also be able to build, alter, and fix them as well. Soldering is one of many skills that will empower you to do just that.
In this tutorial we will go over the basics of through-hole soldering – also known as plated through-hole soldering (PTH), discuss the tools needed, go over techniques for proper soldering, and show you where you can go from there. We will also discuss rework as it pertains to through-hole soldering and give you some tips and tricks that will make fixing any piece of electronics a breeze. This guide will be for beginners and experts alike. Whether you’ve never touched an iron before or are looking for a little refresher, this tutorial has a little something for everyone.
As stated earlier, you can learn about and build electronics without touching a soldering iron. If you would like to learn more about electronics theory before learning to solder, we recommend starting with some of these tutorials:
If you would like to know more about building circuits without needing to pick up a soldering iron, check out our solderless breadboard tutorial:
Lastly, we will be building upon some previous tutorials, so it is suggested that you read about and understand these subjects before moving forward in this tutorial:
If you’re all caught up on the above reading, let’s dive right in!
Before learning how to solder, it’s always wise to learn a little bit about solder, its history, and the terminology that will be used while discussing it.
Solder, as a word, can be used in two different ways. Solder, the noun, refers to the alloy (a substance composed of two or more metals) that typically comes as a long, thin wire in spools or tubes. Solder, the verb, means to join together two pieces of metal in what is called a solder joint. So, we solder with solder!
Solder wire sold as a spool (left) and in a tube (right). These come in both leaded and lead-free varieties.
One of the most important things to be aware of when it comes to solder is that, traditionally, solder was composed of mostly lead (Pb), tin (Sn), and a few other trace metals. This solder is known as leaded solder. As it has come to be known, lead is harmful to humans and can lead to lead poisoning when exposed to large amounts. Unfortunately, lead is also a very useful metal, and it was chosen as the go-to metal for soldering because of its low melting point and ability to create great solder joints.
With the adverse effects of leaded soldering known, some key individuals and countries decided it was best to not use leaded solder anymore. In 2006, the European Union adopted the Restriction of Hazardous Substances Directive (RoHS). This directive, stated simply, restricts the use of leaded solder (amongst other materials) in electronics and electrical equipment. With that, the use of lead-free solder became the norm in electronics manufacturing.
Lead-free solder is very similar to its leaded counterpart, except, as the name states, it contains no lead. Instead it is made up of mostly tin and other trace metals, such as silver and copper. This solder is usually marked with the RoHS symbol to let potential buyers know it conforms to the standard.
When it comes to manufacturing electronics, it’s best to use lead-free solder to ensure the safety of your products. However, when it comes to you and your electronics, the choice of solder is yours to make. Many people still prefer the use of leaded solder on account of its superb ability to act as a joining agent. Still, others prefer safety over functionality and opt for the lead-free. SparkFun sells both varieties to allow individuals to make that choice for themselves.
Lead-free solder is not without its downfalls. As mentioned, lead was chosen because it performs the best in a situation such as soldering. When you take away the lead, you also take away some of the properties of solder that make it ideal for what it was intended – joining two pieces of metal. One such property is the melting point. Tin has a higher melting point than lead resulting in more heat needed to achieve flow. And, although tin gets the job done, it sometimes needs a little help. Many lead-free solder variants have what’s called a flux core. For now, just know that flux is a chemical agent that aids in the flowing of lead-free solder. While it is possible to use lead-free solder without flux, it makes it much easier to achieve the same effects as with leaded solder. Also, because of the added cost in making lead-free solder, it can sometimes be more expensive than leaded solder.
Aside from choosing leaded or lead-free solder, there are a number of other factors to consider when picking out solder. First, there are tons of other solder compositions out there aside from lead and tin. Check out the Wikipedia solder page for an extensive list of the different types. Second, solder comes in a variety of gauges, or widths. When working with small components, it’s often better to use a very thin piece of solder – the larger then number, the smaller the gauge. For large components, thicker wire is recommended. Last, solder comes in other forms besides wire. When getting into surface-mount soldering, you’ll see that solder paste is the form of choice. However, since this is a through-hole soldering tutorial, solder paste will not be discussed in detail.
SparkFun offers many sizes of spools of solder in both leaded and lead-free varieties. Whether you just need enough for one project or are stocking up for the coming winter, SparkFun has what you need.
You can visit the Soldering category of the SparkFun catalog for more solder options as well.
Now that you know how to choose the best solder for the job, let’s move on to tools and more terminology.
There are many tools that aid in soldering, but none are more important than the soldering iron. If nothing else, you need at least an iron and some solder to accomplish the task at hand. Soldering irons come in a variety of from factors and range from simple to complex, but they all function roughly the same. Here, we’ll discuss the parts of an iron and the different types of irons.
Here are the basic parts that make up a soldering iron.
Several types of tips. From left to right, the bevel tip (aka hoof tip), two conical tips with varying widths, and the chisel tip.
Changing the tip is a simple process that consists of either unscrewing the wand or simply pushing in and pulling out the tip
Two varieties of wands. Notice how the tips screw into the wand allowing for interchangeability. Some wands have tips that simply push in and pull out without any attaching mechanism.
Some irons consist of just a wand that plugs into a wall outlet. These irons are as simple as they come, and they do not have any controls to vary the temperature. In these irons, the heating element is built directly into the wand.
A simple soldering iron that consists of just the wand. Some of these irons do not offer interchangeable tips.
Two variations of a soldering iron base. On the left, a digital base, complete with control buttons and a digital display. On the right, an analog base that uses a dial to control the temperature.
The base typically is comprised of a large transformer and several other control electronics that safely allow you to vary the heat of your tip.
The insides of a soldering iron base
Different types of iron cradles. Notice some allow for a regular sponge while others hold a brass sponge.
A brass sponge. If your iron stand doesn’t have a spot for a brass sponge, you can get one with its own base.
Whether you’re just beginning or a seasoned pro we’ve got a soldering iron for you!
Now that you know the ins and outs of a soldering iron, it’s time to discuss the other tools that will aid you on your soldering adventure.
These tools aren’t necessary, but they sure do make soldering easier at times.
Let’s put all these tools into action. This first video will go over the basics of soldering your first component – headers!
Check out the Vimeo version here.
It’s really that easy! Follow Dave’s simple rules to make every solder connection a good one.
We’ve also put together this digram to help you better understand what makes a good solder joint.
Click for a larger image.
When you are finished, tin the tip to increase its life before turning your soldering iron off.
Once you get the basics of creating good solder joints, it’s time to learn some of the more advanced PTH techniques that you can utilize. This video goes over using flux, removing solder jumpers, desoldering components, along with some other tips and tricks.
Here are some other tips for PTH soldering:
Desoldering can often be the best way to learn how to solder. There are many reasons to desolder a part: repair, upgrade, salvage, etc. Many of the techniques used in the video aid in the desoldering process.
There is another method of removing solder from through-holes that we refer to as the slap method.
If you’re ever unsure if the solder joint you created is making an electrical connection, you can use a multimeter to test for continuity.
Looking for more tips and tricks? Check out these advanced techniques to rework SMD components according to Pete.
When working with lead-free solder, flux tends to get everywhere, be it from the flux in the solder or from external flux applied by the user. Flux can corrode the PCB and components over time, thus it’s good to know how to clean your PCBs so they’re free of any flux residue. The simplest way to clean a board is to use a small brush (toothbrushes work great) and some isopropyl alcohol. If you are soldering more than a few boards, it may be necessary to clean them in batches. For this, we recommend a crock pot filled with distilled water. The distilled water keeps other impurities and contaminants away from your circuit.
It’s not 100% necessary to clean your board, however, it will increase the life of your circuit tremendously. For more information on PCB cleaning, click here.
We’ve only just begun to travel down the soldering rabbit hole. Once you have mastered PTH soldering, you can try your hand at these other skills and tutorials.
For more information about soldering castellated mounting holes to pads, check out our guide on soldering castellated holes.
And, of course, what’s a soldering tutorial without something to solder. SparkFun sells a variety of kits that are great for honing your soldering skills. There’s even a Learn to Solder series of kits that have all the tools necessary to get started.
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