Soldering is a process that has been holding many industries together. From electronics to plumbing, no matter where you look, you will find a lead-free or tin-lead solder wire holding metallic components together.
Tin lead solder wire is more popular among hobbyists now. However, it has enjoyed its fair share of popularity in the commercial industry as well until lead-free solders replaced it for toxicity.
In this article, we are introducing the hobbyists-favorite, lead solder wire. We will begin by explaining what a tin-lead solder wire is and conclude this article with some of its most common benefits.
So, without further ado, let’s begin.
Tin Lead Solder Wire
If we say that the tin lead solder wire was here many years before technological break-through, we won’t be wrong. Lead has been in use for soldering since the times of the ancient Romans. When they used it for soldering plumbing pipes.
Solders are low-melting metals. They melt significantly lower than conventional metals and then solidify quickly thus creating a strong solid bind between the adjoining metals.
The tin lead solder wire is an alloy of two metals, namely tin, and lead. The most commonly used tin lead solders use a larger composition of tin and a lower composition of lead. These solders are more popular among hobbyists because they melt easily and are convenient to use.
It is not hard to imagine why lead-based solders melt easily. Tin is a low-melting metal while lead is very soft. And when we combine these to metals to form an alloy, they create a solder that melts easily, due to tin. And is soft, due to lead.
The tin lead solder wire ruled the world of soldering up until the end of the 20th centuries when some studies highlighted its toxicity. Since then, it has lost its popularity to lead-free solders, which are not harmful to humans and the environment.
Lead-based solders, however, have not lost all of their limelight and still enjoy being the favorite choice among hobbyist solderers.
These solder wires are available in different varieties with choices between diameters and composition. Most soldering wires are available in three common diameters including 0.02, 0.04, and 0.063 inches. As far as composition is concerned, we will discuss it in the next section.
The Composition of Tin Lead Solder Wire
All lead-based solders are available in two compositions. You can either get your hands on a 60/40 tin lead solder wire or you can buy a 63/37 tin lead solder wire. Both types of lead-based solders have their advantages and drawbacks. But in any case, they share their good wettability, ease of use, low melting, and of course, toxicity.
Sn63Pb37 Solder
The 63% Tin 37% lead solder is also known as Sn63Pb37 solder. Needless to say, it contains 63% tin and 37% lead. This solder is often the most preferred type of tin lead solder because it is a eutectic solder. We’ll get to eutectic and non-eutectic solders in a bit.
Moreover, melting at around 183 °C, this solder is the lowest-melting solder and hence, is super easy to use. And because it is a eutectic solder, it also enjoys the feature of forming stronger and more reliable solder joints.
The mechanical strength of a solder increases with the percentage-composition of tin. And since this solder contains a significant amount of tin, it also has the maximum tensile strength out of all the other compositions of tin-lead solders.
Sn60Pb40 Solder
The tin-lead alloy which contains 60% tin, and 40% lead is known as Sn60Pb40. Despite being a non-eutectic solder and being relatively difficult to use, it is the most common type of lead-based solder that is in use today.
Working with a 60/40 tin lead solder wire requires more vigilance because it is non-eutectic. It melts and solidifies over a range of temperatures. Hence, once melted, there comes a transition stage where the solder exists as a semi-solid. In this stage, if the joint moves even slightly, there stands a risk of the formation of a cold joint. A cold joint is a solder joint that looks fine from the outside, but it is weak from the inside and sits at risk of failing.
Apart from the main elements, tin, and lead, lead-based solders may also contain other elements in trace quantities. These trace elements include antimony, copper, nickel, and others.
The presence of antimony in the tin-lead alloy enhances the mechanical properties of the solder while maintaining its good wettability. While copper and nickel minimize the chances of the formation of tin whiskers.
Eutectic vs Non-Eutectic Tin Lead Solder Wire
We discussed in the previous section how the 63/37 tin lead solder is eutectic while the 60/40 solder is non-eutectic. Now, we will explain the difference between eutectic and non-eutectic.
If we talk about literal meanings, eutectic means something the melts easily. And then, non-eutectic would mean something that does not melt so easily.
Eutectic alloys, like 63/37 lead-based alloy, melt and solidify at a single temperature. While non-eutectic alloys, like 60/40 lead-based solders melt over a range of temperatures.
Hence, eutectic alloys melt and solidify quickly, thus they are easier to use because they do not present difficulty due to the semi-solid transitional state that the non-eutectic solders offer, as discussed above.
Benefits of Using Tin Lead Solder Wire
Despite being born more than two decades ago, lead-free solders have still not managed to eliminate lead-based solders from the soldering business. The reason why lead-based solders have held their ground and will continue to do so are the benefits that we’ll discuss below.
More Affordable
The biggest plus point that lead-based solders have is that they are more affordable than lead-free solders. Even though the 63/37 lead-solder is slightly expensive, but since these solders do not contain any expensive metals like silver, hence they are more economically priced.
Easy to Use
As we discussed above, tin lead solder wire melts easily and flows well. Therefore, it is much easier to use and hence is often recommended for beginner solderers who are learning soldering.
Lower Melting Temperature
Because the melting point of these solders is low, therefore they are often preferred while soldering electronic boards or temperature-sensitive elements. They do not require an increased amount of heat, which keeps the neighboring electronic components safe.
Moreover, because they melt quickly at a lower temperature, so, using a lead-based solder also reduces the soldering time.
Simple Equipment
If you have tried to transition to lead-free soldering from lead soldering, you would know that you cannot solder with lead-free alloys with a typical soldering iron.
However, this is not the case with lead-based solders. You can use a simple soldering iron and any available flux, and you will be able to create good solder joints.
Better Wettability
Another feature that has enabled lead-based solders to hold their ground is their ease of flow and better wettability.
Lead-based solders once melted flow and spread over the metal joint easily and then solidify quickly. Which is another reason why they are easier to work with and form better joints.
Conclusion
Tin lead solder wire has been in use for many decades and is not going anywhere anytime soon. These solders have two common compositions. They either contain 60% tin and 40% lead or they come with 63% tin and 37% lead.
The Sn63Pb37 is a eutectic solder, melts at the lowest temperature, and is easier to use. But it is also more expensive than Sn60Pb40 solder wire which is a non-eutectic solder and offers some difficulty in use due to its transitional, solid-liquid phase.
The tin lead solder wire offers numerous benefits including ease of use, affordability, and good wettability when compared to lead-free solders. But there is one disadvantage inherent to these solders. That is its toxicity. Which is becoming the reason for its demise.
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