All About Solder: The Ultimate Guide

There are different types of solder available in the market. In this article, you will find all about them, their properties, and everything you need to know so that you can choose the right type of solder for your projects.

Let’s get started!

What is Solder?

Solder is a metal alloy with a relatively low melting point commonly used to attach metallic objects. The solder is melted using a heat source like a soldering iron and flows through the parts being soldered.
Solder solidifies once the heat source is removed, creating a strong bond between them.

It’s important to highlight that solder has a lower melting point than the parts to be joined to prevent damaging them.

What is Solder Used for?

Solder is used for attaching different components or parts to form an assembly or connection.

There are different types of solder depending on the field you are working with. For example, the solder used for electronics is not the same as the one used for plumbing.

I will make a list of the most common uses of solder.

Common Uses of Solder

1. Electronics
   In electronics, solder is used for attaching electronic components to PCBs (Printed Circuit Boards), connecting wires, assembling connectors, and repairing circuits, among other things. The solder used for these applications is an excellent electricity conductor, ensuring great electrical and mechanical connections.
2. Electric Work
   Like in electronics, solder is used by electricians to create strong mechanical and electrical connections. For high-power applications, thick wires, control boards, and other applications, it’s recommended to use a solder stronger and with a higher melting point than the one used in electronics.
3. Automotive Repair
   A thicker solder called “filler” is used as an alternative to putty for bodywork repairs. It’s an excellent way to repair minor dents and bumps, smoothening loose joints and rough surfaces.
4. Roof Repairs
   Solder is also used for building, repairing, and sealing metal roofs and flashings. A special alloy is used for this purpose, similar to the one used for plumbing, the next item on this list.
5. Plumbing
   Special solder is used in plumbing to join and repair copper and other metallic pipes. It’s also used to cover holes and join parts together.
6. Soldering Metal Gutters
   Metal gutters are made of similar materials as metallic roofs, and their parts are usually joined using solder, which creates a secure bond while sealing the seams and preventing leaks.
7. Working with Stained Glass and Mosaics
   Silver or tin-lead solder combined with flux is used over the copper foil or lead came used to join the pieces of these artworks.
8. Jewelry Making
   Solder is also used in some jewelry projects to create or repair metallic jewelry pieces. For example, a jeweler might use solder to repair a broken link in a gold bracelet.

What is Solder Made of?

Solder is made of different metal alloys and, in some cases, may contain materials like rosin, flux, or other non-metallic substances. Tin and lead are the two commonly used material for solders.

The composition of solder varies based on its intended use and application. For example, solder used in electronics and electrical jobs needs to be an excellent electrical conductor, a characteristic that is irrelevant for applications like plumbing.

When talking about solder, most people immediately think of tin and lead alloys. However, with the passing of time and the evolution of technology, there are currently more than one hundred varieties.

For simplicity and practicality, I will focus on the most commonly used alloys and materials you can find at hardware stores. As an interesting fact, only in the aerospace and heavy industries, there are at least fifty special alloys designed for specific uses and functions.

Composition of Solder

Solder’s materials and composition usually have more incidence in the final melting point and its applications.

Lead was one of the main materials used to manufacture solder because of its low fusion point; however, in the past years, the awareness about its toxicity and environmental impact caused the appearance of lead-free alloys. In some countries, lead solder became a forbidden substance; in others, it’s still available, but more and more people are moving to lead-free alternatives.

Depending on where you live, you can still find tin and lead solders and, in some cases, a third material is added to improve the alloy’s overall characteristics. For example, silver or copper is added to improve the alloy’s conductivity, ideal for electronics, and antimony for plumbing applications because it adds hardness and mechanical stress resistance to the solder.

According to the composition, we can group solders mainly into types.

1. Lead-based solder, and
2. Lead-free solder

Below, you will find a list of the most common types of lead and lead-free alloys and their uses:

Lead-based Solder

Tin-Lead: These alloys are represented by numbers in the format of 63/37. The first number indicates the percentage of tin, and the second is the percentage of lead in the alloy.

The most common ratios or proportions are:

• 63/37: This is one of the most common and widely used tin-lead alloys, frequently used in electronics.
• 60/40: This alloy is one of the most used for plumbing, stained glass work, and glass art.
• 50/50: This tin-lead alloy is frequently used in high-voltage electrical applications.
• 30/70: This alloy is used in applications with more heat; thus, a higher melting point is required. For example, high-output electric motors.
• 10/90: Nowadays, this alloy is hard to find because of its high lead level. It was practical for aviation electronics, industrial machinery, power electronics, heat exchangers, and other elements that worked in high-temperature environments.

Other popular lead-based solders are lead-copper alloys and trimetallic alloys, where a third element is added to obtain extra features.

• Lead-Copper: This alloy is ideal for plumbing and roofing because of its sealing and anti-oxidation properties. It’s perfect for long-lasting bonds and seals, and the hardest alloys have a melting point of 400°C (752°F), making it great for melting with different tools.

Trimetallic (Lead-based)

Examples of trimetallic alloys are:

• Tin-Lead-Silver: Silver adds extra strength and conductivity, making this alloy ideal for high-performance electronic applications.
• Tin-Lead-Bismuth: Bismuth lowers the melting point and improves the product’s wetting properties. It’s ideal for working with temperature-sensitive materials.
• Tin-Lead-Copper: Copper enhances the alloy’s strength and conductivity, making it suitable for applications where hardness and electrical performance are equally important.
• Lead-Tin-Antimony: This alloy is designed for roofing, plumbing, and joining metals requiring strong, durable bonds. The alloy’s melting point is between 250°C and 330°C (484 to 636 °F), which makes it perfect for working with conventional or butane soldering irons.

Lead-free Solder

• Tin-Silver: This alloy is an excellent replacement for the 63/37 tin-lead solder and is widely used in many industries, from electronics to plumbing.
• Tin-Copper: It’s one of the most popular lead-free alloys, with excellent thermal and electrical conductivity. It’s ideal for electronics and other applications.
• Tin-Bismuth: This is the lead-free alloy with the lowest melting point (only 95°C or 203°F). It’s ideal for working with delicate thermal sensitive parts.
• Tin-Zinc: This alloy offers great ductility and has a relatively low cost. It’s great for working with aluminum and galvanized steel. It’s not the best in terms of anti-corrosion and oxidation properties, but it does the job.
• Tin-Antimony: This solder creates hard connections and is widely used in industrial applications.
• Tin-Nickel: This solder is widely used in the aerospace industry because of its excellent mechanical properties and resistance to thermal cycling.

It’s important to consider that commercial lead-free solders have melting points from 5 to 20 °C higher than similar solders containing lead.

Types of Solder

There are different ways to classify solder.

1. Based on the composition
2. According to the alloy’s melting point, and
3. Based on the type of core

We have already discussed the different types of solder based on the alloy composition in detail in the previous section.
So, let’s see the other two types of solders.

Soft and Hard Solder

Solder alloys are split into two groups based on their melting points.

Soft solder has a relatively low melting point, which goes from 90 to 450°C (194 to 842°F), and solder with a melting point above 450°C or 842°F is considered as hard solder. Soft solder is ideal for electronics and working with delicate or heat-sensitive materials, as it enables soldering without subjecting components to potentially damaging high temperatures.

Hard Solder: On the other hand, high melting point solder (or hard solder), is used for applications such as plumbing or automotive repairs due to its ability to withstand high temperatures and mechanical stress. Besides, hard solder is more malleable and, thanks to its longer cooling time, allows molding it while it’s being applied.

According to the American Welding Society, soldering involves using soft solder with melting points below 450°C or 842°F. Processes that require more heat than this fall into other categories, such as brazing or welding.

Considering that the most powerful soldering irons can reach up to 480°C (896°F), it’s essential to know the solder’s melting point before starting a new project.

Core Style Classification

Solder can also be classified by its core or the lack of it.

• Rosin Core Solder
  This solder is one of the best for electric and electronic applications. It usually comes in the shape of a spool of wire; the center has natural rosin, which is a resin derived from pine trees.
  Rosin works as flux, a material used to clean and prepare the surfaces being soldered by removing oxidation and enhancing the solder’s wetting and bonding. Between the resin core and the outside layers, there is a thin air gap.
  The outer layer is usually made of tin and lead or lead-free alloys.
• Acid Core Solder
  This solder type also looks like a wire, but the core is filled with acid-based flux, which is stronger than rosin. This flux is more aggressive than regular flux, removing and preventing oxidation and ensuring a solid connection between the workpieces.
  Acid core solders are designed for sheet metal work, plumbing, and applications where a solid bond is crucial.
  This type of solder is not recommended for electronics because it’s corrosive and harmful to electronic components and circuits.
• Solid Core Solder
  As the name suggests, this type of solder doesn’t have a hollow core; it’s completely solid.
  It can be used in multiple applications, depending on the alloy used, its melting point, etc.

Forms of Solder

Solder comes in different shapes, depending on the application. It’s commonly sold in reels with a wire solder that comes in different thicknesses, being most common .05mm, .08mm, and 1mm.

Plumbers usually use much thicker solder, which is sold in bars.

Solder is also sold in thin sheets, ideal for jewelry making and other crafts.

Selecting the Right Solder

When choosing the solder for your project, it’s important to consider its intended use, melting point, electrical and mechanical resistance, and practicality.

For example, if you are working on an electronic project, it’s important to check how much heat the components you are working with can endure so that you can make sure to use solder that won’t lead you to overheat them. In the case of plumbing, roofing, and copper soldering, where mechanical strength is key, you should choose a solder with excellent mechanical properties but with a melting point that matches your tool’s heating capacity.

Electronics

As a rule of thumb, when working on electronics, choose a solder that provides reliable electric and mechanical connections with a melting point way below the components you are working with.

Construction (Plumbing, Roofing)

When working in plumbing and roofing, choose the hardest solder you can but within the limits of your tool’s heat output. If you have a proper torch, you won’t have a problem using any solder, and you can go for the hardest types.

Electrical Work

When working in electricity, make sure to choose a solder with good mechanical and heat resistance.

Environmental Impact and Safety

Another thing to consider is the environmental and health factor; try to avoid lead-based solder when working in plumbing applications where the lead will be exposed to running water that you or others may end up drinking or may contaminate other water sources.
Besides, lead-free solder is safer since its fumes are not as poisonous and dangerous as lead-based solder.

While lead-based solder is sometimes better in terms of conductivity and ease of use, try to avoid it as much as possible.

Safety Considerations

• Always wear safety goggles or protective eyewear to protect your eyes from potential solder splatters and/or debris and the fumes of melted solder.
• Wear safety gloves to protect your hands from burns and also to protect your skin from lead when working with lead-based solder.
• Always wash your hands carefully when finishing, mostly if you were in contact with lead-based solder.
• Keep flammable materials away from the soldering area to prevent fire hazards.
• Work in a well-ventilated area or use an air extractor to prevent inhaling potentially toxic solder fumes.
• Keep solder away from kids and pets to prevent accidental ingestion.
• Use a heat-resistant work surface or a soldering mat to protect your work area from damage and prevent fires.
• Keep a fire extinguisher nearby in case of fire.
• Use a soldering iron support or a heat-resistant stand to hold the soldering iron when not in use to prevent accidental burns or damage to surfaces.
• Never leave a heated soldering iron or butane torch unattended.
• Unplug the soldering iron when not used and let it cool down before storing it.
• Always handle the soldering iron with care and avoid touching the hot tip to prevent burns or injuries.
• Follow the manufacturer’s instructions and guidelines for your specific soldering iron model.
• Inspect the soldering iron cord for any sign of damage and replace or fix it if needed.

Common Problems and Solutions in Soldering

Below, you will find a list of the most common soldering problems and their solutions.

Solder Won’t Melt

This problem can be caused by several things.

First, make sure that you are using a soldering iron or heating source with enough heat to melt the solder. If you are using the right soldering iron, check the tip.
Oxidation and dirt act as insulators, preventing heat from reaching solder properly. If that’s the case, try to clean and re-tin your soldering iron’s tip and try again.

If that doesn’t work, check for damage on your soldering iron’s tip. It might need replacement.

If the tip is clean and in good shape and still doesn’t heat properly, check that it’s correctly plugged into the soldering iron’s heating element, mostly if you removed it recently for cleaning. Loose tips don’t make good contact with the heating element, becoming unable to heat solder properly.

If you are working with a high melting point or thick solder, pour some flux on the tip and try again. If none of this works, it may be time to get a new soldering iron.

Solder not sticking

The causes of solder not sticking can be the same as listed above, and besides, you should check some additional issues:

Ensure that the surfaces you are soldering are clean and rust-free. Dirt, corrosion, and impurities prevent solder from sticking properly. Also, check you are using the right type of solder for the intended application.

If none of this works, try using some flux to clean the parts and improve the solder’s efficiency.

Excessive Solder / Solder Bridges

Solder bridges can be formed due to excess solder on the soldering iron’s tip. This can be caused by an incorrect tinned tip, excessive solder, or using solder thicker than the component’s gap. Excessive temperature or humidity can also cause bridging issues; ensure not to overheat the parts or the PCB when soldering.

Another cause of solder bridges is using a thicker soldering iron tip than the gap between the components. Using a thinner tip may solve the problem.

A tip in bad shape can also cause solder bridges.

In other cases, mostly if you are building a project, it could also be a defect of the PCB, where the soldering pads are too close to each other. In that case, you can fix it using soldering masks, which are templates designed to prevent this problem.

Conclusion

There are countless types of solder and uses for it. However, if you get familiar with the parts or pieces you want to solder, finding the right solder for your application becomes much easier.

When it comes to electronic use, I always recommend 63/37 solder with rosin core; it provides excellent results and is easy to use and find.

For plumbing and roofing applications, I think choosing a lead-free solder is the best way to go, to care for your dear ones, other people, and the environment, besides avoiding contaminating water sources.

For applications like stained glass, you should use solder that matches the foil or lead came you are using; in both cases, remember to use flux to improve your joints.

Remember to follow the safety precaution listed in this and other of my soldering articles to prevent accidents and injuries, and remember that although it seems a simple task, it involves heat, fumes which usually are dangerous for your health, and in most cases, electricity, so solder responsibly.

Remember to keep your soldering iron clean for a pleasant and trouble-free soldering experience. Don’t rush; take your time and make sure to have everything ready before starting soldering and remember, like in any other jobs, when you solder, the more you rush, the slower it goes.