Selecting the right solder melting point is crucial for the success of your project. Soldering involves using a fusible metal alloy to join two or more metal parts together. The melting point of solder—the temperature at which it turns from solid to liquid—varies based on the alloy composition. Here’s a guide to help you make the best choice for your needs.
Understanding Solder
First, let’s get a handle on what solder is. Solder is a fusible metal alloy used to join together metal parts. The melting point of solder is the temperature at which it transforms from a solid to a liquid. This temperature varies depending on the composition of the solder alloy.
Most commonly, solder is made from a combination of metals like tin, lead, silver, and copper. Each metal has a different melting point, and by mixing them in different ratios, manufacturers create solder with specific melting points suited for various applications.
What is the Melting Point of Solder?
Solder melting points typically range from 90 to 450°C (190 to 840°F; 360 to 720 K), depending on the alloy. This wide range reflects the diverse applications and requirements for soldering in various industries.
- Common Alloys: The most frequently used solder alloys melt between 180 and 190°C (360 and 370°F; 450 and 460 K). These include popular types like tin-lead and certain lead-free solders.
Common Types of Solder and Their Melting Points
The melting point of solder can vary significantly depending on its composition.
Lead-Based Solder Melting Points
Lead-based solders, usually a mix of tin and lead (commonly 60/40 or 63/37 ratios), have been the industry standard for many years. The 63/37 solder melts at 183°C (361°F), making it a popular choice for electronics due to its relatively low melting point and excellent flow characteristics. However, due to health and environmental concerns, its use has declined in favor of lead-free alternatives.
| older Type | Composition | Melting Point (°C) | Melting Point (°F) |
|---|---|---|---|
| 60/40 Tin-Lead Solder | 60% Tin, 40% Lead | 183-190 | 361-374 |
| 63/37 Tin-Lead Solder | 63% Tin, 37% Lead | 183 | 361 |
| SAC305 Lead-Free Solder | 96.5% Tin, 3% Silver, 0.5% Copper | 217-221 | 423-430 |
| Tin-Silver Lead-Free Solder | 96.5% Tin, 3.5% Silver | 221 | 430 |
| Tin-Copper Lead-Free Solder | 99.3% Tin, 0.7% Copper | 227 | 441 |
| Bismuth-Based Low-Temp Solder | 58% Bismuth, 42% Tin | 138 | 280 |
| High-Temp Solder (Silver) | 93.5% Lead, 5% Tin, 1.5% Silver | 296 | 565 |
| Silver-Bearing Solder | 62% Tin, 36% Lead, 2% Silver | 179-190 | 354-374 |
| Tin-Lead-Antimony Solder | 62% Tin, 36% Lead, 2% Antimony | 178-190 | 352-374 |
| Nickel-Based High-Temp Solder | Nickel-based alloy | 450+ | 842+ |
Lead-Free Solder Melting Points
In response to the restrictions on lead-based solder, lead-free alternatives have become popular. These typically contain tin mixed with small amounts of silver, copper, or bismuth. Lead-free solders generally have higher melting points, often ranging from 217°C to 227°C (423°F to 441°F).
Here’s a breakdown of various lead-free solder compositions and their melting temperatures:
| Solder Alloy Composition (% weight) | Composition Detail | Melting Temperature (°C) | Melting Temperature (°F) |
|---|---|---|---|
| 97% In/3% Ag | Indium-Silver | 143°C | 289°F |
| 95.5% Sn/3.9% Ag/0.6% Cu | Tin-Silver-Copper | 217°C | 423°F |
| 95% Sn/5% Sb | Tin-Antimony | 232°C – 240°C | 450°F – 464°F |
| 95% Sn/5% Ag | Tin-Silver | 221°C – 240°C | 430°F – 464°F |
| 95.6% Sn/3.5% Ag/0.9% Cu | Tin-Silver-Copper | 217°C | 423°F |
| 65% Sn/25% Ag/10% Sb | Tin-Silver-Antimony | 233°C | 451°F |
| 91% Sn/9% Zn | Tin-Zinc | 199°C | 390°F |
| 95% Zn/5% Al | Zinc-Aluminum | 382°C | 720°F |
| 58% Bi/42% Sn | Bismuth-Tin | 138°C | 280°F |
| 97% Sn/2% Cu/0.8% Sb/0.2% Ag | Tin-Copper-Silver | 226°C – 228°C | 439°F – 442°F |
| 95.5% Sn/3.5% Ag/1% Zn | Tin-Silver-Zinc | 218°C – 221°C | 424°F – 430°F |
| 96% Sn/4% Ag | Tin-Silver | 221°C – 225°C | 430°F – 437°F |
| 91.5% Sn/8.5% Sb | Tin-Antimony | 232°C – 240°C | 450°F – 464°F |
| 97.5% Sn/2.5% Ag | Tin-Silver | 221°C – 226°C | 430°F – 439°F |
| 97% Sn/3% Cu | Tin-Copper | 227°C – 300°C | 441°F – 572°F |
Application-Based Selection
- High-Temperature Processes: Consider using solders with higher melting points such as 95% Sn/5% Sb (232°C – 240°C / 450°F – 464°F) or 95% Zn/5% Al (382°C / 720°F) to withstand multiple thermal cycles without reflowing the initial solder.
- Low-Temperature Processes: For thermally sensitive components, use solders with lower melting points like 97% In/3% Ag (143°C / 289°F) or 58% Bi/42% Sn (138°C / 280°F) to avoid damage.
Silver Solder Melting Points
Silver solder, also known as hard solder, contains a higher percentage of silver and is used in high-strength applications, such as jewelry making or plumbing. It has a much higher melting point, often exceeding 600°C (1112°F). This type of solder requires more heat but provides very strong joints, ideal for applications where durability is critical. (If you want to learn more about the melting point of silver, please click here)
Copper Solder Melting Points
With a melting point of about 1083°C (1981°F), copper solder is used for high-temperature applications. It’s less common for general soldering tasks but essential in specific industries like HVAC. (If you want to learn more about the melting point of copper, please click here)
Why Opt for Gold Alloy Solder Instead of Lead Alloy Solder?
Gold alloy solders, like Au80Sn20, are often chosen over lead-based solders due to their superior high-temperature performance. Lead-based solders, with a melting point of 327°C, lose strength above 245°C, which can be problematic during high-temperature processes. In contrast, Au80Sn20, with a melting point of 280°C, maintains its strength better under similar conditions.
This makes gold alloy solders ideal for applications involving final assembly processes, such as reflow or wave soldering, which occur around 250-260°C. They ensure reliable and durable joints, even in the face of potential overheating, unlike lead-based solders which may become too soft.
Why Choose a Eutectic Alloy Over a Non-Eutectic Alloy?
Eutectic alloys melt and solidify at a single temperature, allowing for faster, more efficient soldering and simpler fixturing. This leads to optimal joint quality and cost savings. Non-eutectic alloys, however, go through a solid-liquid phase during cooling, increasing the risk of hot-cracking and requiring more complex process adjustments. Therefore, eutectic alloys are preferred for their speed and reliability in soldering.
Which Solder Should Be Used?
The selection of a solder alloy hinges on two primary criteria: the solder melting point and any subsequent thermal processes. For processes involving multiple thermal steps, a high-temperature solder, like a high Lead (Pb) alloy melting around 300°C, can be used first. This allows for subsequent soldering with lower temperature alloys, such as Tin Silver (SnAg) at 220°C, and Indium-based solder at 150°C, providing flexibility without compromising device integrity.
Conversely, for applications involving thermally sensitive components, a low-temperature solder is essential. These solders, with melting points below 150°C and sometimes as low as 100°C, protect delicate components from heat damage. The choice of solder is fundamentally driven by its melting point to meet the specific thermal requirements of the process.
Factors to Consider When Choosing Solder
When selecting the right solder melting point for your project, consider the following factors:
Component Sensitivity
The components you’re soldering will dictate the solder’s melting point. Sensitive electronic components, for instance, may be damaged by high temperatures, making a low-melting-point solder preferable. Conversely, plumbing and metalwork projects might benefit from high-melting-point solders that provide stronger bonds.
Application Environment
Consider the environment in which the soldered joint will be used. High-melting-point solders are better suited for high-temperature environments as they maintain their integrity better under heat. For example, automotive or aerospace applications often require solders that can withstand elevated temperatures.
Joint Strength
The required strength of the soldered joint is another crucial factor. High-melting-point solders, like silver solder, create very strong bonds, making them ideal for mechanical applications where the joint will be under stress. For less demanding applications, a standard lead-free or lead-based solder might suffice.
Regulatory Requirements
In some cases, regulations will influence your choice of solder. Many countries have restrictions on the use of lead-based solder due to its toxicity. Familiarize yourself with local regulations to ensure compliance.
Why is the Melting Point of Solder Important?
The melting point of solder is crucial because it determines the temperatures at which the solder will melt and solidify. This affects the soldering process in several ways:
- Process Compatibility: The solder’s melting point must align with the thermal limits of the components and materials involved to prevent damage.
- Reflow Soldering: Higher melting point solders allow for multiple soldering steps without reflowing previous joints, essential for complex assemblies.
- Thermal Sensitivity: Low melting point solders are needed for temperature-sensitive components to avoid overheating and damage.
- Joint Reliability: Proper melting points ensure strong, durable solder joints that can withstand operational stresses without failure.
Selecting the right solder based on its melting point ensures efficient, safe, and reliable soldering processes.
Project Specifics and Requirements
Each project has its own unique requirements, and understanding these will guide your solder choice:
- Electronics Projects: For most electronics, a low melting point solder, like the traditional 60/40 tin-lead, or lead-free alternatives like SAC305 (96.5% tin, 3% silver, 0.5% copper) are common. These solders are easy to work with and minimize the risk of heat damage to sensitive components.
- Plumbing: For plumbing, lead-free solder is a must due to health regulations. Look for solders labeled for plumbing to ensure they meet safety standards.
- Jewelry Making: For fine, detailed work like jewelry, silver solder is often used due to its strength and high melting point, providing durable and aesthetically pleasing joints.
Practical Tips for Soldering
Now that you know how to choose the right solder, here are a few practical tips to ensure success in your soldering projects:
- Clean Surfaces: Make sure the surfaces to be soldered are clean and free of oxidation or contaminants. Use fine sandpaper or a wire brush if necessary.
- Use Flux: Flux is essential for preventing oxidation and ensuring a strong bond. Many solders come with a flux core, but additional flux may be needed for challenging materials.
- Proper Heating: Use the right soldering iron or torch for the job. Ensure it’s preheated to the correct temperature for your chosen solder. Apply heat to the joint, not directly to the solder, and allow the solder to flow into the joint.
Final Thoughts
Choosing the right solder melting point involves balancing the needs of your components, the operating environment, and regulatory requirements. Understanding the properties of different solder types and their applications will help you make an informed decision, leading to reliable and durable soldered joints. Happy soldering!
By considering these factors and tips, you can ensure that you select the right solder for your project, leading to better performance and reliability of your final product.
FAQ
The melting point of 50/50 solder, which consists of 50% tin and 50% lead, is approximately 190°C (374°F). This type of solder is often used in various electronics and plumbing applications.
The melting point of 60/40 solder, which consists of 60% tin and 40% lead, is around 183°C (361°F). This solder is commonly used in electronics and general soldering due to its reliable and easy-to-work-with characteristics.
The melting point of 63/37 solder, which consists of 63% tin and 37% lead, is approximately 183°C (361°F).
Plumbing solder typically melts at around 215°C to 230°C (419°F to 446°F). Lead-free options usually melt between 230°C and 250°C (446°F and 482°F).
Hard solder, also known as silver solder or brazing solder, has a melting point that typically ranges from 600°C to 850°C (1112°F to 1562°F).
The solder with the lowest melting point is typically bismuth-based solder. These solders can have melting points as low as 138°C (280°F). Bismuth-based solders are used in applications where minimizing heat exposure is crucial, such as in delicate electronic components or low-temperature bonding.
Catalog: Materials Guide
This article was written by engineers from the BOYI team. Fuquan Chen is a professional engineer and technical expert with 20 years of experience in rapid prototyping, mold manufacturing, and plastic injection molding.
