Considering solders are metal, they obviously conduct heat. But why is it important to know about the thermal conductivity of solder in depth?
There are numerous types of solder, which is a mixture of different metals, on the market. Knowing the solder’s thermal conductivity will help you find the perfect one to meet your needs.
Read along to learn about your solders and get suitable materials for your appliances. This article will discuss different solders and the thermal conductivity of solders.
Understanding Thermal Conductivity of Solder
Solder is an alloy composed of tin and lead. Depending on the ratio of the mixture, the properties of solder can vary, such as melting point, electrical conductivity, thermal conductivity, and more. According to these properties, the application of solder also differs.
The most common use for solders is in joining two or more materials in electronics. Its conveniently low melting point allows you to melt and use it on surfaces.
Along with that, the thermal conductivity of solder is a property that will enable it to act as a heat sink in appliances.
Fourier’s Law
In laymen’s terms, the thermal conductivity of solder is a material’s ability to transfer and conduct heat from a higher heat region to a lower heat region through itself.
Fourier’s Law provides a more technical explanation for this phenomenon, stating that the heat transfer rate and the surface area through which heat is transferred are proportional to its negative temperature gradient.
Different Solder Materials
As mentioned previously, solder is composed of different ratios of materials. The composition of a given solder determines its attributes.
Similarly, you should know which solder suits your purpose. Understanding the composition of this alloy will help you decide which type of solder you need for your project.
Apart from these common alloys, you will find solders with additives; these metals are involved in reducing or enhancing certain specifications of the solder.
Mainly, solders are either lead-based or lead-free alloys. Over time, lead-free solders are recommended for health-related reasons, but obtaining the required thermal conductivity of solder in these alloys has become difficult, so various substitutes have been created.
Thermal Conductivity
Table 1.1 states the metals and their ratios for the composition to make the solder.
Materials in the table are arranged in ascending order based on the Thermal conductivity of the solder. The melting point of each solder material is also mentioned in the table.
The range of melting temperatures between the different materials exists because fixed temperature depends on fixed composition, which can vary slightly.
Table 1.1: Thermal Conductivity of Solders
| Solder | Ratio | Thermal Conductivity (W/mk) | Melting Temperature(˚C) |
| SnAg | 96.5/3.5 | 78 | 221 |
| SnCu | 99.3/0.7 | 65 | 227 |
| SnCuNi | Sn100C | 64 | 227 |
| SnAgCu | 95.6/3.5/0.9or96.6/3.8/0.7 | ~60 | 217 Eutectic~220-217 |
| AuSn | 80/20 | 57 | 280 |
| SnAgCuSb | 96.2/2.5/0.8/0.5 | 57 | 215-217 |
| Snpb | 63/37 | 50 | 183 |
| AuGe | 88/12 | 44 | 356 |
| AuSi | 97/3 | 27 | 363 |
| Pbln | 50/50 | 22 | 209 (liquid) /180 (solid) |
| BiSn | – | 19 | 138 |
| Pbln | 80/20 | 17 | 280 (liquid) /270 (solid) |
Cited from: https://www.electronics-cooling.com/2006/08/thermal-conductivity-of-solders/
Applications of Solder
Now that you are aware of what thermal conductivity of solder is and how the mixture of metals can change it, read on to learn more about the applications for low and high thermal conductive solders.
Step Soldering
You probably already perform step soldering without even knowing it. Solder materials with low thermal conductivity are usually used for step soldering. It is a process of layering solder material, starting from the inside with a low melting point and working your way out with an even lower melting point.
It is common to wonder what temperature gap you should use for step soldering. You have to be careful since you don’t want your first layer of solder to be melted away when you apply the upper-level solder.
At a minimum, there should be a temperature gap of at least 25˚C between the melting points of different soldering materials.
Heat Sinks
A major application for high thermal conductivity of solder is creating heat sinks in devices. Since we know that the thermal conductivity of solder is a characteristic that allows for heat transfer, the greater the thermal gradient, the quicker rate we get for our heat relay in our devices.
A heat sink is where the solder material with high thermal conductivity is applied to attach parts within a device where heat needs to be dissipated. Heat sinks are a necessity in devices that expel high temperatures while working, such as a CPU.
Soldering alone does not work as a heat sink, but it is used as an interface between the aluminum/ copper heat sink and the device which produces heat.
Soldering Joints
Soldering joints is a simple yet important use of solders. Solder has been used to melt and join electrical devices and wires. A man with no electrical engineering skills is also using soldering to connect wires in their day-to-day life.
Commonly, an alloy with a low melting temperature is preferred. The thermal conductivity of solder may or may not be vital for this use. While connecting wires, a basic alloy that you would find in the market will work fine.
However, if you must join parts that dissipate heat and you need that heat to transfer from one part to the other, then thermal conductivity is important.
Final Analysis
Now that you know the information detailed above, you are fully equipped with the knowledge of the thermal conductivity of solders. You also now know how to look for a soldering material to meet your needs.
Before getting the soldering material, identify the main purpose. You should know where the material is being used to get the correct alloy.
If you are looking to attach parts that need cooling, then a high thermal conductivity solder is what you need. On the other hand, if you are undertaking the simple task of connecting wires, feel free to buy yourself a commercial soldering alloy.
