What you need to know about solder powder to achieve ideal results

Solder powders – or solder metal powders – are an alternative to the classic method of soldering using a wire. While hobbyists and do-it-yourselfers have already incorporated solder powder and the pastes made from it into their repertoire, some industrial users are still sceptical about the whole thing. For this reason, we are now going to answer the most important questions on solder powder to enable you to achieve the best-possible results when using it.

Solder powder: A real alternative to solder wire?

In recent years, solder powder has been used more and more frequently in place of typical tin solder in industrial applications. However, questions will crop up on the ideal processing method precisely when the existing processes at your company are to be switched to using solder powder – or when you want to integrate a completely new soldering process. Despite the fact that the basic principle of soldering remains the same, there are still a few things you should keep in mind when switching to solder powder.

What types of solder powder are there?

Solder powders are almost exclusively alloy powders. Irrespective of the type of soldering concerned, both lead-free and lead-based solders are used. Typical characteristics that distinguish the different types of solder powder include:

• Material composition: The following are examples of common solder powders:
  • Sn96,5Ag2,5Cu0,5
  • Pb70Sn30
  • Pb63Sn37
  • Pb60Sn40
  • SAC305
  • SAC405
• Grit size: Two typical grit sizes, <63 µm and <150 µm, are commonly found amongst aluminium-silicon solders. In the case of soft solders, such as SAC305, for example, a distinction is made between types T3, T4 and T5. T3 ranges from 45-25 µm, T4 from 38‑20 µm and T5 from 15-25 µm. Common values for lead/tin solders are <45, <63 and <75 µm.
• Grain distribution: A grain distribution which remains constant helps you to establish a stable soldering process.
• Oxygen content: Keeping the oxygen content of the solder powder as low as possible is another factor which contributes to the success of the soldering process. This allows the amount of flux used to be reduced.

Normally, a solder powder is not used in its pure form but as a solder paste. This paste is created by adding a suitable flux. This is also needed to join parts together in the desired fashion using conventional soldering methods.

Where can solder powder be used?

As is the case when soldering using tin solder wires, solder powder can be used for both hard soldering and soft soldering purposes. This means that it can be used across a wide range of industries and applications.

Hard soldering

For hard soldering carried out at hotter temperatures of around 590° C, aluminium-based solder powder is a much-favoured solution. Other hard solders are made of silver, brass and phosphorus, for example. Among other things, powder-based hard soldering is suitable for saucepans with a stainless steel bottom and for heat exchangers in the automotive industry.

Soft soldering

In the case of soft soldering, solder powders based on a combination of tin, silver and copper, which melt at temperatures of around 250° C, are popular. These solders are primarily used in the electronics industry for manufacturing sensitive components using surface mount technology (SMT).

How is solder powder used?

Depending on the type and composition of the solder powder in question, various aspects need to be taken into consideration during processing. This is the only way of ensuring that work can be carried out safely whilst guaranteeing perfect results. These are some of the decisive factors:

• Ideal soldering atmosphere: What does the current soldering atmosphere look like, respectively, do you need to adjust the atmosphere to your preferred solder powder? It might be just as possible to do the soldering in a vacuum environment as using inert gases, hydrogen or dissociated ammonia.
• Type of flux: Which flux is the right one for your solder powder and the soldering process you have in mind? In addition to multi-purpose fluxes, there are also special fluxes for tin-aluminium alloys, stainless and high alloy steel and nickel and copper hard solder powders. Some fluxes are only suitable for soft or hard soldering. In the case of some fluxes, the solder joints need to be cleaned after soldering, otherwise corrosion may set in – causing damage to the component in the long term.
• Soldering scope: Is the desired alloy designed for the required temperatures? If the alloy needs to be heated too strongly, the components may be damaged. The real advantage of soldering compared to welding, for example, would then be lost.

What are the advantages of solder powder?

If you take all the important properties of solder powder into account, there can be virtually no objections to using it at your company. This is because the use of solder powder has one decisive advantage over the use of classic solder wire. The powder, respectively solder paste, makes it easier to automate the soldering process. The solder material and flux are simply applied in one step as a blended solder paste instead of one after the other.

The amount of flux always stays the same, as long as no mistakes are made when mixing the solder paste. This guarantees that the quality of the solder joints remains constant – without the need for readjustment. It is easy to apply the right amount of solder paste, thus simplifying the automation of the process. This means that you can use solder powder at your company to achieve a more efficient production process. The one-time conversion – and possible retrofitting of your machines – quickly pays off.

Solder powder – a true all-rounder

Solder powder offers you numerous options when it comes to joining components together. It is in no way inferior to its big brother, the solder wire. Whether you use a ready-made solder paste or create your own individual blend using your ideal solder powder and the flux of your choice depends on your individual expertise, the requirements and what your company is capable of achieving. The individual composition of a suitable solder powder which is customised exactly according to your needs can raise quality to a new level and open up new avenues.