Solder and flux selection for electronic circuits (2023)
Solder wire is the filler material that helps in joining components with the circuit board when heated and on the other hand flux is a compound that removes the oxidation from joints as well as from soldering iron. Flux also improves the wetting property of solder.
The selection of solder wire and flux for electronic circuits is crucial. Solder wire has different types with different diameters and compositions and flux also has several types with different applications. All these factors should be considered before selection along with compatibility and safety considerations.
This article will guide you through the factors to consider in solder and flux selection for circuits to ensure high-quality soldering results and optimal performance in your electronics projects.
Let’s get started.
Solder wire
Solder wire is a type of metal alloy used in electronics to join two metal surfaces together. It is typically composed of lead and tin, there are also lead-free solder wire which is composed of tin, silver, and copper.
Let’s discuss the factors that will help you in considering solder wire for your electronics circuit.
1. Types of solder wire
There are many types of solder wire, each one with its characteristic and applications.
a. Leaded solder:
Leaded solder has lead in its composition which is combined with other metals like tin. It has a typically low melting point that makes it reliable to work with.
Leaded solder is the best option for electronic circuits, but the presence of lead is considered unhealthy for the environment and also for the person working with it.
b. Lead-free solder:
After considering the health hazards of lead, industries move towards lead-free solder. As the name suggests this type of solder doesn’t contain lead in its composition.
The melting point of this solder is high as compared to leaded solder, so it is a little difficult to work with it but usually that not a big problem. Lead-free solder is a good alternative to leaded solder for electronic circuits.
c. Rosin-core solder
Some solder wire has flux in its core. As flux is important for cleaning joints and improving the flow of solder. Rosin-core solder contains flux in its center.
This eliminates the need for extra flux. There is also acidic-core solder which is used for plumbing so for electronic circuits the rosin-core solder is used.
The main types of solder are leaded solder and lead-free solder both are used in electronics, but it is a bit easier to work with leaded solder. Also, avoid the use of acidic-core solder for electronic circuits.
2. Alloy composition
The second factor that should be considered is alloy composition means the solder wire has which metals in its composition.
The Sn-Pb solder wire has 60% tin and 40% lead and is suitable for electronic applications. The 63/37 is also generally recommended.
Due to the environmental concern of leaded solder, lead-free solder is preferred which has tin, copper, and silver in its composition.
3. Diameter
The selection of the diameter of the solder wire depends upon the application or type of project you are working on.
The thick wire will be suitable for soldering large components or through-hole connections, while finer wires are ideal for delicate surface-mount components.
For most electronics application, the solder wire range from 0.4 to 1.0 mm work fine but for surface-mounted devices then this range can be lowered.
4. Flux core
Solder wire has two types of cores solid core and flux core. Flux core is mostly recommended for electronics applications as it provides an appropriate amount of flux to ensure better wetting and reliable solder joints.
In solder wire, the flux is at the center of the wire and helps in removing oxidation from the soldering surfaces.
Flux
Flux is a material used in soldering to improve the quality of the solder joint by facilitating the soldering process and ensuring a reliable and durable bond between the solder and the metal surfaces being joined.
Flux has several functions, it removes oxidation and other contamination from the surface being solder, improve the wetting and flow of molten solder and act as a temporary protective barrier on metal surface during soldering.
Here are the key considerations for selecting flux.
1. Type of flux
There are three types of flux rosin-core, water-soluble and no-clean flux.
a. Rosin-core flux
Rosin-core flux also known as rosin or activated rosin, is the most commonly used flux in electronics applications. It is a natural resin obtained from pine trees.
Rosin-core flux is generally available in liquid, pen flux and flux core solder wire. Rosin flux is known for its excellent wetting properties and its ability to remove oxide layers from metal surfaces during soldering.
It leaves a non-conductive and non-corrosive residue that is mostly not harmful to electronic components when properly cleaned. The flux is typically used for soldering electronics components, circuit boards and small electronics connections.
b. Water-soluble flux
Water-soluble flux is a type of flux that is easily removed with water after soldering. It is usually necessary for applications where flux residue must be removed.
It is available in various forms, including liquid flux and flux paste. Water-soluble flux provides good wetting properties and effectively removes oxide layers, promoting reliable solder joints.
c. No-clean flux
No-clean flux is a type of flux that does not require cleaning after soldering because it leaves minimal residue. It leaves a residue that is non-conductive and non-corrosion.
The application where this flux is densely populated circuit boards or sensitive electronic components or where the cleaning is difficult.
These are the three types of flux each one used for different applications. For electronics circuits and applications rosin-core flux is recommended due to its non-corrosive property and effectiveness for a variety of electronics applications.
2. Activity level
Flux is also available in different active levels such as rosin (R), rosin activated (RA) and rosin mildly activated (RMA). The different active levels of flux determine how effectively remove the oxidation and promote the wetting property.
Flux having high active levels are better for soldering surface and remove more oxidation or contamination. The activity level should be considered while selecting flux.
3. Application methods
Applications methods also define which flux will be best for you. Flux is available in liquid, paste, and pen form. Considered the form of flux which is suitable for your application and also that is easy for you to work with.
Conclusion
The appropriate selection of solder wire and flux in soldering is important. For strong, clean and reliable joints these two things are essential.
Choosing the right solder wire depend upon some key factor such as alloy composition, diameter, and flux core. The type of project you are working on also defines which solder wire will be best.
Flux is essential as it improves wetting and enhances the flow of molten solder. The type of flux, activity level and application methods keep these factors in your mind while selecting flux for your electronic circuits.
Remember to follow safety guidelines and best practices when soldering to ensure successful outcomes.
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