Table of contents
- What is soldering?
- What materials and metals can you solder?
- Differences in types of soldering
- Soft soldering
- Brazing
- Induction brazing / high-temperature brazing
- Which soldering processes / soldering techniques are there?
- What do you need for soldering?
- Which flux is the right one for soldering?
- Which tool is needed for soldering?
- What is the difference between welding and soldering?
- Conclusion
Soldering connects metals using solder. Correct soldering creates an inseparable material connection between two metal components - called a solder joint. In the household, soldering is a simple method of repairing cables and electronic parts. However, the joining process is also used in industry for mass production. This guide will tell you what is important.
What is soldering?
Soldering describes the process of joining metals using a metal alloy, known as solder. Under the influence of heat, the melting temperature of the solder is reached without melting the base materials to be joined. The meaning of soldering therefore refers to the joining of usually two metal parts with the aid of a filler material.
Soldering is used to join metallic materials together. Common examples of applications are electrical connections such as copper strands, wires or pipes made of metals and alloys. However, glass and ceramics can also be soldered.
The technique of soldering is also an important foundation in electronics that can be learnt easily.
What do you need to consider when soldering?
Before you start soldering, you should clarify the basic details:
- Which process is the right one? Soft soldering or hard soldering? In the hobby and DIY sector, soft soldering is usually used. This involves temperatures between 180 °C and 250 °C. For hard soldering - usually for large-area applications - 450 °C or more is common.
- Choosing the right solder and flux: Solder does not consist exclusively of tin, but of an alloy of several metals. Its composition influences the flow behaviour and quality of the treated surface. In principle, the flux ensures that the workpiece can be well wetted by the solder. It also removes existing oxides and prevents the formation of new oxides that can occur during the soldering process.
- Use the right soldering equipment: The most common devices for soldering work are soldering irons, soldering guns, soldering stations and gas soldering irons.
Which materials and metals can be soldered?
Low-stress soft solder joints (e.g. soft solders made from 3% copper and 97% tin) are used in electrical engineering and the automotive industry, but are also applied to copper pipes and fittings in water installations, as well as copper sheets and galvanised steel sheets.
The aim of brazing is to produce joints that can withstand higher loads. Areas of application are therefore the joining of metal pipes in installation technology or the brazing of sheet metal and inserts in vehicle construction.
To summarise, the following materials are suitable for brazing:
- Copper (Cu)
- brass (Me)
- Bronze (Br)
- Nickel (Ni)
- Nickel alloys
- steel
- Ferrous materials
- Precious metals
- Stainless steel
- Aluminium (AI)
- Tin (Sn)
- Zinc (Zn)
Can stainless steel be soldered?
Stainless steel is usually processed using soft soldering. The solder only needs to be heated to 180 to 250 °C for this. Although joints made using the soft soldering process are stable and resilient, they are not as strong as those made using hard soldering. If you want to braze stainless steel, make sure you use the right solder. It must also behave optimally at higher temperatures. Silver solder or silver solder rods are well suited for brazing stainless steel.
Can aluminium be brazed?
Aluminium can be soldered with special fluxes and solders.
Can silver be soldered?
Silver can be soldered using silver solder. Jewellers use silver solder to repair, shape or join pieces of jewellery.
Can brass be soldered?
Brass can be processed by soft soldering and hard soldering. As soft soldering produces little stability, it is only used for small parts. Hard soldering, on the other hand, achieves a high level of stability, but requires a high-quality solder.
Differences between the types of soldering
Soldering processes are divided into soft soldering and hard soldering. The application, stability and load-bearing capacity vary. While soft soldering is mostly used in the domestic environment and in electrical engineering, hard soldering is mainly used in industry.
Soft soldering and hard soldering can also be differentiated by the melting temperature. Joints below 450 °C soldering temperature are categorised as 'soft soldering', while techniques above this are considered to be hard soldering.
Soft soldering
Soft soldering is a popular joining method in many areas of electrical, installation and building technology. In addition to electronic components such as D-Sub connectors and circuit boards, this technique can also be used to easily connect copper pipes and rain gutters.
Instructions for soft soldering
To soft solder a copper pipe, you are welcome to follow the steps below. The instructions can also be used for other soft soldering processes.
- To ensure that the solder adheres well, we recommend roughening the pipes to be soldered. This is done using a simple fleece and a little pressure to pre-treat the outside and inside of the pipe.
- Now apply a suitable soldering paste to the inside of the fitting. Use a small brush or cotton bud to do this and then plug the pipe and fitting together.
- Now fix the copper pipe in place using a screw clamp or vice and heat the soldered joint. As soon as the correct temperature is reached, the solder must also be placed in the correct position (between the pipe and fitting) and heated.
- The solder melts and flows into the gap. Now leave everything to rest and cool down - the soldered joint is then ready.
To avoid the usual mistakes when soldering from the outset, please consider the following tips: Make sure you use the correct temperature. The melting point usually varies between 180 °C and 250 °C, depending on the type and alloy of the soft solder. At the same time, the melting point of the solder must be lower than the workpieces to be joined. Otherwise these will also be melted and damaged.
Brazing
Compared to soft soldering, the melting temperatures for brazing are considerably higher and generally also produce a higher strength. In addition, during the soldering process itself, the heat is not applied selectively but over a large area.
What do you need for brazing?
Brazing is based on solders with a high silver and brass content, which typically require higher temperatures of 450 °C and above. As these temperatures cannot be reached with a soldering iron, you need your own soldering torch.
Instructions for brazing
We explain the correct procedure for brazing steel in just a few steps to suit the brazed joint.
- Ensure that the joints are dry and free of rust, dirt, oil and paint residue.
- Bring the soldering torch up to temperature and make absolutely sure that it is neither too low nor too high. A heat of 700 °C is ideal for steel.
- Apply the flux, run your solder wire over the joint and allow sufficient liquid solder to penetrate the solder joint.
- Finally, allow the solder joint to cool. Then thoroughly remove any flux residue.
Induction soldering
Induction brazing does not require a flame and is considered a reliable application that produces fast and precise products, especially in series production. Due to its practical temperature efficiency, induction brazing can also replace both soft soldering up to 450 °C and hard soldering up to 900 °C.
High-temperature brazing
High-temperature brazing (HT brazing) and copper, nickel or cobalt brazing are used to join components made of stainless steel, nickel and other alloys that can withstand high mechanical loads. They are produced flux-free in a vacuum or in an inert gas atmosphere. The working temperature is over 900 °C and the melting point is between 800 °C and 1,200 °C.
What soldering processes / soldering techniques are there?
Based on DIN 8505, soldering processes are divided into soft soldering and hard soldering. If the temperature for soft soldering is below 450 °C, it is between 450 °C and 900 °C for hard soldering. Even higher temperatures are referred to as high-temperature soldering. In addition to the rough distinction, there are also different techniques.
Piston soldering
Piston soldering is a conventional and popular method in electronics. The use of a soldering iron is typical of this technique. Its task is to heat the workpieces and melt the solder. Conventional soldering irons reach a temperature of 480 °C or slightly higher and are therefore used for soft soldering processes.
Flame soldering
Flame soldering is a thermal joining process using a gas burner. The flame melts the solder and then bonds it to the material. The better the thermal conductivity of the materials (e.g. copper and copper alloys), the shorter the heat-up time for flame soldering.
Bath soldering
Bath soldering is another soldering process in which the parts to be joined are heated by a molten solder or salt bath. The solder is placed in the parts to be joined and heated to working temperature in the bath. It is important with this process that the bath is adapted to the sizes of the workpiece.
Wave soldering or wave soldering
Wave soldering, also known as wave soldering, is a special form of bath soldering. Unlike bath soldering, however, not all parts are completely wetted with solder; instead, a wave is created with the help of a pump, which is used to guide and solder the parts to be joined. Wave soldering is a mass soldering process that is applied to electronic assemblies, for example.
Furnace soldering
In furnace brazing, the parts to be joined are heated together with the inserted solder. The oven brazing process allows the air to be evacuated or filled with shielding gas to prevent the parts to be joined from oxidising. Oven brazing also has the advantage of producing stress-free and distortion-free brazing results, as it heats the parts to be joined evenly. In addition, any number of solder joints can be completed in just one work step.
What is electrical resistance soldering?
With this soldering method, the required heat is generated by an electric current. A resistance point is used directly in the component or at the solder joint, to which current is added in order to melt the solder at the contact point. Electrical resistance soldering is mainly used for series production.
Induction soldering
In induction soldering, an inductor surrounds the solder joint and contacts it with alternating current. The alternating magnetic field heats the components and solder joint. Due to its ease of automation, the technology is mainly used in the appliance industry and in vehicle construction.
Reflow soldering
Reflow soldering is also known as reflow soldering. In this process, components and solder joints already wetted with solder are heated to soldering temperature by applying heat. The molten solder joins the components. A typical area of application for this process is electronics, in particular the manufacture of printed circuit boards with SMD components.
Laser soldering
As the name suggests, laser soldering utilises the precise energy of a laser. The non-contact process heats the solder via a laser beam, melts it and fills the joint gap. Laser soft soldering is mainly applied in electronics. It is used as a brazing process in the automotive industry.
What do you need for soldering?
In industry and mass production, highly functional equipment is required to support the special soldering processes, such as oven or wave soldering. It is much simpler in the hobby and household sector:
- Soldering equipment: gas soldering irons, soldering irons, soldering guns, soldering stations
- Solder, lead-free or leaded
- Flux as the core of the solder
- Soldering plates as a base
Solder
Solder is an alloy of different metals whose task is to permanently join two workpieces. The connection should also be conductive, i.e. allow current to flow.
If we take a closer look at the components of solder, we usually find lead in addition to tin. However, due to its dangers to the environment and health, lead is becoming increasingly rare. Metals such as antimony, silver and copper are therefore used in soft soldering. Brazing alloys, on the other hand, contain brass or silver as well as tin. The physical composition of solder can also vary greatly. Solder wire, solder paste and solder rods are conventional forms of solder.
The melting point of solder is defined by its alloy. Solder containing lead, for example, has a significantly lower melting temperature and is therefore easier to process. The melting temperature of the solder is reached at 180 °C - 250 °C for soft soldering. For hard soldering, the temperature is at least 450 °C. Depending on how the brazing alloy is procured, the melting point can also reach almost 1000 °C.
Is soldering with lead permitted?
Solder containing lead has been banned for commercial use for years, or severely restricted in accordance with EU Directive 2011/65/EU. However, soldering with lead is still permitted for home use and is still very popular due to its good melting and wetting behaviour.
Melting temperatures with and without lead
The melting point of the solder varies depending on its alloy. Similarly, the higher the content of tin and other metals and alloys, the higher the melting point.
Here are a few examples: Solder labelled Sn60Pb40 consists of 60 % tin and 40 % lead and reaches its melting point at 183 °C - 190 °C. A Sn95.8AgCu0.7 solder (tin 95.8%, silver 3.5%, copper 0.7%), on the other hand, requires a temperature of 217 °C. Sn99Cu1 solder (tin 99%, copper 1%) only reaches its melting point at 230 °C.
When does solder melt?
Solder containing lead becomes liquid at a temperature of 180 °C - 190 °C. Lead-free solder reaches a temperature of 218 - 230 °C until it melts.
Is a soldered joint conductive?
In addition to a mechanical connection, solder also ensures conductivity. The flux often already contained in the solder is required to optimally wet the workpieces and protects against oxidisation.
Which solder to use for joining circuit boards?
PCBs are joined by soft soldering. Solder should have a suitable alloy and a low working temperature. For lead-free solders, it is therefore best to use silver and copper.
Common problems with solder and suitable solutions
Too little or too much heat are common application errors when soldering. Here we provide you with the necessary basic knowledge for a safe and functional result.
- Too little heat leads to the solder not melting or not melting completely. As a result, the solder does not adhere to the component but sticks to the soldering iron. Too much heat can even damage your components. Therefore, make sure you use the optimum working temperature.
- However, problems with the solder joint can also occur if the correct temperature is selected. If the contact surface is too small, the solder joint will also be too small. Similarly, if the pressure is too low, the heat will not reach the joint. The solution to this is simple: re-solder. And for sufficient time and an optimum contact surface.
- A clean working area is also important to avoid adhesion problems with solder. Therefore, keep your components, soldering iron and solder clean and clean them before use.
- Solder can last a long time if stored properly. However, tests have shown that soldering can deteriorate significantly after around 50 years. You should therefore use new, high-quality solder wires.
Which flux is the right one for soldering?
High-quality solder wires often already contain a flux. This is also referred to as the "soul" in the solder. As this is quickly used up during the soldering process, an additional flux is usually added.
The composition of fluxes varies greatly. Which flux is the right one depends on the workpiece and the nature of the solder.
A practical flux pen is often sufficient for the targeted application of soldering fluid to the circuit board. Conventional soldering water is also an excellent flux for soft soldering copper sheets.
When using flux, you should always be aware of its effective temperature range. This describes the temperature at which the flux is able to dissolve metal oxides and subsequently initiate the wetting of the solder.
What is the role of flux in soldering?
Flux, also known as soldering water or soldering grease, has the task of ensuring oxide-free solder surfaces and prevents the formation of new oxide layers during heating.
Flux type labelling
According to EN ISO 9454 or the old DIN8511 standard, the type labelling of fluxes consists of several letters. The letter F (= flux) characterises the product itself. The second letter describes the material to be soldered (S = heavy metal, L = light metal) and the third the soldering process (W = soft soldering, H = hard soldering).
Example: The designation F-SH 2 indicates a flux for hard soldering with an effective range of 750 - 1100 °C.
Soldering without flux?
Flux-free soldering is also possible. For copper on copper soldering and the use of copper-phosphorus solders, for example, no flux is required. Palladium solder rods, which are already filled with flux in the inner cavity, also do not require any extra flux. Similarly, when brazing under inert gas or in a vacuum, the oxygen is kept away from the brazing joint so that no flux is required.
What tools are needed for soldering?
Different tools are used for brazing depending on the process and workpiece. Here is an overview:
- Solder
- Flux
- Solder pastes
- Soldering stations
- Reflow ovens
- Soldering tips
- Soldering irons
- Desoldering wires
- Desoldering nozzles
- Solder flux removers
- Solder fume extraction
- Solder mask
- Rework tool
Soldering iron
Soldering irons are sometimes the most important tool for hobby electronics engineers. It is used to create permanent mechanical and electrical connections between circuit boards and components. The soldering iron itself usually consists of a replaceable soldering tip, a heating element and an insulated handle.
How does a soldering iron work?
The main task of the soldering iron is to heat the metal parts and the low-melting solder. Soldering irons are usually temperature-controlled to achieve the desired target temperature on the metal part and solder. This can be measured with a temperature sensor mounted near the tip. The temperature-dependent resistance on the heating wire can also be analysed. This means that even temperature-sensitive workpieces, e.g. electronic components, can be optimally processed.
How hot does a soldering iron get?
Soldering irons are soft solder tools. The average soldering temperature for soft solders is between 300 °C and 450 °C.
How is the tip of the soldering iron cleaned?
A clean soldering tip is necessary to maintain the functionality of the soldering iron. Contaminated soldering tips increase the error rate, impair thermal conductivity or make the soldering iron unusable as a tool. The cleaning process itself is very simple. You can either use brass wool or, even easier, a damp cellulose sponge to remove dirt or excess solder.
What is a soldering gun?
A soldering gun is an electric soldering device. As with soldering with a soldering iron, the soldering gun also creates fluid and electrically conductive connections by melting solder. However, the soldering gun is usually preferred in applications due to its better ergonomic shape.
Soldering without a soldering iron and solder?
Soldering without auxiliary equipment such as a soldering iron is possible, but only works to a very limited extent. The challenge is to use a candle or lighter to reach the right temperature in the right place to melt the solder. Make sure you do a test to find out how long you need to heat your metals. You will also need a pointed object to replace the tip of a soldering iron so that you can solder with pinpoint accuracy.
With the help of soldering glue or wire glue, you can completely replace conventional soldering. Electrically conductive adhesives, which can even withstand vibrations and oscillations, can be a better alternative to the classic soldering process, especially for temperature-sensitive objects.
Further questions about soldering: Do you have further questions about soldering? Here we clarify some interesting details about soldering connection technology for you.
What is a cold solder joint?
With a cold solder joint, no connection has been created between the solder joint and the joining material during the soldering process. The result: You have a mechanical connection without conductivity. Vibrations to the solder joint during cooling or excessively high temperatures when adding flux are common causes.
Recognising cold solder joints is not always easy - especially when it comes to the now very common, lead-free solder, which has a rather matt appearance from the outset. Nevertheless, carry out a visual inspection. Cold solder joints usually appear blunt, convex or deformed. You can also detect cold solder joints using a multimeter. Solder joints must be worked out precisely in order to function. Repair cold solder joints by reheating the solder joint with a soldering iron and adding fresh solder. If you do not have the right materials to hand, you can also try to repair the cold solder joint without soldering. This can be done using makeshift materials such as a lighter or conductive adhesive.
Conclusion
Soldering is a basic application in electronics. PCBs, copper pipes and parts in vehicle construction are common examples of applications. In this guide, we have outlined the most important terms and distinctions to help you find the right soldering technique for your task and ensure the desired performance through the soldering process: a connection to conduct heat or electricity.
Despite careful editing and checking of the content, Stecker Express assumes no liability for the topicality, correctness, completeness and quality of the information provided.
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