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This is how you succeed with your soldering!

Some practical tips

Basic technique

Heat both surfaces that are to be soldered using the soldering tip before the tin is applied. This will prevent cold solder joints, which means the tin only adheres to one surface. Melt a little tin on the soldering tip beforehand (pre-tinning) so as to speed up the heating process. In some cases tinning the surfaces to be soldered will also make things easier.

Find the right balance

Do not heat longer than necessary. This increases the risk of destroying both components and conductive paths, and the risk of producing a poor and dry soldering. A poor soldering can be recognised by shrunken or deformed tin with a matt finish. A good soldering has a smooth and glossy pyramid shape. The trick is to find the right temperature as quickly as possible to produce a perfect soldering, without running the risk of damaging components.

Use soldering tips of the right size

The tip should be as close as possible in size to the joint being soldered in order to achieve the best possible energy transfer and long service life.

Select the right temperature

The right temperature means that it is as low as possible. If you are using lead-free solder, the temperature should not exceed 385°C. Excessive temperatures compromise the quality of the soldered joints and cause the soldering tips to oxidise too quickly. A soldering station with set-back function is a good choice. Set-back automatically reduces the temperature when the tool is not in use and extends the service life of the tips.

Clean the tip correctly

The tip should always be cleaned before soldering, not after. Use steel wool or a sponge. The sponge should be damp but not wet.

Tin the tip after cleaning

To avoid oxidisation, the tip should always be tinned directly after cleaning. Oxide on the tip significantly reduces energy transfer.

Flux material

The main function of the flux is to counteract oxidisation and to make the tin more fluid so that it flows correctly on the soldering surface. This is known as wetting. Too little flux results in poor and unreliable soldering. Sometimes this causes problems immediately, or problems may occur at a later date because insufficient wetting shortens the life of the soldering joints. However, flux residues can easily cause corrosion and must be removed after soldering.

Lead-free soldering

In certain respects, there is no real difference between lead-free soldering and conventional soldering. In other respects, however, lead-free soldering poses considerable challenges. When carrying out service and maintenance work using hand tools, the soldering techniques are largely the same. In the case of large-scale production with smaller components and thinner circuit boards and conductive paths, the problems are somewhat greater. The biggest concern is the higher melting temperature of lead-free solder – not least when working with small components where it can be particularly challenging to strike a balance between the solder’s melting temperature and the temperature that the components can withstand. The solder’s ability to flow, or its wetting capability, is also poorer in lead-free solder. A lead solder has a melting temperature of around 183°C, while lead-free only melts at around 217°C.

SMDs – surface mounting

Soldering small surface-mounted components by hand is a little more complicated, but entirely possible. To start with, you need one hand to hold the component in place. So conventional soldering using a soldering iron while holding a solder wire against the joint being soldered can be difficult to perform. It is easier to melt enough solder beforehand on the soldering tip. What happens then is that all the flux in the solder evaporates away. This is why you also have to add flux to the soldering pads beforehand. In many cases, soldering tweezers are excellent to use.

An alternative method is to use hot air. When soldering with hot air, soldering tin in paste form is used, which is positioned beforehand on the soldering pads. To a certain extent, the paste also helps to keep the components in place. Difficulties of using hot air include the problem that components are easily blown away if the airflow is too h3 and there is a risk that other components may be burned and destroyed, in tightly packed circuit boards for example. In such cases it can be necessary to use very precise equipment with a low airflow and small nozzles. The problem here can be in reaching the correct solder temperature quickly enough to be effective before the component being soldered is damaged by the heat. A preheater system can be used in such cases – essentially a heating plate that heats the entire circuit board to a higher starting temperature.

Many factors will determine which method is the most suitable in the given circumstances, but you often need to have access to and master both methods.

Extremely small components

When we look at the smallest sizes of surface-mounted components, for example 0201 and 01005 in size, other factors come into play. Capacitors of this size in particular are extremely sensitive to thermal shock. It is not just high temperatures that are critical; the speed with which the temperature is increased is also important. Put simply, the capacitor is at risk of cracking if the temperature changes too quickly. A normal specification for such a capacitor is a maximum of 265°C with a maximum temperature increase of 6°C/second. By comparison, the increase in temperature where a soldering iron is applied directly to the capacitor would be around 125°C/second. The only option here is hot air combined with a preheater.