HowTo: Electronics - My friend the soldering iron

Even as a part-time nerd, you can't really avoid the soldering iron in the long run. At the latest when the first test circuit on the breadboard has worked well and you want to take the next circuit evolutionary step, it's time to wield the soldering iron.

As a child, I had a terrible respect for this thing for a long time. It's hot, it smells and smokes and as a layman you always have a half guilty conscience about whether what you're doing is right.

I still have respect now. And I think that's entirely appropriate. Because you can still break a lot when soldering. Both on your own body and in the circuit to be built or repaired.

When soldering, a lot depends on the dosage. Not only must the temperature be right, but some components must not be heated too much. At the same time, however, there must be enough temperature to connect the component electrically - and often also mechanically sufficiently - to the carrier board (PCB). This also includes the right solder, which should be applied sufficiently. But again, it's all about the dosage: too little and the component falls off. Too much and the component holds very well, but there may be short circuits.

As you can see, there are a few pitfalls waiting for you. To give you an easy introduction to the world of soldering, here are a few tips on the right choice and correct handling of the soldering iron.

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Safety instructions

I know the following notes are always kind of annoying and seem unnecessary. Unfortunately, many people who knew "better" have lost eyes, fingers or other things due to carelessness or injured themselves. Data loss is almost negligible in comparison, but even these can be really annoying. Therefore, please take five minutes to read the safety instructions. Because even the coolest project is not worth injury or other trouble.
https://www.nerdiy.de/sicherheitshinweise/

Affiliate links/advertising links

The links to online shops listed here are so-called affiliate links. If you click on such an affiliate link and make a purchase via this link, Nerdiy.de will receive a commission from the relevant online shop or provider. The price does not change for you. If you make your purchases via these links, you support Nerdiy.de in being able to offer other useful projects in the future. 🙂 

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Requirements

Helpful articles:
You can also find additional information on various soldering techniques in the following articles.
Electronics – Solder SMD components by hand
Electronics – Solder THT components by hand

Required material:

In the following list you will find all the parts you need to implement this article.

Required tool:

In the following list you will find all the tools you need to implement this article.

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Security

Words about safety are often overlooked because safety measures are only accepted as necessary once you have already been injured. To prevent this from happening, here are a few words of warning 🙂

There are basically three and a half serious dangers when soldering:

1. the tip of the soldering iron becomes very hot. This generates temperatures of 200-500°C. There is therefore a considerable risk of burns. So make absolutely sure that you do not touch the tip and the metal parts connected to it. Also take special care not to leave the (hot) soldering iron alone with children. Especially forbidden things often make children curious.

2. the hot tip not only has a considerable potential for injury. It can also cause fires. Never leave the soldering iron switched on/hot unattended. Under favorable conditions, a fire can spread so far within a minute that it can no longer be easily extinguished.

3. In dem normalerweise verwendeten Lötzinn ist eine Seele aus Flussmittel enthalten. Dies ist notwendig/nützlich, denn es begünstigt den Verbindungsprozess des Lötzinns mit den Metallen der jeweiligen Kontaktflächen. Manchmal kann es dadurch aber auch vorkommen, dass das Lötzinn „spritzt“ also teile davon unkontrolliert umherfliegen. So make sure that you do not have any sensitive parts (e.g. smartphone display) in the immediate vicinity that could be damaged during the soldering process. Although safety goggles are also annoying here, they are much less annoying than a serious eye injury.

3.5 Various vapors and gases are produced during the soldering process and especially during the melting of the solder. Make sure that these gases are either extracted or that the room you are working in is well ventilated. A combination of both is best. While soldering, you can also try to blow away the rising soldering fumes. In any case, you should avoid inhaling the soldering fumes.

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Set-up and correct position of the soldering iron

A soldering iron is actually always built according to the same principle. You can see a simple soldering iron that can even be operated via USB in the following picture.

1. tip

The tip of the soldering iron is at the front end. It is usually interchangeable and available in different sizes and shapes. There are tips that are very suitable for soldering SMD components and also tips that can be used to solder guttering 🙂
The tip of the soldering iron is also usually specially coated so that the solder adheres to it - at least a little. The tip should also be cleaned well before each soldering process. But more on this later.

2nd heating cartridge

Directly after the tip is another metal tube. This usually contains a heating cartridge and a temperature sensor, both of which are thermally coupled to the tip of the soldering iron. This ensures that the metal tube, heating cartridge, temperature sensor and tip always have the same temperature. With the help of the temperature sensor, the temperature of this (heating) unit can be regulated to within a few °C on many soldering irons.

3. handle

The handle allows you to guide the tip of the soldering iron properly. It insulates you from the high temperatures of the heating unit and usually has a rubberized surface for a good grip. The handle is also the only part of the soldering iron that you should touch.

4. connecting cable

The connecting cable hangs as a more or less annoying appendage at the other end of the soldering iron. It supplies the soldering iron with the necessary energy to bring it to the desired temperature. The current values measured by the temperature sensor are often fed back to the soldering station. Here you should always make sure that the cable is not kinked or knotted. In addition, it should of course not come into contact with the hot soldering tip.

Holding the soldering iron:

Holding the soldering iron is actually quite easy. Hold this like a pen you want to write with. Hold it as close to the front of the soldering iron handle as possible. Of course, make sure that you do not accidentally touch the hot tip of the soldering iron.

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Soldering iron vs. soldering station

Die „Lötkolben vs. Lotstation“-Frage lässt sich gar nicht so pauschal beantworten. In den meisten Fällen reicht tatsächlich ein ganz normaler Lötkolben. Solltet Ihr bereits einen Lötkolben zuhause liegen haben und nur gelegentlich nutzen, um zum Beispiel Leitungen zu verbinden, so braucht Ihr Euch keine neue Lötstation kaufen. Die meisten Vorteile von Lötstationen offenbaren sich meistens erst wenn man regelmäßiger zum Lötkolben greift oder speziellere Aufgaben damit bewältigen will.

The main advantages of a soldering station over a standalone soldering iron are:

• The soldering irons (handpieces) are often lighter
• The cables are longer and more flexible, making them easier to work with
• The temperature can be set (more precisely)
• Display of the current temperature is possible
• Earthing connection for protection against ESD is possible
• Many soldering stations have an integrated (stable) holder for the soldering iron including a holder for a cleaning sponge

Ihr seht das sind alles keine „Killerargumente“ gegen den Lötkolben. Lediglich in dem Fall, dass Ihr Bauteile verlöten wollt die sehr kritische Temperaturanforderungen haben kann es zwingend notwendig werden eine Lötstation mit einstellbarer Temperatur zu kaufen. In den meisten anderen Fällen ist die Lötstation einfach die luxoriösere Version eines Lötkolbens.

You will only need a soldering iron with a very fine tip for special (very small) SMD components. Due to this possibly forced new investment, most people end up with a soldering station at the latest.

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Soldering with hot air

In addition to soldering with a soldering iron (also known as contact soldering), there is also the option of soldering components with hot air. The entire component including the circuit board is heated and the previously applied solder or solder paste melts into the circuit board and component.

This is usually used when soldering SMD parts. You can find information on this in the article Electronics – Solder SMD components by hand

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Power of the soldering iron

Neben dem einstellbaren Temperaturbereich bzw. der Temperatur des Lötkolbens ist auch die Leistung ein nicht zu vernachlässigender Faktor. Denn während die Temperatur angibt wie Heiß die Spitze bzw. das damit (thermisch) verbundene Lötzinn/Lötpad/Bauteil/Leitung wird, gibt die Leistung (im übertragenem Sinne) an wie schnell diese „Hitze“ nachgeliefert werden kann.

This is because every metallic part that is thermally connected to the tip of the soldering iron draws heat away from the tip. The larger this part is (e.g. a large mass surface), the faster this heat is dissipated. If this happens faster than the soldering iron is able to dissipate the heat, the tip and therefore the parts to be soldered will no longer reach the desired temperature.

In this case, the component to be soldered acts as a heat sink for the tip of the soldering iron. If the power of the heat sink (i.e. the ability to dissipate thermal energy) is greater than the thermal energy supplied to it (by the soldering iron), the coupled system of soldering iron and heat sink becomes colder overall and not warmer.

You will notice this quite quickly when the solder melts very well at the tip of the soldering iron, but then bonds very poorly to the component or conductor/solder pad. This is because the soldering iron does not manage to heat the conductor/solder pad quickly enough to the melting temperature of the solder. In this case, often only more power will help. Sometimes, however, you are lucky and it is enough to increase the set temperature of the soldering iron slightly. Provided you have the option of adjusting the temperature and the components used can withstand the higher temperature.

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Duration of the soldering process

In short, a soldering process should always be as short as possible but as long as necessary.

Ihr solltet es also vermeiden Bauteile zu „braten“. Falls Ihr euch unsicher seid, welche Temperaturen das von euch verwendete Bauteil aushält, könnt Ihr auch einen Blick in das entsprechende Datenblatt werfen. Dort sind die erlaubten Temperaturen mit den jeweiligen Wirkdauern aufgeführt. Im Zweifelsfall lasst Ihr das Bauteil zwischen den „Lötversuchen“ einfach etwas abkühlen bevor Ihr den nächsten Versuch startet.

You should also be careful with solder pads on printed circuit boards (PCBs). These can detach from the PCB due to high and prolonged exposure to temperatures. This also helps here: If in doubt, let everything cool down a little, get a fresh cup of coffee and then try again 🙂

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Solder/soldering tin what is useful, what is permitted and how much is necessary

Lot – oder umgangssprachlich auch Lötzinn oder Lot-draht genannt – ist beim Löten im Prinzip „der Klebstoff“ um zwei andere Metalle miteinander zu verbinden. Natürlich ist das Prinzip des Lötens und des Klebens vollkommen unterschiedlich, aber es veranschaulicht ganz gut wozu das Lötzinn beim Löten benötigt wird. Eine gute Lötverbindung führt im Idealfall dazu, dass zwei Metallteile(z.B. zwei Kabelenden) elektrisch und thermisch (manchmal auch mechanisch) stabil miteinander verbunden werden.

Damit das Lötzinn seiner verbindenden Aufgabe nachkommen kann muss es zuvor erhitzt werden. Dazu ist es wichtig, dass die Schmelztemperatur der zwei zu verbindenden Metalle(z.B. zwei Kabelenden) geringer als die des Lötzinns ist. Diese verringerte Schmelztemperatur wird dabei durch eine spezielle Mischung aus verschiedenen Metallen – auch Legierung genannt – erreicht. Das geschmolzene Lötzinn fließt dann in alle zwischen den Metallteilen bestehenden Ritzen und verbindet diese miteinander. Daher kommt auch der Name „Lötzinn“, denn viele Lot-Legierungen enthalten oft zu einem Großteil das Metall Zinn.

This brings us to the first important property of soldering tin: The alloy. This is because it determines an important property of our solder: the melting temperature.
Die Zusammensetzung des Lötzinns ist immer mit angegeben aber leider nur etwas „verschlüsselt“ lesbar. Ein paar Beispiele:

• Sn60Pb40
• Sn50Pb49Cu1
• Sn99Cu1

This information is used to specify the composition of the respective solder. The abbreviated name of the element or metal is always given first, followed by the relative quantity. For example, if you have a solder that begins with Sn60Pb40, this means that 60% consists of tin (Sn) and 40% of lead (Pb). Sometimes the second relative quantity is also omitted. This means that the latter element fulfills the remaining quantity. Sn60Pb40, for example, is the same as Sn60Pb.

Another property of soldering tin is the diameter. Especially when soldering very small components, such as SMD components, it makes sense to use a very fine solder wire. To be prepared for most soldering applications, it is often sufficient to have a normal and a very fine solder wire in stock.

Ein „sehr feiner Lötdraht“ wäre dabei ein Durchmesser von 0,3-0,5mm.
Ein „normaler Lötdraht“ wäre ein Durchmesser von ~1mm.

Another important characteristic that you should consider when buying solder is that it must have a Flux core versehen ist. Im Prinzip ist ein Löt-Draht nämlich kein „Draht“ sondern ein „Rohr“ nur halt in einem sehr kleinen und dadurch schlecht sichtbarem Maßstab. Dieses Rohr ist im Inneren mit Flussmittel gefüllt, welches die Fließeigenschaften des Lots verbessert. Ohne dieses Flussmittel – welches beim Löten oft vollständig verdampft – würde das Lot viel schlechter zwischen die zu verbindenen Metalle fließen und sich mit diesen verbinden. Achtet also immer darauf, dass das von Euch verwendete Lötzinn auch etwas Flussmittel enthält.

The following is a close-up of the flux center core in a solder wire.

With the Quantity of solder gibt es eine ähnliche Regel wie bei der Zeitdauer des Lötvorgangs. Zur Menge gilt auch hier „soviel wie nötig aber so wenig wie möglich“. In Produktionen versucht man die eingesetzte Menge des Lötzinns so gering wie möglich zu halten, da so auch die Kosten so gering wie möglich gehalten werden. Dieses Argument ist im Normalfall für den Heimanwender zwar nicht so kritisch, trotzdem sollte man auf dem heimischen Bastelltisch wenn möglich auch sparsam mit dem Lötzinn umgehen. Aber woran macht man die perfekte Menge an Lötzinn fest?

This is best explained using a few examples and pictures. You can find these in the section „Beispiele von schlechten und guten Lötstellen“ below and in the articles Electronics – Solder SMD components by hand and Electronics – Solder THT components by hand.

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The right carpet pad

Another thing that I personally find important is the base used. When soldering, you sometimes heat up the circuit board, vias and other points so much that the base underneath is quickly affected.

You should therefore make sure that you do not use an easily flammable or deformable base made of plastic or similar. A metal base is also not always suitable because it could draw heat from the point to be soldered on your circuit board.

So if you don't have any unusual requirements for ESD protection for your project, I recommend a simple solid wooden board. Of course, it's not really non-flammable, but you have to leave the (switched on) soldering iron unattended for a very long time before such a wooden board burns. And that's something you generally shouldn't do 🙂

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Board holder, third hand and co.

It is also often recommended that PCBs and the like should be clamped in special holders or locked in some other way during the soldering process. However, none of these holders are really convincing. At least not for soldering components onto a circuit board. The holders often make handling the board more complicated than without the holder. This is because in order to solder components, you first have to insert them through the board from above so that you can then solder them from the other side. As a result, the board has to be constantly removed from the holder and reinserted.

Wie es mit „Hausmitteln“ auch einfacher geht ist im folgenden Beschrieben.

In my opinion, the best way to attach components to a circuit board before soldering is with a piece of tape or adhesive tape.

Simply insert the component at the desired position from above through the circuit board and secure it with a small strip of adhesive tape.

You can then turn the circuit board over and solder the component contacts to the circuit board.

Falls jemand beim Löten doch eine „dritte Hand“ benötigt, empfehle ich die Folgende. Der große Vorteil bei dieser ist nämlich, dass man sie an der Tischplatten-Kante festklemmen kann. Somit fällt die Halterung nicht um und bietet deutlich besseren Halt als die freistehenden Halterungen.

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Temperature is important, too much is bad

The right temperature is a bit of a double-edged sword. Of course, it has to be high enough to melt the solder. Without molten solder, the solder will not work.
However, the disadvantage of the high temperature is that it is also transferred to all metals that are connected during the soldering process. For example, if you want to solder an SMD component to an SMD pad, the solder as well as the SMD component and the SMD pad are heated to the set soldering temperature during the soldering process.

Manche Bauteile können mit dieser „thermischen Belastung“(hohe Temperatureinwirkung) gut umgehen, manche dagegen weniger. Pauschal ist es also ratsam den Lötvorgang so kurz wie möglich aber so lang wie nötig zu halten.

You can often find information on the maximum permitted soldering temperatures in the data sheets of the respective components. For example, the following two images are excerpts from the data sheets of the WS2812B RGB LEDs.

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Cleaning the soldering iron

An important prerequisite for a successful soldering process is a clean soldering iron tip. Especially when it comes to delicate soldering work such as SMD soldering, you should make sure that your soldering tip is cleaned before each soldering process.

Durch vorherige Lötvorgänge setzen sich nämlich schnell Lot- und Flussmittelreste ab, welche den Wärmeübergang und manchmal sogar die Sicht auf das „Operationsgebiet“ erschweren.

There are basically two ways to clean the tip.
The first option is a damp sponge on which the residue can be wiped off at the tip. To do this, draw the soldering iron over the moistened sponge a few times from front to back.

Die zweite Möglichkeit Besteht aus so genannten „Trockenreinigern“ welche sehr stark an Metall-Spülschwämme erinnern. Bei diesen wird der Lötkolben einfach zwei bis drei Mal in die verflochtenen Metallfasern getaucht bis die Spitze sauber ist.

IMPORTANT: The tip of your soldering iron is specially coated, so you should never use sandpaper or a file on it when it is cold. Otherwise you may remove/damage the coating and the solder will no longer hold on to the tip.

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Cover critical areas

In some cases, it can be useful to cover certain unused parts of the PCB with adhesive tape. This protects sensitive other components from solder or flux splashes. Which at best can look ugly and at worst can result in short circuits and destroyed components.

Dazu eignet sich fast jedes Klebeband. Wenn Ihr dagegen auf Nummer Sicher gehen wollt, empfielt es sich „Kapton-Tape“ zu verwenden. Dies ist Temperaturbeständig und lässt sich auch wieder leicht ablösen.

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Cleaning the solder joints after soldering

After soldering components to printed circuit boards, flux residues often remain in the form of dark yellow/brown impurities. These are not tragic from a mechanical and electronic point of view, but often look unattractive or unprofessional.

But there is an easy way to remove them. Alcohol dissolves the dirt very well. Simply put a drop of isopropyl alcohol on a cotton bud or cloth and use it to remove the dirt.

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General procedure during soldering

In the articles Electronics – Solder SMD components by hand and Electronics – Solder THT components by hand ist das verlöten von THT- (also „Durchsteck“) und SMD-Bauteilen im Einzelnen näher beschrieben. Im Allgemeinen lässt sich aber jeder Lötvorgang in folgende Schritte einteilen.

1. Determine the maximum soldering temperature of all components involved in the soldering process and (if possible) set it on the soldering iron.
2. Heat up the soldering iron and clean the tip.
3. Prepare a suitable solder adapted to the size of the solder joint.
4. Mechanically connect the components to be joined (if possible). In other words, position them with holding aids or adhesives so that the metal surfaces to be soldered are in contact with each other.
5. Apply some solder to the tip of the soldering iron. This facilitates the heat transfer from the tip later on.
6. If possible, hold the tip of the soldering iron to both metal surfaces so that both are heated simultaneously.
7. Melt as much solder on the heated metal surfaces - not at the tip of the soldering iron - until both metal surfaces are fully bonded together.
8. Remove the soldering iron and allow the solder, component and circuit board to cool down.

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Simple exercises and tips

Extend/connect cable:

Das verlängern und verbinden ist bei vielen Bastelarbeiten das „täglich Brot“. Prinzipiell sind benötigte Leitungen fast immer zu kurz. 🙂 Also kommt hier ein kleiner Guide wie Ihr Leitungen schnell verbinden bzw. verlänger könnt.

Option 1: You have enough cable available

With this option, you have enough cable available and can strip approx. 2 cm of insulation from each end of the cable. This option is mechanically somewhat more stable and also easier to carry out than the following variant.

Option 2: You have little line available

Unfortunately, it is often the case that you do not have enough wire or cable available to strip 2 cm of insulation from each end. Especially in the event that a cable in a device is broken, there is often not enough cable available to connect the cable ends as described in option 1. Therefore, here is a possibility with which you can also connect very short cable ends.

Important rule when connecting cables:
The soldered area should always be larger than the cable cross-section to avoid excessive contact resistance.

Connect the solder pads to the breadboard:

Before the first prototype on a specially manufactured circuit board or for individual pieces, circuits are often built on breadboards. Perforated boards are printed circuit boards on which holes are arranged in a grid (hence the name :)). Often at a distance of 2.54mm which corresponds to 0.1inch. This is the quasi standard grid dimension for many components.

Das angenehme bei Lochrasterplatinen ist, dass auf der Unterseite der Leiterkarte(also der Kupferseite) sehr schnell Verbindungen zwischen Lötpunkten bzw. Bauteilen hergestellt werden können. Dazu wird im Prinzip eine „Lötzinn-Wurst“ über die zu verbindende Strecke gelegt.

How you can proceed is described in the following pictures.

Components with very large contact surfaces (e.g. XT60 connectors):

The disadvantage of soldering joints with very large metallic surfaces is that it takes a very long time to bring them to the desired temperature. In addition, the heat supplied is also dissipated very quickly. It can therefore take a very long time to heat these parts to the desired temperature. Sometimes it is not even possible because the metal (e.g. a large ground surface of a circuit board) emits heat over its large surface faster than it can be applied via the soldering iron.

As a small example, here are instructions on how to solder wires to XT60 connectors. These connectors are often used in model making. The great advantage of these is that they can transmit a continuous current of 60A, which is not uncommon, especially with larger multicopters. The disadvantage is that the solid plug contacts and the solid supply cables make it more difficult to connect the two together.

The difficult thing is that you cannot tin both contact surfaces individually and then solder them. This is because it usually takes a very long time to reheat the already tinned (and solid) contact of the XT60 plug and connect it to the connecting cable. The trick here is to heat the solid contact (in this case the XT60 connector), tin it and then only allow it to cool down once it has already been connected to the connecting cable.

First clamp the XT60 plug so that you have both hands free. A vice or a third hand is quite suitable for this.

Examples of good and bad solder joints:

Various solder joints on a THT component:

Below you can see a pin header where various mistakes were made when soldering the pins.

1.,2. and 4. were not soldered/forgotten at all
3. and 5. were only partially soldered. Solution: Heat again and add a little more solder
6. good solder joint
7. good solder joint
8. too little solder: solution: heat again and add some solder
9. too little solder and only partially soldered. Solution: Heat again and add solder
10. good solder joint, but a little more solder would not hurt
11. too much solder. Solution: Suck off/remove solder with a desoldering pump or soldering braid
12. cold solder joint. Solution: Heat again and add some solder if necessary

Bad solder joints on SMD components:

With SMD components in particular, where the contact surfaces are often located on the side and underside of the components, it is not always easy to see whether the components are properly soldered. Sometimes, however, a closer look is enough - if necessary with a magnifying glass, a microscope or a magnifying camera.

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Soldering SMD and THT components

You may have already noticed that there is a lot to write about soldering. And because the soldering of SMD and THT components differs again, both are described in the following separate articles.

Electronics – Solder SMD components by hand
Electronics – Solder THT components by hand

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Loosen/remove soldered components and clean contact points

Just as there are a few things to consider when soldering components to circuit boards, cables etc., there are also a few things to consider when desoldering and removing components that have already been soldered. A few things need to be taken into account, especially if you are cannibalizing old devices or still want to use the components. You can find information on this in the following article.

Electronics - Solder connections, clean and remove components

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Further information

https://www.computerwissen.de/hardware/pc-tipps/artikel/wichtige-massnahmen-zur-unfallverhuetung-beim-loeten.html

https://de.wikipedia.org/wiki/Lot_(Metall)

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Have fun with the project

I hope everything worked as described for you. If not or you have questions or suggestions please let me know in the comments. I will then add this to the article if necessary.
Ideas for new projects are always welcome. 🙂

PS Many of these projects - especially the hardware projects - cost a lot of time and money. Of course I do this because I enjoy it, but if you think it's cool that I share the information with you, I would be happy about a small donation to the coffee fund. 🙂