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.
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/
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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.
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. the solder normally used contains a flux core. This is necessary/useful because it facilitates the bonding process of the solder with the metals of the respective contact surfaces. Sometimes, however, this can also cause the solder to "splatter", i.e. parts of it fly around uncontrollably. 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.
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.
Soldering iron vs. soldering station
The "soldering iron vs. soldering station" question cannot be answered in general terms. In most cases, a normal soldering iron will actually suffice. If you already have a soldering iron at home and only use it occasionally, for example to connect wires, you don't need to buy a new soldering station. Most of the advantages of soldering stations only become apparent when you use a soldering iron more regularly or want to use it for more specialized tasks.
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
As you can see, these are not "killer arguments" against the soldering iron. Only in the case that you want to solder components that have very critical temperature requirements can it become absolutely necessary to buy a soldering station with adjustable temperature. In most other cases, the soldering station is simply the more luxurious version of a soldering iron.
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.
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
Power of the soldering iron
In addition to the adjustable temperature range or the temperature of the soldering iron, the power is also a factor that should not be neglected. While the temperature indicates how hot the tip or the solder/solder pad/component/conductor (thermally) connected to it gets, the power (in the figurative sense) indicates how quickly this "heat" can be replenished.
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.
Duration of the soldering process
In short, a soldering process should always be as short as possible but as long as necessary.
You should therefore avoid "frying" components. If you are unsure what temperatures the component you are using can withstand, you can also take a look at the relevant data sheet. It lists the permitted temperatures with the respective operating times. If in doubt, simply allow the component to cool down a little between "soldering attempts" before starting the next attempt.
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 🙂
Solder/soldering tin what is useful, what is permitted and how much is necessary
Solder - also known colloquially as solder or solder wire - is basically "the glue" used to join two other metals together when soldering. Of course, the principle of soldering and gluing is completely different, but it illustrates quite well why solder is needed for soldering. Ideally, a good soldered joint results in two metal parts (e.g. two cable ends) being joined together in an electrically and thermally (sometimes also mechanically) stable manner.
The solder must first be heated so that it can fulfill its connecting task. To do this, it is important that the melting temperature of the two metals to be joined (e.g. two cable ends) is lower than that of the solder. This lower melting temperature is achieved by using a special mixture of different metals - also known as an alloy. The molten solder then flows into all the cracks between the metal parts and joins them together. This is where the name "solder" comes from, as many solder alloys often contain a large proportion of the metal tin.
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.
The composition of the solder is always indicated but unfortunately only somewhat "encrypted" readable. A few examples:
- 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.
A "very fine solder wire" would be a diameter of 0.3-0.5mm.
A "normal solder wire" would have a diameter of ~1mm.
Another important characteristic that you should consider when buying solder is that it must have a Flux core is provided. In principle, a solder wire is not a "wire" but a "tube", only on a very small and therefore poorly visible scale. The inside of this tube is filled with flux, which improves the flow properties of the solder. Without this flux - which often evaporates completely during soldering - the solder would flow much more poorly between the metals to be joined and bond with them. So always make sure that the solder you use also contains some flux.
The following is a close-up of the flux center core in a solder wire.
With the Quantity of solder there is a similar rule to the duration of the soldering process. In terms of quantity, "as much as necessary but as little as possible" also applies here. In production, attempts are made to keep the amount of solder used as low as possible, as this also keeps the costs as low as possible. Although this argument is not normally so critical for the home user, solder should still be used sparingly at home if possible. But how do you determine the perfect amount of solder?
This is best explained using a few examples and pictures. You can find these in the section "Examples of good and bad solder joints" below and in the articles Electronics – Solder SMD components by hand and Electronics – Solder THT components by hand.
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 🙂
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.
How it can be done more easily with "home remedies" is described below.
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.
If someone does need a "third hand" when soldering, I recommend the following. The big advantage of this one is that you can clamp it to the edge of the tabletop. This prevents the holder from falling over and provides a much better hold than the free-standing holders.
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.
Some components can cope well with this "thermal stress" (high temperature exposure), others less so. As a general rule, it is therefore advisable to keep the soldering process as short as possible but as long as necessary.
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.
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.
This is because solder and flux residues are quickly deposited by previous soldering processes, making heat transfer and sometimes even the view of the "operating area" more difficult.
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.
The second option consists of so-called "dry cleaners" which are very similar to metal rinsing sponges. With these, the soldering iron is simply dipped two or three times into the interwoven metal fibers until the tip is clean.
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.
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.
Almost any adhesive tape is suitable for this. However, if you want to play it safe, we recommend using "Kapton tape". This is temperature-resistant and can also be easily removed.
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.
General procedure during soldering
In the articles Electronics – Solder SMD components by hand and Electronics – Solder THT components by hand the soldering of THT (i.e. "through-hole") and SMD components is described in detail. In general, however, each soldering process can be divided into the following steps.
- Determine the maximum soldering temperature of all components involved in the soldering process and (if possible) set it on the soldering iron.
- Heat up the soldering iron and clean the tip.
- Prepare a suitable solder adapted to the size of the solder joint.
- 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.
- Apply some solder to the tip of the soldering iron. This facilitates the heat transfer from the tip later on.
- If possible, hold the tip of the soldering iron to both metal surfaces so that both are heated simultaneously.
- 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.
- Remove the soldering iron and allow the solder, component and circuit board to cool down.
Simple exercises and tips
Extend/connect cable:
Extending and connecting is the "bread and butter" of many DIY projects. In principle, the required cables are almost always too short 🙂 So here is a little guide on how you can quickly connect or extend cables.
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.
The nice thing about breadboards is that connections between solder points or components can be made very quickly on the underside of the PCB (i.e. the copper side). In principle, a "solder sausage" is placed over the section to be connected.
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.
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
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
Further information
https://de.wikipedia.org/wiki/Lot_(Metall)
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. 🙂
Great article detailing the importance of defect free solder joints when assembling PCBs. In addition, point 18 also mentions the reflow soldering of BGA components. With these special SMD components, the connections in the form of small solder balls are compact on the underside of the circuit board, in contrast to normal SMD components. These solder balls are melted using reflow soldering and thus connected to the contact pads on the printed circuit board.
Hey, thanks for the nice review. 🙂 Good point. I will add the details of the BGA components when I get a chance. I will post a first example that describes the typical structure of a circuit board with SMD components. 🙂
Hi, first of all thanks for the great instructions. A few hints will certainly help me with my next soldering actions. I have a question about soldering cables. As you show, it works for me sometimes 1A but...... then I have wires that I want to solder, where the solder is simply hanging on the soldering iron but just doesn't want to stick to the wire/wires. Sanding/cleaning the copper of the wires, putting soldering flux on it or even increasing the temperature to get the wire hotter has led to the fact that at some point even the insulation melts. But the solder just doesn't want to stick. Maybe you have a tip for me in such cases. By the way, I sometimes do that with components and circuit boards. If I previously soldered something out of there and then want to solder something else in that spot. What's wrong?
Thanks and regards
Stephen
Hi Stephen,
Thanks very much.
There are several reasons why some wires cannot be soldered together properly. Often it is because the copper of the lines is corroded. Sometimes it works if you apply some flux to the line. Flux can be purchased individually. This is simply applied to the area to be soldered and as soon as it is heated, it spreads over the solder joint. The solder should then stick better. 🙂
Best regards
Fabian