HowTo: Electronics – soldering SMD components by hand

After soldering THT components the soldering of SMD components is, so to speak, the supreme discipline among the soldering challenges. The difficulty increases as the size of the components decreases.

SMD stands for "Surface Mounted Devices" and is sometimes also referred to as "SMT", which means "Surface Mounted Technology". Both terms refer to an assembly technology in which electronic components are soldered to the surface of a printed circuit board for contacting. Unlike THT components, SMD components are not inserted through the PCB, but are simply placed on top of it and soldered in the correct position.

What sounds daunting at first is actually not. Of course, most SMD components are somewhat smaller and require the use of tweezers and possibly even a magnifying glass, but beyond that, these components can sometimes be soldered faster and easier than THT components.

This eliminates the annoying "insert component, fix component, turn PCB over, solder component..." game that you may already know from THT components knows. It quickly becomes a "put on the component, solder it and you're done" game. Once you have practiced "SMD soldering", you save a lot of time. In addition, many components are now only available in SMD form. This also saves space in the PCB design.

As you can already see, SMD technology offers a number of advantages. Here are a few tips on soldering SMD components so that getting started is not quite so challenging.

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.

Affiliate links/advertising links

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Helpful articles:
You can find more helpful information on the basics of soldering in the following article:
Electronics - My friend the soldering iron
Electronics - Solder connections, clean and remove components

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.

Size and housing shapes of SMD components

Not all housing shapes are shown in the following article. Only the most common

ULN2003A in SO-16 housing

Information on the housing shape:

WS2812B in 5050 housing

Information on the housing shape can always be found in the data sheet of the respective component. In this case, however, the name already indicates the dimensions: the first 50 in the name means that the first edge of the housing is 5.0 mm long. The second 50 analogously means that the second side of the housing is 5.0 mm long.

Code (inch) according to EIA standard
Length in mm Width in mm Length in inches Width in inches
01005 0,4 0,2 0.016 ± 0.0008 0.008 ± 0.0008
0201 0,6 0,3 0.024 ± 0.002 0.012 ± 0.001
0402 1.02 ± 0.10 0.50 ± 0.10 0.040 ± 0.004 0.020 ± 0.004
0504 1.27±0.15 1.02 ± 0.15 0.050 ± 0.006 0.040 ± 0.004
0603 1.60 ± 0.10 0.80 ± 0.10 0.063 ± 0.004 0.031 ± 0.004
0805 2.00 ± 0.15 1.25 ± 0.15 0.079 ± 0.006 0.050 ± 0.006
0907 2.29 ± 0.20 1.78 ± 0.20 0.090 ± 0.008 0.070 ± 0.008
1008 2.50 ± 0.15 2.00 ± 0.15 0.098 ± 0.006 0.078 ± 0.006
1206 3.20 ± 0.15 1.60 ± 0.15 0.126 ± 0.006 0.063 ± 0.006
1210 3.20 ± 0.15 2.50 ± 0.15 0.126 ± 0.006 0.098 ± 0.006
1411 3.50 ± 0.20 2.80 ± 0.20 0.138 ± 0.008 0.110 ± 0.008
1515 3.81±0.38 3.81±0.38 0.150 ± 0.015 0.150 ± 0.015
1608 4.00 ± 0.20 2.00 ± 0.20 0.157 ± 0.008 0.078 ± 0.008
1812 4.60 ± 0.20 3.20 ± 0.20 0.181 ± 0.008 0.126 ± 0.008
1825 4.60 ± 0.20 6.30 ± 0.20 0.181 ± 0.008 0.248 ± 0.008
2010 5.08 ± 0.13 2.54 ± 0.08 0.200 ± 0.005 0.100 ± 0.003
2220 5.70 ± 0.20 5.00 ± 0.20 0.224 ± 0.008 0.197 ± 0.008
2312 6.00 ± 0.20 3.20 ± 0.20 0.236 ± 0.008 0.126 ± 0.008
2512 6.35 ± 0.13 3.20 ± 0.08 0.250 ± 0.005 0.126 ± 0.003
2515 6.30 ± 0.20 3.81 ± 0.20 0.248 ± 0.008 0.150 ± 0.008
2716 7.00 ± 0.20 4.00 ± 0.20 0.275 ± 0.008 0.157 ± 0.008
2824 7.20 ± 0.20 6.10 ± 0.20 0.283 ± 0.008 0.240 ± 0.008
2917 7.30 ± 0.20 4.30 ± 0.20 0.287 ± 0.008 0.170 ± 0.008
2920 7.30 ± 0.20 5.00 ± 0.30 0.287 ± 0.008 0.197 ± 0.012
3111 8.00 ± 0.20 2.80 ± 0.20 0.315 ± 0.008 0.110 ± 0.008
3931 10.00 ± 0.20 8.00 ± 0.20 0.394 ± 0.008 0.315 ± 0.008
4018 10.16 ± 0.20 4.60 ± 0.20 0.400 ± 0.008 0.181 ± 0.008
4040 10.2 ± 0.50 10.2 ± 0.50 0.400 ± 0.020 0.400 ± 0.020
4320 11.00 ± 0.20 5.00 ± 0.20 0.433 ± 0.008 0.197 ± 0.008
4335 11.00 ± 0.20 9.00 ± 0.20 0.433 ± 0.008 0.352 ± 0.008
4349 11.00 ± 0.20 12.50 ± 0.20 0.433 ± 0.008 0.492 ± 0.008
4424 11.10 ± 0.81 6.10 ± 0.40 0.435 ± 0.032 0.240 ± 0.015
4527 11.50 ± 0.20 7.00 ± 0.20 0.455 ± 0.008 0.275 ± 0.008
4540 11.4±0.58 10.2 ± 0.50 0.450 ± 0.023 0.400 ± 0.020
4723 12.00 ± 0.20 6.00 ± 0.20 0.472 ± 0.008 0.236 ± 0.008
4825 12.20 ± 0.20 6.35 ± 0.20 0.480 ± 0.008 0.250 ± 0.008
5550 14.00 ± 0.71 12.70 ± 0.63 0.550 ± 0.028 0.500 ± 0.025
5727 14.40 ± 0.20 7.00 ± 0.20 0.567 ± 0.008 0.275 ± 0.008
6145 15.50 ± 0.20 11.50 ± 0.20 0.610 ± 0.008 0.455 ± 0.008
6561 16.50 ± 0.20 15.50 ± 0.20 0.651 ± 0.008 0.610 ± 0.008
7565 19.10 ± 0.96 16.50 ± 0.83 0.750 ± 0.038 0.650 ± 0.033

Solder paste

Solder paste can either be bought in a syringe or in a normal container with a screw cap. The advantage of the syringe is that you can apply the solder paste directly to the required solder pads.
The "plunger", i.e. the part of the syringe with which the solder paste is pressed out of the syringe barrel, is not always present. Therefore, when buying, check whether one is already included or whether you need to buy an additional one. A small arsenal of tips is also helpful. Often the soldering paste does not come with any or only a few.
There is also important information on the label: The solder paste is best stored at temperatures between 0 and 10°C. This information should be on every solder paste.
The label also contains information on which alloy the solder balls are made of and how big they are. In this case the alloy is: Sn63Pb37 and the size of the solder balls is 25-45µm

Correct storage of solder paste:

The storage of solder paste is one thing that makes the handling of solder paste a little more difficult than that of commercially available solder. While you can simply leave solder lying around, this is somewhat more difficult with solder paste. In contrast to solder, the flux contained in solder paste evaporates over time. This means that the solder paste no longer appears as "liquid" over time and is therefore more difficult to apply. In addition, the solder it contains also bonds less well with the respective metal surfaces.

However, this evaporation of the solder paste flux can be stopped. To do this, you must store the solder paste at low temperatures - for example in the freezer. However, make sure that you store the solder paste either separately from food or very well packaged in the freezer. Remember that solder paste often contains lead and other substances that you do not want in your food! 

SMD soldering with solder and soldering iron

Soldering SMD components with solder and a soldering iron always follows the same principle.

1. tin a free solder pad - preferably one that is not connected to a large copper surface - with a little solder.
2. heat the solder on the tinned pad, place the component on it at the same time and thus create an initial solder connection between the PCB and the component.
3. check whether the component has been correctly oriented/polarized.
4 Solder the remaining contacts of the component.


A capacitor is to be soldered to position "C7" here.
To do this, first apply some solder to the first pad using solder and a soldering iron. If you are right-handed, I recommend that you always start with the right-hand pad(s) on the right-hand side. This way you can later feed the component from the left and hold the soldering iron with your right hand.
Now bring the capacitor or component from the left-hand side up to the point to be soldered. Then briefly heat the previously applied solder again. The first contact surface of the capacitor should then be connected to the solder and the circuit board as shown.
Of course, this procedure also works with SMD resistors or all other components with two connection contacts. In this case, resistor R5 has already been connected to the PCB at one contact.
Now all you have to do is connect the second contact surface of the component to the circuit board with a little solder.

Pin headers

To be added.

Post bushes

To be added.

ESP8266 ESP-12

Soldering SMD components with multiple contacts is a little more work but similar to soldering components with two contacts.
Start again by applying some solder to a contact surface.
Then bring the component up to the soldering point and solder it to the circuit board. Make sure that the component is aligned congruently with the respective contact surfaces on the circuit board. You still have the option of correcting this at this point. To do this, simply heat the solder again briefly at the connection point and you can then finely align the component again.
If the component is then correctly aligned, you can connect the first row of contacts to the circuit board.
You can then of course also connect the second row of contacts. The finished result should look something like this.


The soldering of ICs in the SOP housing also works according to a similar principle.

Tin one of the first contacts on the right or left side again.
Then approach the component and align it with the contact surfaces.
As soon as the component is correctly aligned, you can also solder one of the other contacts (bottom left here). This ensures that the component can no longer slip out of place.
You can then solder all the contacts of the component to the underlying contacts on the circuit board.
Then check again that you have not created any short circuits/solder bridges between the contacts during soldering.

THT push-button

The soldering of THT push-buttons - i.e. push-buttons that are inserted through the circuit board - is described in the article Electronics – Solder THT components by hand described.

SMD push-button

SMD buttons can also be easily soldered using solder and a soldering iron.

In this example, the SMD button is to be soldered to position "S1".
Tin one of the contacts on the right-hand side of the mounting surface again.
Then put on the push-button and make sure that it is aligned straight.
"Aligned straight" means that the button or its contacts are all clearly within the contact surfaces on the PCB. This button could even have been placed a little further to the left.
Once the button is aligned, all remaining contacts can be soldered to the contacts on the PCB.

5050 LEDs

LEDs such as the "famous" WS2812B also have contacts that are reasonably accessible from the outside. However, the majority of these contacts are located on the underside of the LED housing. For this reason, these LEDs cannot be reliably soldered to the circuit board in this type of housing. Even an initially stable connection can easily break later due to bending of the circuit board or vibrations.

It is therefore better to solder components in this type of housing with soldering paste.

SMD soldering with solder paste and soldering iron

The procedure for soldering SMD components with solder paste and a soldering iron is almost always similar and can be summarized as follows.

1 Coat all solder pads of the desired component with solder paste.
2. position the component, align it correctly and check that it is correctly oriented.
3. without touching the component leg (this could cause the component to slip), heat the solder pad of the first component leg until the solder paste liquefies and the component leg is soldered to the solder pad
4. check again that the component is still correctly aligned and oriented.
5. solder the remaining contacts of the component according to the same pattern.


To be added.

Pin headers

To be added.

Post bushes

To be added.


To be added.


To be added.

THT push-button

The soldering of THT push-buttons is described in section THT push-button in the article Electronics – Solder THT components by hand described.

SMD push-button

In this example, the push-button is to be soldered to the PCB on mounting surface S4.
Apply solder paste to all contact surfaces of the button.
Now you can place the button on the contact surfaces. If you are worried at this point that the solder paste could cause short circuits: Don't worry. During the soldering process, these connections will pull apart again.
The last step is to heat the contact surfaces and solder the button to the circuit board. To do this, carefully guide the soldering iron to the contact surface without touching the leg of the button. This prevents the button from slipping. The solder becomes hot and solders the button to the contact surfaces on the circuit board.

5050 LEDs

To solder LEDs in the 5050 housing, proceed in a similar way. In this example, an LED is to be soldered to the "LED2" position.
Apply solder paste to the respective contact surfaces again and...
...then solder the LED again by heating the contacts with a soldering iron.
Once soldered, the whole thing should look something like this.

SMD soldering with solder paste and hot air station

Soldering with solder paste and hot air is really fun once you know how to do it. The big advantage is that you only have to apply the solder paste and roughly insert the component into it. The component, the solder paste and the circuit board/solder pads are then heated by hot air in "one go". The resulting surface tension of the liquid solder then "automatically" pulls the respective component into the correct position. Components soldered in this way look very professional and save a lot of time, especially with large numbers of components.

The procedure for soldering with solder paste and hot air can be roughly divided into the following steps.

1 Coat all solder pads of the desired component with solder paste.
2. position the component, align it correctly and check that it is correctly oriented.
3. heat the component, solder paste and circuit board with hot air to the melting temperature of the solder paste until the component "floats" completely.
4. allow the component and circuit board to cool down.

IMPORTANT: When soldering with hot air, it is important that you make sure that the components you are soldering have not absorbed any or too much moisture beforehand. Otherwise, this moisture may expand considerably during heating and "burst" the housing, which would ultimately destroy the component. You can find out more about this problem in the following paragraph "Storage of SMD components".

SMD soldering with solder paste and oven (reflow soldering)

SMD soldering with solder paste and an oven is almost identical to soldering with hot air. The only difference is that this time the heat does not come from the hairdryer of the hot air station but from an oven. To be precise, the circuit board fitted with solder paste and components is placed in the oven. The oven then follows a programmable temperature curve in which the components and circuit board are first preheated and then soldered.

This process is also known as reflow soldering and is basically the same soldering process that is used in professional manufacturing processes. Then, of course, on a somewhat larger scale and highly automated.

The procedure can be divided into the following steps.

1 Coat all solder pads of the desired component with solder paste.
2. position the component, align it correctly and check that it is correctly oriented.
3. place the fully (or partially) assembled PCB in the oven and start the soldering process.
4 Remove the circuit board from the oven and allow to cool.

IMPORTANT: It is also important when reflow soldering that you ensure that the components you are soldering have not absorbed any or too much moisture beforehand. Otherwise, this moisture may expand considerably during heating and "burst" the housing, which would ultimately destroy the component. You can find out more about this problem in the following paragraph "Storage of SMD components".

Storage of SMD components or how to prevent the popcorn effect

If you want to solder SMD components now or in the future using the hot air or reflow method, you should make absolutely sure that they are always packaged airtight and with low moisture content.

Why is this a problem?
Unfortunately, SMD components and the plastic used for them absorb moisture very easily. The moisture contained in the normal ambient air is sufficient for this. This is absorbed by the plastic of the SMD components and trapped in such a way that it cannot escape again so quickly. If the component is now heated quickly during the soldering process, the trapped moisture expands faster than it can escape from the component. This causes the affected components to burst open. This is why this phenomenon is also known colloquially as "Popcorn" effect called.

To prevent this error, it is important that you always store your SMD components in a dry and airtight place. In professional use, there are special drying cabinets for this purpose, in which the humidity is constantly kept at a low level.

This is of course a little excessive for hobby use. However, good results can also be achieved here by storing the components together with a few dehumidifier sachets in a sealed plastic bag.

You can also tell how sensitive the components you are using are to moisture by the MSL value, which is usually printed on the packaging. This MSL (Moisture Sensitivity Level) indicates how long the respective components can be processed after opening the packaging without damage being expected.

The MSL is divided into the following levels in accordance with the current version of the J-STD-020D standard.

MSL level "Lifetime" after removal from the packaging
Duration Conditions
1 unlimited 30°C / 85 % RH
2 1 year 30°C / 60 % RH
2a 4 weeks 30°C / 60 % RH
3 168 hours 30°C / 60 % RH
4 72 hours 30°C / 60 % RH
5 48 hours 30°C / 60 % RH
5a 24 hours 30°C / 60 % RH
6 "time on label"
30°C / 60 % RH

How do you get components that have become "damp" dry again?

In the event that the "child has already fallen into the well" and your SMD components with MSL-6 have been flying around openly on your desk for weeks, there is still some hope. In professional use, you would now leave these components to dry in the drying cabinet for a certain period of time. As a home user, however, you can also dry these components in a normal Dry in the oven at 100°C for approx. 24 hours leave.

This will cost you some energy costs but can be cheaper than having to order the components again.

IMPORTANT: Make sure you place at least one base in your oven. The components could be contaminated with harmful materials, which should not necessarily end up on your favorite baking tray. If you want to be on the safe side, you can also get a pizza oven and use it exclusively as a drying oven.

What cannot/is very difficult to solder by hand

Unfortunately, not every component can be soldered in a controlled manner on your desk at home. For example, there are certain SMD housing forums, such as BGA housings, whose connection contacts are on the underside of the component. This has the advantage that a large number of contacts can be accommodated in a relatively small space.

Unfortunately, this also has one and a half major disadvantages for home users: these components cannot be soldered with a soldering iron, but only with hot air or using the reflow method. In addition, the solder joints are very difficult or impossible to inspect. In production lines, PCBs fitted with BGA housings are checked with an X-ray machine after assembly. Unfortunately, most home users do not have this option.

Further information

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. 🙂

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  1. For me as a beginner in the field of soldering smd components, this is a guide worth reading, thank you very much.

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