HowTo: Electronics – Solder SMD components by hand

After soldering THT components, soldering SMD components is the supreme discipline among the soldering challenges. The difficulty increases with the decreasing size of the components.

SMD stands for “Surface Mounted Devices” and is sometimes referred to as “SMT”, which means “Surface Mounted Technology”. Both terms refer to an assembly technique in which electronic components are soldered to the surface of the PCB. In contrast to THT components, SMD components are not inserted through the circuit board, but only placed on them and soldered in the correct position.

What sounds daunting at first is actually not. Of course, most SMD components are a bit smaller and the handling of tweezers also. Even a magnifying glass is sometimes necessary. But in addition, SMD components can sometimes be soldered even faster and easier than THT components. Easier and faster because there is no longer the annoying “insert component, fix component, turn over the circuit board, solder component …”-game that you may already know from THT components, needed. This will result in a “put on, solder, and finished”.game. So once you are skilled in “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 design of the circuit board.

So you can already tell: SMD technology offers several advantages. So that getting started is not that challenging, here are a few tips for soldering SMD components.

Hints for our lovely english readers: Basically, many of the articles on Nerdiy.de are translations from the original german articles. Therefore, it may happen here and there that some illustrations are not available in english and that some translations are weird/strange/full of mistakes or generally totaly wrong. So if you find some obvious (or also not obvious) mistakes don't hesitate to leave us a hint about that in the comment section. 
Also please don't get confused, that instead of a "dot" often a "comma" is used as decimal separator. 🙂


Safety instructions

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Requirements

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

Required material:

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

Tools required:

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


Size or housing shape of SMD components

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

ULN2003A in SO-16 housing

Information about the housing shape: https://en.wikipedia.org/wiki/Small_Outline_Integrated_Circuit

WS2812B in 5050 housing

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

Size Code (inch) according to the EIA standard length in mm width in mm length in inch width in inch
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

You can buy solder paste either filled 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 “stamp”, ie the part of the syringe with which the solder paste is pressed out of the syringe shell, is not always present. Therefore, when buying, pay attention to whether one already exists or has to be bought additionally. A small arsenal of tips is also helpful. Often there are no or only a few included.
An important information can also be read on the label: The solder paste is best stored at temperatures from 0 to 10 ° C. This information should be on every solder paste.
The label also contains information on the alloy from which the solder balls are composed and how large they are. In this case the alloy is: Sn63Pb37 and the size of the solder balls 25-45µm

Correct storage of solder paste:

The storage of the solder paste is a thing that makes the handling of solder paste a little more difficult than that of commercially available solder. While you can normal solder just leave it lying around, solder paste is a little more difficult. In contrast to solder, the flux contained in solder paste evaporates over time. This means that the solder paste will no longer appear as “liquid” over time and can therefore be applied more poorly. In addition, the solder contained in it then also bonds poorly to the respective metal surfaces.

This volatilization of the solder paste flux can be stopped. To do this, you must keep the solder paste at low temperatures – for example in the freezer. But make sure that you keep 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 definitely don’t want in your food!


SMD soldering with solder and soldering iron

The soldering of SMD components with solder and soldering iron actually always works on 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, at the same time attach the component and thus establish a first solder connection between the circuit board and the component.
3. Check whether the component has been correctly oriented / correctly polarized.
4. Solder the remaining contacts of the component.

Resistors/capacitors

Here, a capacitor is to be soldered in place “C7”.
To do this, some solder is first placed on the first pad with solder and a soldering iron. If you are right-handed, I always recommend starting with the right pad/pads on the right. So you can later feed the component from the left and hold the soldering iron with your right hand.
Now you lead the capacitor or component from the left side to the place to be soldered. Then briefly reheat the previously applied solder. The first contact surface of the capacitor should then be connected to the solder and the circuit board as shown.
Of course, this procedure works just as well with SMD resistors or all other components with two connection contacts. Here the resistor R5 has already been connected to the circuit board at a contact.
Now you only have to connect the second contact surface of the component with some solder to the circuit board.

Headers

To be added.

Post sockets

To be added.

ESP8266 ESP-12

The soldering of SMD components with several connection contacts is a bit more work but similar to the soldering of components with two contacts.
To do this, start again by applying some solder to a contact surface.
Then bring the component to the soldering point and solder it to the circuit board. Make sure that the component is aligned with the respective contact areas on the circuit board. At this point you still have the opportunity to correct this. To do this, simply heat the solder briefly again at the connection point and then fine-tune the component again.
If the component is then correctly aligned, you can connect the first row of contacts to the circuit board.
Then you can of course also connect the second row of contacts. The finished result should look something like this.

ICs

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

To do this, tin-plate one of the first contacts on the right or left side.
Then bring the component closer and align it with the contact surfaces.
As soon as the component is correctly aligned, you can also solder one of the other contacts (below left). This ensures that the component can no longer slip.
Then you can solder all contacts of the component to the underlying PCB.
Then check again that you have not created any short circuits/solder bridges between the contacts during soldering.

THT button

The soldering of THT pushbuttons – pushbuttons that are inserted through the circuit board – is described in the article Electronics – THT soldering components by hand.

SMD button

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

In this example, the SMD button is to be soldered at position “S1”.
Tin one of the contacts on the right side of the mounting surface again.
Then put the button on the PCB and make sure that it’s pins are aligned with the other solder pads..
“Aligned” means that the button or its contacts are all clearly within the contact areas on the PCB. This button could have been placed a little further to the left.
If the button is aligned, all remaining contacts can be soldered to the contacts on the PCB.

5050 LEDs

LEDs like 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 (with solder and a soldering iron) to the circuit board in this type of housing. Even an initially stable connection can easily break later by bending the circuit board or vibrations.

Therefore, you should better solder components in this type of housing with solder paste.


SMD soldering with solder paste and soldering iron

The procedure for soldering SMD components with solder paste and 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 whether 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 whether the component is still correct and aligned and oriented.
5. Solder the remaining contacts of the component according to the same scheme.

Resistors/capacitors

To be added.

Headers

To be added.

Post sockets

To be added.

ESP8266

To be added.

ICs

To be added.

THT button

The soldering of THT buttons is described in the section THT buttons in the article Electronics – THT component soldering by hand.

SMD button

In this example, the button on the mounting surface S4 is to be soldered to the circuit board.
Apply solder paste to all contact surfaces of the button.
Now you can put the button on the contact surfaces. If you are worried at this point that the solder paste could cause short circuits: rest easy. These connections pull apart again during the soldering process.
In the last step you only have to heat the contact surfaces and thus 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. Then the button can not slip. The solder gets hot and solders the button to the contact areas on the circuit board.

5050 LED’s

The procedure for soldering LEDs in the 5050 housing is similar again. In this example, an LED should be soldered to the “LED2” position.
Apply solder paste to the respective contact surfaces and …
… then solder the LED again by heating the contacts with the soldering iron.
When 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 in one go by hot air. Due to the resulting surface tension of the liquid solder, the respective component is then “automatically” pulled into the correct position. Components soldered in this way look very professional and save a lot of time, especially with larger 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 whether 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. Let the component and PCB cool down.

IMPORTANT: When soldering with hot air, it is important that you make sure that the components you soldered have not absorbed too much moisture beforehand. Otherwise it can happen that this moisture expands strongly during the heating and thereby “blows up” the housing, which would ultimately destroy the component. You can find out more about this problem in the following section “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 hot air or reflow processes, you should make sure that they are always packed airtight and in low moisture atmosphere.

Why is that 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 enclosed in such a way that it cannot escape again so quickly. If the component is now heated quickly during the soldering process, the stored moisture expands faster than it can escape from the component. This leads to the concerned components bursting open. That is why this phenomenon is colloquially called “popcorn”-effect.

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 air humidity is kept constant at a low level.

Of course, this is a little exaggerated for hobby use. Good results can also be achieved here by storing the components together with a few dehumidifier bags in a sealed plastic bag.

You can also see how sensitive to moisture the components you are using from the – mostly printed on the packaging – MSL value. This MSL (Moisture Sensitivity Level) indicates how long the respective components can be processed after opening the packaging without any damage being expected.

The MSL is divided into the following levels according to the current version of the J-STD-020D standard.

MSL-Level “Lifetime” after removal from the packaging
duration conditions
1 unbegrenzt 30 °C / 85 % RH
2 1 Jahr 30 °C / 60 % RH
2a 4 Wochen 30 °C / 60 % RH
3 168 Stunden 30 °C / 60 % RH
4 72 Stunden 30 °C / 60 % RH
5 48 Stunden 30 °C / 60 % RH
5a 24 Stunden 30 °C / 60 % RH
6 „time on label“
(TOL)
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 let these components dry in the drying cabinet for a certain time. As a home user, you can also let these components dry in a normal oven at 100 ° C for approx. 24 hours.

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

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


Which is not/very difficult to solder by hand

Unfortunately, not every component can be soldered in a controlled manner on the desk at home. For example, there are certain SMD housing forums such as BGA housings have their connection contacts on the underside of the component. This has the advantage that you can accommodate a lot of contacts 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 process. In addition, the solder joints cannot be checked or only with great difficulty. In production lines, printed circuit boards with BGA housings are checked after being fitted with an X-ray device. Unfortunately, most home users do not have this option.


Additional information

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

https://de.wikipedia.org/wiki/Moisture_Sensitivity_Level

http://www.netzmafia.de/skripten/hardware/SMD/index.html

https://makerfab.blogspot.com/2018/09/w-hy-ws2812sk6812-failures-after-smt.html

https://de.wikipedia.org/wiki/Chip-Bauform

https://de.wikipedia.org/wiki/Surface-mounted_device


I hope everything worked as described. If not or you have any other questions or suggestions, please let me know in the comments. Also, ideas for new projects are always welcome. 🙂

Fab

P.S. 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 appreciate it that I share these information with you, I would be happy about a small donation to the coffee box. 🙂

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4 comments

  1. Für mich als Einsteiger im Bereich smd bauteile löten ein sehr lesenswerter Ratgeber, vielen Dank.

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