Sometimes PC technicians need to replace electronic components, such as electrolytic capacitors and connectors. The most common case is when you have a motherboard were the electrolytic capacitors leaked.
Desoldering and replacing components is not as easy as soldering them. The main problem is that printed circuit boards, especially motherboards, have several layers. You see only two layers (called “solder layer” and “component layer”), but there are other layers inside the printed circuit board, like a sandwich. The holes where the components are soldered to are metalized and serve not only to hold the component, but also to make the electrical connection between the two visible PCB layers and the internal PCB layers, which are not visible. If you make a wrong move while trying to remove a component, you may break the connection between the hole and the internal board layers, destroying your board.
In this tutorial we will explain you how to correctly desolder components, with several practical tips on how to get the best result.
To desolder components you will need the following tools:
- Soldering iron (25 W or 30 W, don’t use one above this power spec)
- Desolder pump (a.k.a. solder sucker)
- Cleaning cloth
- Cleaning sponge
- Small flat-tip screwdriver
- Isopropilic Alcohol (Isopropanol), do not use regular alcohol
Turn your soldering iron on and wait for it to get hot (three minutes, more or less). Wet the cleaning sponge and clean the soldering iron tip, making the movement shown in Figure 2. Make sure you repeat the movement until you have covered the entire tip. Some smoke will appear, don’t worry, that’s normal since the sponge is wet.
During the desoldering process you may need to clean the soldering iron tip again. Every time you see the soldering iron tip with black parts it is time to clean it again.
[nextpage title=”Locating the Component’s Terminals”]
The next step is to take a good look at the component you want to remove and locate its terminals. As we mentioned, a printed circuit board has two visible sides, the component side, where the components are located, and the solder side, where the components are soldered. So, we should locate the component on the component side and find its terminals on the solder side.
We will use as an example an electrolytic capacitor from a motherboard; we show it in Figure 3. So, we will need to locate its terminals on the solder side of the motherboard.
[nextpage title=”Cleaning The Terminals”]
First thing you need to do after finding the terminals of the component you want to desolder is to clean them with isopropilic alcohol (a.k.a. isopropanol) using a toothbrush. Just wet the toothbrush with isopropilic alcohol and brush the terminals. Do not use regular alcohol.
[nextpage title=”Preparing to Desolder”]
Now you will solder the component you want to remove. Yes, you read it right. You may be asking yourself why you should solder the component if you want to desolder it. Actually, this is a very powerful trick to allow old solder to be removed. What happens is that old solder (many years old) is very hard to be melted by the soldering iron and sucked by the solder sucker. So what you will do is to mix new solder with old solder. This mix is easier to melt and to be sucked.
There is another trick to be used during this process. With the soldering iron tip you should push the terminal back and forth in order to make it lose from the border of the hole. Many times the terminal is stuck at the border of the border, making it hard to be removed. You should repeat this process at least two times in each direction. After swinging the terminal with the soldering iron tip, you should leave the terminal more or less in the middle of the hole.
In the photos below we show these two tricks separately, but you should do the two things at the same time, also because swinging the component terminal helps to mix the old solder with the new one.
[nextpage title=”Desoldering the Component”]
To desolder the component you will need to use the solder sucker (solder pump). You should arm it by pushing its lever down. To use it, you should press its button, which is a trigger: its lever will get back to its normal position sucking everything located near its tip, hence its name. It works like if it was a small vacuum cleaner.
Here is the process: with one hand, you should melt the solder located at the component’s terminal, with the other, you should handle the solder sucker and aim its tip to the melted solder and press its button. The melted solder should be all gone.
Here is a tip: never keep your solder sucker armed after the job is done. This will make it to lose its pressure.
You also must pay attention to the correct way of handling the soldering iron, as we show in Figure 15. If you are left-handed you should invert the hands, of course.
[nextpage title=”Repeating the Process”]
It is very rare to suck all the solder at the first round (see Figure 17). You will need to repeat the process. You may need to solder the component again in order to mix new solder with the old one, facilitating the solder to be melted and sucked. Another tip is to move the terminal back and forth with a small flat-tip screwdriver, in order to lose the terminal from the hole.
Then you will need to repeat the process again until you see that the terminal is lose from the hole. In Figure 20, you can see both terminals at the end of the process. Pay attention on how the terminals are centered and there is no solder holding the terminals to the holes.
[nextpage title=”Removing the Component”]
To remove the component, just pull it with your fingers. If it is still stuck, there are some additional tips depending on the component.
If the component uses axial terminals (i.e., the terminals are in opposite sides of the component), you can hold the terminal on the component side of the board with a needle-nose pliers and pull it while, on the solder side of the board, touching the terminal with the soldering iron tip. This kind of component is rare in boards used in computers, however.
If the component uses radial terminals (i.e., the terminals are near at each other and placed on the same side of the component – like in the electrolytic capacitor we used as example), you may push it at one of its side with your thumb while touching the corresponding terminal with the soldering iron tip on the solder side of the board. For example, if you are pushing the capacitor left to right, you should heat the terminal located on the left. With electrolytic capacitors you can never use pliers to pull them off, because usually when you do that the capacitor will pop on your hand while its terminals will remain soldered. With components that have a “hard” surface – like transistors and integrated circuits – you may use pliers, if you think it will be useful.
For integrated circuits with DIP (Dual In Parallel) packaging, you can use a small flat-tip screwdriver to help you out. Just insert the screwdriver at one end of the integrated circuit (between the board and the component) and use it as a lever to lift the integrated circuit while heating the integrated circuit terminals on the same side as you put the screwdriver. Then do the same thing to the other side. Repeat that until you can fully remove the integrated circuit.
Beware. You can only follow those tips after performing all the standard procedure we described in this tutorial. If you try to pull a component without sucking its solder the way we explained, you may pull together with the component the metallic tube from the hole. This metallic tube is what makes contact between all the printed circuit board layers. If you do that, you will destroy the board, since the contact between the layers will be gone.
Pay attention to the polarity of the component you are removing, because you will need to match the polarity of the component you are going to install in the place of the component you’ve removed.
The desoldering process isn’t over yet. There is one final step. Keep reading.
[nextpage title=”The Final Touch”]
The final touch is cleaning the board. As you can see in Figure 24, after removing the component the board will have a brown resin all around the component holes. To remove this brown resin, use a small flat-tip screwdriver, as we show in Figure 25. Don’t push the screwdriver too hard or you will remove the board lacquer (green on the board we used in our example).
Now you need to clean the board with a toothbrush wet in isopropilic alcohol.
You should also clean the place the component was previously installed on the component side.
On Figures 29 and 30 you can see the final aspect of our motherboard.
Now the board is ready to get a new component in the place of the removed piece.