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How To Desolder – The Correct Process For Reworking PCBs
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May 26, 2023
Soldering
Desoldering is a fundamental skill that everyone working with electronic devices must master.
If you aren’t sure where you need to start, our guide has you covered.
In this article we will explore how to desolder, the equipment you require and common mistakes that occur, taking into account desoldering for both through hole and surface mount components.
| Article Contents | |
| What Is Desoldering? | |
| Equipment Needed | |
| Desoldering Process: | |
| 1 – Preparation | |
| 2 – Heat Application | |
| 3 – Remove Component & Solder | |
| 4 – Cleaning The Joint | |
| 5 – Repeat The Process (If Needed) |
What Is Desoldering?
Desoldering is the process by which you remove soldered components or soldered connections from a PCB or device.
Heat is applied to the solder joint causing the solder to melt and become fluid once more. This solder is then pulled away from the PCB, freeing the component.
There are 2 main ways in which you can desolder. One is by using a soldering iron, and the other is by using a hot air station. The method you select will be determined by the type of component you are looking to desolder, such as through hole or SMT.
The differences between the two can be outlined as follows:
Heat Source – The primary difference between these two desoldering methods is the heat source. Desoldering through the use of a soldering iron applies the heat through direct contact between the soldering tip and the solder you wish to remove. Hot air uses a direct stream of heated air to melt the solder the PCB.
Component Type & Size – For larger components and SMT components, the typical desoldering method is through hot air. Soldering irons are more appropriate for smaller or through-hole components.
Precision – When desoldering through a soldering iron, you can better manipulate and remove solder from specific areas, when compared to hot air. More precautions need to be taken when desoldering through hot air, to ensure the protection of surrounding components.
Equipment Required To Desolder
Desoldering will require a specific set of equipment to ensure a successful process. Below is the type of equipment you will require:
Method For Solder Heating
For all rework applications, you need a means of providing heat to the solder joint, in order to turn the solder into a molten state.
This is primarily achieved through one of 2 ways – direct heat contact, or hot air.
Direct contact is achieved through the use of a soldering iron. The joint is reheated by touching the hot iron onto the solder on the joint, making it flow once more and releasing its grip on the component you are desoldering. You can achieve these results with a standard soldering iron, specialised desoldering tool or even rework tweezers. Which you use will often depend on the board and components you work with.
Hot air rework involves a concentration of heated air, directed at the solder joint. You would need a hot air station for this work, along with other handy accessories that can help to better direct and concentrate the blast of heat.
We will delve a little deeper into when each method should be used a bit further down!
Method For Solder Extraction
Once the solder has been heated and begins to flow, you will then need to extract it from the PCB. There are 2 main ways that this is done, outlined below:
Desoldering Pump – This is a tool that acts as a vacuum, extracting the melted solder out of the joint. The solder will need to be heated up before the pump can be used. If the desoldering pump is not attached to the soldering iron (like some JBC desoldering irons are) then you will need to ensure that you act quickly with the pump, once the solder has been heated up. This prevents the solder from cooling down and hardening up once more.
Desoldering Braid – This is a coiled up length of copper wire that has often been coated with a flux. This works to absorb the melted solder from your board. You may also know this as a solder wick. It works due to copper being an excellent conductor of heat, and as we know, solder will flow towards the heat. If your braid is not coated with flux, then you can simply apply a liquid flux to the braid before using.
Fluxing Agent
A fluxing agent is crucial to the desoldering process, as it helps to clean and prepare the solder joint for removal.
When the solder joint is heated, the flux will activate and help to clean the surface of the joint. This allows the solder to flow more easily, thus making it easier to remove.
Additionally, the flux will aid in cleaning the joint, preventing oxidation during the desoldering process.
Make sure that you use the right type and amount of flux for your specific application for the best results.
Cleaning Method
Cleaning equipment is essential for reworking solder joints, just as it is for the soldering process. It is essential that any remaining solder or flux residue is removed from the PCB. This can include the following:
- Clean cloths or cotton swabs
- Isopropyl alcohol or another PCB cleaner
Standard Soldering PPE
It is always recommended that you wear the appropriate soldering PPE each time you desolder. As with any soldering application, rework tasks similarly work at high temperatures, involving hot molten solder.
This can easily cause injury if you are not fully protected.
Similarly, ensure that sufficient fume extraction is in place to remove the solder fumes that will be generated from the desoldering process.
You should also ensure that the correct static control precautions are being followed if you are working with static-sensitive devices.
Ensure that you have at minimum the following:
- Safety glasses & Heat resistant gloves – Help to protect your eyes from solder splatters.
- Heat-resistant mat – Helps to protect your work surface from being damaged.
- Fume Extraction – To remove solder fumes
- ESD Control – This includes wrist straps, grounding cords and more.
So, What Is The Desoldering Process?
Desoldering is a crucial process for rework and repair operations within electronics. Whether it’s required to repair a faulty circuit or to salvage components from the PCB, it is a skill that must be mastered and conducted correctly.
Below we have outlined the desoldering best practices that must be adhered to for the best results:
Step 1 – Preparation
Whether you are desoldering through hot air, or soldering iron, the preparation will be the same.
Firstly, it is imperative that you have the required equipment close to hand before starting the desoldering process. This minimises any possible delay and stops you from needing to reapply heat should you not have the solder braid or pump to hand just when you need it.
Just as important is the working area in which you are conducting the rework application in. Make sure you adhere to correct housekeeping practices, such as a clean work surface, minimal clutter, good ventilation/LEV extraction and no obstructions to your view that could affect your ability to see the component.
Step 2 – Heat Application
As mentioned above, there are 2 primary ways that heat will be applied for the desoldering process. That is through direct contact with a soldering iron, or from a hot air station.
Whichever method you are using, apply the heat to the solder joint that you intend to desolder. Either apply a concentrated blast from the hot air station onto the component or heat up your soldering iron and place it on the joint until the solder begins to flow.
Make sure that you also apply a small amount of flux to the solder joint and the solder will melt quickly.
The method that you decide to use may depend on the types of components that you are working with. Through hole, components are on the whole larger, and therefore the operator may prefer to target the individual pins with a soldering iron for precise rework.
SMT components, however, are smaller and with multiple leads, meaning that hot air targeting is much more efficient for the task.
It is crucial that you use the appropriate desoldering method for the type and size of component that you are working with.
Step 3 – Remove Component & Solder From The PCB
Now that the heat has been applied the component can be removed from the PCB using your tweezers or any extractors for certain SMD components.
As the solder is now in a flowing state, it is time to remove this from the PCB using either a solder wick or a desoldering pump. Primarily this is done using one of two methods:
Desoldering Pump – The desoldering pump will hoover up the molten solder from the PCB and store it for disposal. Simply place the pump over the top of the solder joint and activate the vacuum to draw away the solder.
Desoldering Braid – These work pretty similarly also. Place the wick over the joint you plan to desolder and apply heat so that the solder joint becomes molten. As the solder melts, the flux in the desoldering braid will activate and draw the molten solder up through the braid and away from the solder joint. Once complete, carefully remove it from the joint.
Both methods are effective means of extracting unwanted solder from a PCB. Which method you use will depend on the specific application.
A solder wick would be more suited for smaller and more delicate solder joints. However, larger joints or those that present access issues are likely better suited to using a desoldering pump.
Once the solder is gone, the component can be lifted from the board with tweezers.
Step 4 – Cleaning The Joint
Next, you will need to clean the solder joint.
An integral part of the desoldering process is also cleaning.
Once the solder has been removed, use a clean cloth or a cotton swab to clean the joint thoroughly and carefully. Make sure that all residual solder or flux is removed from the joint.
You can also use PCB cleaning products or other isopropyl alcohol solutions to provide the joint with a further clean.
It is also important that you re-tin your soldering iron before replacing it into the stand, should that be the equipment you are using. Standard tip care practices are important here as they are with other soldering applications.
Step 5 – Repeat The Process (As Required)
Depending on how many components require desoldering work, you can repeat the above process as many times as is required.
You must make sure to repeat the above process for each joint that you are intending to desolder.
If you are desoldering with a soldering iron, ensure that you clean the tip regularly in between the desoldering of each joint. This way you ensure that your equipment works efficiently throughout the entire process.
In Summary
Hopefully, this guide has shed some light on the best way to conduct your desoldering applications.
Each application often requires a different approach, so before desoldering, ensure that you evaluate the PCB and components that you are working with. This way you can always select the best equipment and means to achieve the best results from your rework process.
For help sourcing or selecting any rework equipment, feel free to get in touch with our team!
-
The Top Mistakes When Desoldering & How To Prevent Them