Contents
Understanding Desoldering and Solder Removal
Desoldering and tools
What is Desoldering?
Desoldering involves removing bad, inefficient, or unwanted solder on a PCB. Removal occurs by using a special tool to melt the solder on the component leads or pads. This allows you to repair issues, such as solder bridges or poor connections. Technicians also use it for removing and replacing failed components while keeping the PCB intact.
Desoldering is convenient for changing a component’s position on the PCB. Some examples include functionality upgrades, design improvements, freeing space, error correction, and boosting performance.
Common Tools for Desoldering
Desoldering Pump:
The desoldering pump (solder sucker) sucks up molten solder on the board. Use the pump when necessary for solder bridges and component replacement. This tool is preferred for through-hole components, large solder joints, and quickly removing solder. However, it’s ineffective for smaller joints or surface-mount devices (SMDs).
Desoldering Braid/Wick:
Technicians use the desoldering braid—an excellent tool for solder removal and repair. It has copper wire braids that absorb solder after it has melted from the heat applied by a soldering iron.
This is precise as it removes solder in hard-to-reach areas like small joints and tightly packed components. It’s also safer for components due to the short-term heat application. Users can select different widths and flux types for various applications and sizes.
Other Tools:
A desoldering bulb produces suction after squeezing the rubber bulb. It collects the molten solder upon release. All-in-one solutions are a combination of a desoldering tool and a soldering iron. You can get them with either a desoldering bulb or a plunger.
Step-by-Step Guide to Using a Desoldering Pump
Desoldering pumps are very easy to use and require minimal effort. Here’s how you can remove solder with this tool.
Preparation
Clean the workstation. Use a microfiber cloth or compressed air to remove on-surface contaminants. The work area must have excellent lighting so you can see clearly while desoldering.
De-clutter the surface, placing tools and parts into trays or containers for organization. This gives you proper access to the soldering iron, goggles, gloves, and desoldering pump.
Plug in the soldering iron and let it heat up to temperatures ranging from 300°C to 350°C—depending on solder type. Once the iron has heated, put some solder on the tip for better heat transfer and protection. Apply the soldering iron to the preferred solder joint, holding it in place until it melts into molten.
Using the Pump
Before placing the pump over the molten solder, fully compress the plunger until it locks. Afterward, position the desoldering pump directly above the melted solder. Release the plunger by pushing the button. This will produce a suction that sucks up the molten solder, placing it in the pump.
Post-Desoldering
Lastly, you will need to inspect the work area to determine if the joint has been desoldered. If there’s still some leftover, repeat the steps until there’s no more solder. Remove the molten solder from the pump’s chamber to clean it by detaching the nozzle and pressing the plunger down.
Advantages and Disadvantages of Using a Desoldering Pump
A desoldering pump can be used again—even after removing solder, a cost-effective solution. If needed, it removes plenty of solder from through-hole component joints quickly and efficiently. It’s also designed for small areas and microscopic openings.
However, it’s inefficient for smaller areas with tight spaces in which surface-mounted components integrate. There’s also a risk of damage to components due to the suction power.
Cold Solder Joints: How to Detect and Repair?
Cold solder joint repair
It’s important to watch out for solder issues that may form, including cold solder joints. They can interfere with circuit functionality and lead to other problems. Repairing it when possible will help salvage the component and PCB.
What is a Cold Solder Joint?
A cold solder joint is a solder joint in which the solder fails to melt entirely. This happens when the solder wire improperly heats before soldering. In some cases, it can also emerge when one disturbs the board or the soldered pin before the molten solder solidifies.
Detection Methods
Visual inspection
You should check for and repair cold solder joints after circuit development. A cold solder joint looks dull and makes convex mounting on the pins and the board flex areas. Sometimes, they also form rough shapes.
Get a magnifying lens to check through the solder joints to note the convex shape and ensure the solder fills the gaps. Light shouldn’t pass through the joints. You can also use the lens to find joints that didn’t have sufficient heat applied to the solder. Those joints appear rough upon close inspection.
If you’re skeptical of a joint problem, tilt the component mounted on the joint to see if it detaches.
Multimeter
Switch the multimeter to measure resistance—indicated by the Ohm (Ω) symbol. Rotate the indicator or press the control dials to switch. Use a 1K ohms resistance for this measurement.
Connect one multimeter terminal to the other meter terminal. A 0 Ohms resistance means the multimeter functions correctly. Afterward, connect the meter’s terminal to a joint on one end and the other on a different end through a component. A zero should appear for non-resistor components. Readings higher than zero are indicative of a cold joint.
Switch the multimeter measure to gauge continuity. Connect both ends of the multimeter, which beeps to indicate continuity. Connect two ends of the multimeter to both ends of the circuit. If the multimeter beeps, everything looks good. Anything else indicates discontinuity due to a cold solder joint.
Repairing Cold Solder Joints
Repairing a cold solder joint is pretty straightforward. Grab the soldering iron, set the appropriate temperature, and apply heat to the cold solder joint. Add fresh solder as it heats—this will create a solid bond.
Ensure the component and pad are properly heated so the solder flows naturally. You’ll also need to keep the joint stabilized as it hardens. This keeps it from detaching from the component lead.
Preventing Cold Solder Joints
Set the soldering iron to an optimal temperature to achieve smooth, uniform solder flow.
Don’t use too much heat, as it can damage the components. Sudden movements can produce a weak bond or cold joint.
You can also achieve strong connections by using fresh, high-quality solder with the best flux.
How to Remove Solder from Circuit Boards?
There are numerous ways to desolder your circuit board—ranging from machine-powered tools to manual.
Most DIY projects require a desoldering pump and braid. But the choice usually comes down to personal preference.
Methods for Surface-Mounted Components
Grinding and Scraping:
Grinding and scraping are useful for precise work on fragile areas of a PCB.
It’s also used for cleaning after the desolder process. Grab a pick, sharp knife, or scraper, and apply slight pressure on the excess solder or solder mask.
This approach will remove it without damaging the components or circuit.
Chemical Stripping:
This technique uses a liquid chemical solvent applied with a brush or swab. It’s best to use it to remove solder on copper plates or solder surfaces.
Add masking tape or other protective material to safeguard the PCB. The solvent breaks down the solder but deteriorates the base material if you allow it.
Microblasting:
Microblasting the PCB is best for removing solder from a large surface area.
Small bench-top systems propel abrasive materials at the target through a pencil-shaped handpiece, which must be flushed away after application.
This abrasive material blasts away the coating.
Removing Solder from Through-Hole Components
Drilling:
A drill can remove solder from the clogged PCB holes if a braid or bulb fails to get the job done. Since many holes are 0.029 inches in diameter, use a small enough carbon, cobalt, or high-speed steel bit.
Oversized bits will remove the tracing within the hole, damaging the board.
Go slow, as quick drilling may damage the circuit traces or layers. Applying too much pressure can cause you to drill through the circuit, making it inoperable.
Using Desoldering Braid:
Before getting started, heat the solder iron and place the braid over the old solder joint—covering it completely.
Heat the braid by placing the solder iron tip on top of it, which will liquify the solder.
This causes the braid to absorb the melted solder. Remove the braid and iron simultaneously and look over the joint to ensure there’s no solder left.
Repeat the steps if you still see solder on the joint.
All-in-One Solutions:
An all-in-one desoldering unit is even better as it melts the solder and vacuums it simultaneously. This slashes the time needed for repair and rework.
For added convenience, users can adjust the temperature and suction power on these tools—making the process more precise and consistent.
Plus, there’s less clutter in the work area while desoldering, which boosts efficiency and organization.
Removing Old Solder
It’s more challenging to melt solder as it ages, especially with a soldering iron and solder sucker.
However, the great thing about solder is that it hasn’t changed since its invention.
The materials we use have changed to form stronger connections, but modern solder melts similarly to old solder. You can melt it by applying a new solder layer atop the old one.
Remove it with a desolder technique mentioned above.
What Are Safety Precautions and Best Practices?
You should implement these safety guidelines when desoldering. They will help prevent damage and keep you out of danger.
Handling High Temperatures
If necessary, make sure the components cool down before heating them again.
This prevents excessive heat build-up, allowing them to function as normal.
Apply lower temperatures to sensitive components, like ICs, to avoid burns.
Attaching a tiny heat sink to the leads also helps with heat dissipation and protection.
Proper Tool Maintenance
Cleaning the soldering iron tip ensures better heat transfer, quickening the soldering and desoldering process.
If the tip has oxidization, it can make the task more challenging.
Regular maintenance prevents corrosion on the metal parts, extending their lifespan.
A contaminated tool can introduce debris, older solder, or flux to the newly formed joint.
This may lead to the formation of poor connections or short circuits.
General Safety Tips
Desoldering generates fumes that pose health risks if inhaled. Proper ventilation, like turning on the fan or opening a window, effectively pulls fumes away.
If that’s insufficient, a fume extractor helps by filtering fumes out of the air.
Wearing gear, like a respirator, safety glasses, and heat-resistant gloves, protects you against fumes.
Conclusion
Overall, the desoldering pump and braid wick are the most common desoldering techniques.
They provide easy removal processes. However, the braid wick type is more convenient for surface mount components as it requires precision.
Desoldering pumps, on the other hand, are designed for solder joints on through-hole components.
Be sure to go slow and carefully remove the solder. When it’s time, you must consider the techniques and apply the best safety measures.
This ensures that the circuit won’t get damaged—even if you choose the drilling method.
And you’ll be better off avoiding fume inhalation and burns to the eyes and skin by wearing the proper gear.
