What Is Desoldering Wick and When Should You Use It?

2022-07-01 18:57:04 By : Ms. River He

When you need to remove components for a PCB repair, desoldering wick is a useful tool. Here's how to use it.

Building a PCB assembly from scratch requires a soldering iron. However, repairing one involves desoldering faulty components before soldering can even begin. The desoldering wick (also called desoldering braid or solder wick) is one of the two major desoldering tools, with the other being the desoldering pump.

But which one of these should be in your soldering kit? That also begs the question: are desoldering wicks and pumps mutually exclusive, or do you need both? Understanding how and when to use a desoldering wick is key to answering these questions.

While a solder sucker is a mechanical device that sucks molten solder off the PCB, a desoldering wick is a consumable item that absorbs solder into itself. It is also called a desoldering braid because it is essentially a length of braided copper wire. The flat ribbon is sold in spools of various lengths and fashioned out of extremely fine copper strands woven in a crisscross pattern.

A desoldering wick’s ability to absorb solder is enhanced by infusing the copper strands with a generous helping of flux. It is used in conjunction with a soldering iron, where the heat from the tip allows solder to be wicked off component leads and PCB pads by the means of capillary action. Once a section of the desoldering wick gets saturated with solder, it can be quickly snipped off to reveal fresh copper further along the spool.

While a solder sucker (or desoldering pump) operates like a vacuum cleaner, a desoldering wick is more like a mop. The latter’s ability to absorb solder makes it indispensable in applications where solder splatter is unacceptable.

This also makes the desoldering wick inherently better at cleaning solder off SMT (surface-mount technology) pads and also at removing solder bridges on fine-pitch SMT and BGA (ball grid array) pads found on modern PCBs populated with SMD (surface-mount device) components. Although SMD components are best desoldered using a hot air rework station or specialized desoldering tweezers, a desoldering wick can also be used in a pinch for the task.

A desoldering pump, on the other hand, is practically useless for any kind of SMD rework. That’s because the conductive pads on the PCB are too flat to allow solder to be sucked out effectively. It’s a bit like drinking soup off a dinner plate through a straw.

However, solder suckers are better at desoldering PTH (plated through-hole) joints. A desoldering wick can also get the job done, but its capillary action isn’t efficient at absorbing a large amount of solder from the deep cylindrical cavity of a PTH joint. The added thermal mass of the copper braid and the large PTH joint increases dwell time, which is harmful for both the components and the copper traces on the PCB.

A solder sucker is, therefore, quicker and safer for desoldering PTH joints – as detailed in our guide on how to use a solder sucker. However, it cannot wipe PTH pads clean following a desoldering job. The desoldering wick is still indispensable for cleaning residual solder off PTH boards—just like you have to mop a floor even after you have vacuumed it.

Desoldering wicks are typically sold in 1.5 meter (5 ft) and 3 meter (10 ft) spools, which are also referred to as bobbins. Larger spools can range from anywhere between 25 ft and 500 ft, but such large quantities aren’t suitable for hobbyists. Length is a matter of convenience, but choosing the correct width is a more important consideration.

Desoldering wicks are available in a wide range of widths starting at 0.8 mm and going beyond 5 mm. As a rule of thumb, the braid width should be either equal to the pad size, or only slightly larger. Smaller braids won’t be able to wick solder off the entire pad, whereas oversized ones will affect neighboring pads you don’t intend to desolder.

Smaller braid widths also force the user to move them around while desoldering. This elevates the risk of scratching and delaminating the pads off the PCB. A desoldering wick that’s excessively wider also increases thermal mass and prolongs the dwell time on components. Again, this increases the risk of damage to components and the PCB pads.

The same logic also applies to the soldering iron tip. It should ideally match the braid width. Too small and heating is slower, which increases dwell time and risk of damage to components. Oversized tips, on the other hand, can knock off neighboring components.

Chisel, knife, and hoof tips are best suited for this job. Avoid using conical tips: their small contact patch leads to poor thermal linkage.

Finally, the flux composition used in the desoldering wick is also important. If your workflow relies on using no-clean solder, because you wish to skip cleaning, you must use a desoldering wick that has been infused with no-clean flux. If you plan on cleaning your PCB assembly post rework, desoldering wicks imbued with rosin flux have the quickest wicking action.

Desoldering wicks are also available with no added flux for highly specialized rework processes. This allows you to use your own flux, which is usually done to avoid the risk of contamination.

The general desoldering strategy is practically the same for all tasks. Here’s how to use a desoldering wick the right way.

Heat the soldering iron to the desired temperature. This depends on the following factors.

Modern electronic devices use lead-free solder. Such joints require tip temperatures in the range of 570 °F (300 °C) to 660 °F (350 °C). DIY PCBs employing lead solder require lower tip temperatures ranging from 520 °F (270 °C) to 570 °F (300 °C). Learn more about the correct soldering temperature in our handy guide.

Make sure your soldering iron tip is tinned. Use our soldering tip tinning guide to ensure that the tip of your soldering iron is properly tinned.

If you plan on using an unfluxed desoldering wick, you must apply flux to all joints (or pads) meant to be desoldered. Generally speaking, supplying additional flux makes it significantly easier to desolder stubborn joints irrespective of the type of desoldering wick used.

Place the desoldering wick on the joint (or pad).

Do not hold the wick with your bare hands. It gets extremely hot, so either handle it by the spool or use a pair of tweezers.

Gently rest the soldering iron tip on the wick. Angle the tip to maximize the contact patch. This improves thermal linkage and does the job quicker while minimizing component damage.

Apply minimal pressure on the desoldering wick with your soldering iron. Hold for a few seconds until the solder melts and is subsequently wicked into the desoldering braid.

After a few seconds, the section of desoldering wick will change its color from copper to silver. This indicates that it has been saturated with solder.

Lift both the desoldering wick and the soldering iron tip off the PCB at the same time. Removing only the soldering iron will solder the braid to the PCB. If that happens, reapply flux to the braid and reheat the stuck section with the soldering iron. The wick and tip can now be simultaneously lifted off the PCB.

Inspect the joint. If it has been desoldered, move on to the next joint. Either way, it’s important to snip off the used section of desoldering wick with a pair of flush cutters before attempting to repeat the process.

Congratulations! You have acquired the skill to desolder components and clean up PCB pads using a desoldering wick. The fairly simple process works on everything, ranging from desoldering PCB components and wire terminals to cleaning pads and removing solder bridges.

Nachiket has covered diverse technology beats ranging from video games and PC hardware to smartphones and DIY over a career spanning 15 years. Some say that his DIY articles serve as an excuse to pass off his 3D printer, custom keyboard, and RC addiction as “business expenses” to the wife.

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