Solder Wick Desoldering Technique For PCB Rework

Solder wick is a braid of fine copper strands that is used to remove molten solder from a joint. The braid is placed over the solder, heated from above with a soldering iron, and the molten alloy is drawn into the braid by capillary action, leaving the pad and the lead clean.

It is the most common desoldering method in a rework station because it is cheap, fast for small joints, and needs nothing beyond an iron. It is also the method that causes most pad damage, because the heat needed to melt a joint is applied through a material that conducts it away.

What Solder Wick Is

The braid is made from many fine copper strands woven together, with a flux coating or a flux core that activates as it is heated. The strand count determines how much solder the wick can absorb per unit length, and the weave determines how evenly the heat spreads across the contact area.

Wick is supplied on a spool in a range of widths, and it is normally used once and cut away. Reusing a loaded section is a common mistake, because the solder already in the braid reduces its capacity and forces the operator to apply more heat than the joint needs.

How Heat Transfer Works

The iron tip contacts the top of the braid and the braid contacts the joint. Heat flows through the braid to the solder, and the braid also acts as a heat sink that carries energy away from the joint towards the surrounding copper, which is the opposite of what the operator wants.

That is why the tip has to be large enough and hot enough. A small tip on a wide braid cannot deliver heat faster than the braid dissipates it, so the solder never melts properly and the operator ends up holding the iron on the joint for far too long.

Choosing The Right Width

The width of the braid should roughly match the size of the joint. A braid that is much wider than the pad transfers heat into the surrounding laminate and into adjacent joints, while one that is much narrower cannot absorb all the solder in a single pass.

For a fine pitch row, a narrow wick of 1 to 1.5 mm is used and the joints are cleared one at a time. For a through hole pin or a large tab, a 2 to 3 mm braid is faster and needs a large chisel tip to drive it.

Flux And Its Role

Flux reduces the oxide on the joint and on the braid so that the molten solder wets both. Most wick is supplied with a rosin or a no-clean flux coating, and the coating is what makes the first few centimetres work much better than the rest of the spool.

Adding liquid flux to the joint before applying the wick improves the result considerably, particularly on a joint that has already been heated once. The flux should be the same type as the one used in assembly, so that the residue left behind is compatible with the cleaning process.

Technique Step By Step

The iron is set to a temperature at the high end of the working range, typically 350 to 380 C for a lead free joint, and the tip is tinned and wiped. The braid is laid over the joint, the tip is pressed down onto the braid, and the assembly is left alone until the solder flows visibly into the braid.

The wick is then lifted away together with the iron in one movement, so that the joint does not re-solidify with the braid still attached. If solder remains, a fresh section of braid is used rather than the loaded one, because the second pass needs the same clean capillary action.

Avoiding Pad Damage

Pad damage almost always comes from time and temperature rather than from the wick itself. Every additional second at temperature weakens the adhesive between the copper and the laminate, and a pad that is lifted will not go back down.

The practical controls are a large enough tip, a fresh piece of braid and a limit on how long the iron stays on the joint. If the solder has not flowed within a few seconds, the correct response is to stop, add flux and try again rather than to hold the iron in place.

Through Hole Versus Surface Mount

A through hole pin is the easiest case, because the solder is accessible from both sides and there is usually more of it. Removing a component from a plated hole needs the barrel to be emptied, which may require wick from one side and a hot iron from the other.

A surface mount pad is more delicate, because the pad is held only by the laminate and it is close to its neighbours. On a fine pitch device, wick is often the wrong tool and a hot air station or a dedicated desoldering tool gives better control.

Cleaning And Inspection

After desoldering, the area is cleaned to remove the flux residue that the wick left behind. The residue is more concentrated than after assembly, because the flux has been heated more than once, and it can be conductive if it is left in place.

Inspection looks for a lifted pad edge, for solder left in a plated barrel, and for thermal damage to the mask or the laminate. Any of those indicates that the removal was too aggressive. How the rework is recorded is described under PCB design quality characteristics.

Alternatives To Wick

A vacuum desoldering tool removes solder from a plated barrel without the mechanical contact of a braid, which makes it the better choice for a through hole pin in a thick board. It is more expensive and needs more maintenance, but it is much gentler.

Hot air and infrared stations are used for surface mount parts with many leads, where a braid would be impractical. The choice of method should follow the package and the number of joints, not habit. The related pad rules are described under PCB pad design standards.

Wick Versus A Desoldering Pump

A manual desoldering pump is a spring loaded vacuum syringe that draws the molten solder out of the joint. It is faster than wick on a large through hole joint and leaves less flux residue behind, but it cannot clear a fine pitch pad and it needs a good seal against the barrel to work at all.

Where a plated barrel has to be emptied, the pump is usually the better first tool and wick is used afterwards to remove what is left. The combination is faster and gentler than using wick alone for the whole operation. Rework access is itself a layout decision, described under layout decisions that affect production.

FAQ

Can wick be reused? A section that is already loaded with solder should be discarded. Reusing it slows the removal, encourages the operator to apply more heat, and increases the risk of lifting a pad.

What temperature should the iron be set to? Around 350 to 380 C for a lead free joint is a practical working range. Higher temperatures shorten the time needed but also shorten the margin before damage occurs.

Does wick leave residue on the board? It does, because the braid carries flux. The area should be cleaned after rework with the same process used for the assembly, and the residue should be checked visually.