How to Desolder a PCB Without Damaging It

What Must You Check Before Desoldering a PCB?

Determine if the PCB, component, or both should be preserved.

Identify whether you're recovering a low-value component from a PCB or a high-value component from a rare PCB.

Review the areas on the assembly that require desoldering. Locate and list any joints on the PCB that need to be desoldered, and check the back and front sides of the PCB for any copper planes, heat sinks, clips, adhesives, bent leads, and other heat-sensitive areas nearby.

Once you have identified all the areas you need to work on, isolate your assembly from electrical power and resolve any potential stored-energy hazards.

Select a tool based on your desired outcome for the assembly. Once the tool is selected, you will need to heat both the lead and the solder; remove solder only while it is molten, and confirm that each terminal is free before lifting the component. Stop if a pad moves, if you notice a change in the color of the laminate, if any nearby part shifts, or if removal requires excessive force. For electrical work where employees may contact live parts, OSHA requires de-energization and verification of the de-energized state where applicable (1910.333 Selection and Use of Work Practices). For this reason, this article does not cover high-voltage discharge. Stop work if the voltage, a damaged battery, or stored energy is unknown, and use a qualified person.

Keep your head and facial area out of the fume path while soldering. HSE states that fumes generated from rosin-based solder flux represent a respiratory hazard to workers and therefore suitable controls should be used, including fume extraction and avoiding unnecessary overheating (Electronics Soldering). HSE has reported that the concentration of rosin-based flux fumes can triple as the temperature of the soldering iron increases from 250°C to 400°C; therefore, blindly increasing the setpoint to compensate for poor heat transfer should be avoided (Controlling health risks from rosin (colophony)-based solder flux fume). Every effort should be made to provide adequate support to the PCB, protect the eyes from any flying debris generated by the soldering process, park hot tools in a safe location when not in use, and keep loose leads from springing toward the employee performing the work. ESD controls provide necessary protection for sensitive electronic components; however, they do not ensure the safety of working on energized electrical circuits. The EOS/ESD Association describes common-point or equipotential bonding between the work surface, personnel, and equipment for ESDS handling (EOS/ESD Fundamentals Part 3). ESD controls should only be applied after identifying and resolving electrical hazards.

It is important for a clean, tinned iron to transfer heat to the solder joint through a properly sized contact face. A braid removes modest amounts of surface solder, while a manual solder pump is used to remove an accessible pool of molten solder. When working with braid, match the wick width to fit the width of the soldered area and use a tip that has sufficient contact area to efficiently transfer the necessary heat to the braid; if the tip is too small or undersized, the amount of time required to heat the braid will be longer than necessary. When desoldering sensitive pads, leave the braid in place and move the hot iron over the braid rather than dragging the braid along the surfaces of the PCB (12 Easy Tips to Improve Your PCB Desoldering Process Today). Powered vacuum tools are useful for repeated or multi-pin through-hole work, while hot tweezers can release two-terminal SMD parts and controlled hot air can heat several visible terminals together. In addition to using the correct tools for desoldering, provide flux, a holder, a magnifying glass, and adequate light to support every desoldering technique.

The board remains stationary, it is easy to see and access the solder joints to be removed, the tip or nozzle fits the joint, the extraction tool will remove the molten solder, and inspection is possible to provide evidence of the release point prior to the lift.

Which Desoldering Method Fits the Joint?

A suitable desoldering tool for the task is capable of heating the entire joint, removing or holding the molten solder, and verifying the release point without applying excessive pressure or pulling force on the PCB.

An iron alone is appropriate for joint removal when a simple terminal can be released without using the component as a lever. Without solder extraction, the safe range of work is narrower. Under no circumstances should flames, consumer heat guns, or drills be used as improvised desoldering tools. The use of flames, consumer heat guns, or drills removes control over the land, barrel, laminate, and adjacent components.

SUGA-PCBA provides guidelines on through-hole assemblies using lead-and-barrel construction. Additionally, SUGA-PCBA provides guidelines on SMT assemblies, which may require heating multiple terminals simultaneously.

A Release-First PCB Desoldering Procedure

In desoldering a PCB, advance through the stages by the observed state of the joint instead of by a set time. If there is no visible output, stop and address the current state of the joint before increasing force or adding additional heat without determining what caused the missing output.

The HAKKO FR-410 manual indicates that the nozzle should heat the lead and solder. It also provides a caution to avoid contact that could cause the land to peel. The manual also calls for confirmation of full melt and free movement of the lead prior to suction from the joint. These instructions are product-specific, but the observed release tests are useful beyond that specific product.

In general, three states of through-hole desoldering should be distinguished. Surface solder may be removed while solder remains on the barrel wall, and even a clear-looking opening does not confirm that the lead is free. If one attempt leaves the lead bonded, you can add a small amount of compatible fresh solder to achieve better wetting and thus a better thermal bridge; where the applicable process permits, the addition of compatible flux can further improve wetting. Reheat the entire joint, ensure that the solder is completely liquid through the barrel, and extract again. Continued attempts never equal permission to pull.

With multi-pin sockets and connectors, the consequences of one missed joint become magnified. It's best to verify the release of every lead individually. Instead of relying on repeated manual cycles to remove difficult components, a powered vacuum process may protect the PCB better than multiple manual attempts. For inexpensive components versus valuable PCBs, a controlled sacrificial removal method can reduce stress on the board; if there is a disposable through-hole part that is easily accessible, cut the leads and remove any remaining pins one by one if the repair procedure permits. There is no reason to cut or drill into a PCB without having a qualified procedure to do it correctly.

When working on SMDs, the removal method depends on terminal visibility. Two-terminal parts and components with visible leads can be removed when all terminals are molten together and nearby components remain fixed. The vacuum pick-up method described in the FR-811 manual from HAKKO provides a method for removing SMDs after melting the solder.

Bottom-terminated packages should be handled differently. As described by Texas Instruments, equipment, PCB thickness, thermal mass, package size, and moisture can affect the removal profile and the risk of delamination during removal. Additional recommendations from TI regarding LLP include using localized heat, providing bottom preheat, vacuum pickup, aligning components, and inspecting after removal. One of the specific recommendations from TI related to an LLP chip-scale package is to bake the circuit board before rework to help remove residual moisture. This specific amount of time, i.e. 4 hours at 125°C, is associated with one specific family of packages; however, the specific package, PCB, and process specifications will ultimately determine the bake requirements for anything else on your bench. You should not confuse the method for the removal of QFN or BGA packages with using a standard household heat gun.

Why Won't the Solder Melt or Leave the Hole?

The temperature setpoint on the station display does not indicate how much heat actually reached the solder joint through the tip, land, and nearby copper. The free flow of solder does not confirm that the pump sealed, the barrel cleared, or the lead released. These are three separate faults related to whether solder can be removed successfully, not one.

These values refer to the melting temperatures for a range of solder alloys. Do not use these values as recommended temperatures for setting your soldering iron. Tool settings are based on the geometry of the tip or nozzle, the quality of the contact, the thermal mass of the board, the airflow, and the calibration of the tool.

Reduced heat transfer or wetting on a surface could be due to an oxidized surface, an unfamiliar alloy, a large amount of copper acting as a heat sink, or access problems. Increasing the size of the contact face, improving wetting, using a more capable station, controlling the preheat, or using a powered vacuum may all be appropriate fixes under an approved process. Raising the temperature without addressing the cause can increase the chance of damaging the pad and laminate while not providing better heat transfer.

If, after the component has been removed, you still see solder in a hole, you should use an approved extraction technique that protects the barrel from damage. Drilling through the hole can damage the plated copper and should not be used as a default beginner method. If you cannot get the solder out using controlled heat, proper extraction, a stable supporting base, and proper inspection methods, you should stop and move on to a qualified PTH repair process.

When Should You Stop Before the PCB Is Damaged?

Visible or physical evidence of a moving land, discoloration, blistering, delamination, a shifting nearby part, repeated failed cycles, or a lead that will not move freely indicates that you should stop. These are signals that there is a need to improve the procedure used to support the part, provide heat to it, or inspect the joint.

You should also stop when your goals change regarding saving both the board and part. If you believe there is no reasonable expectation to save both, you should not silently decide which item you will sacrifice. You should evaluate the relative values of both items, your authority, inspection access, and downstream acceptance. Your documentation for any production work should reflect your decision before cutting any part, altering any lead, using a nonstandard alloy, or starting a formal repair process on either a component or PTH.

Inspect the Board and Component Separately

Separating a component does not establish board acceptance or allow component reuse. Inspect the board and component separately using the released product acceptance specifications and applicable component criteria.

TI's surface-mount removal note indicates that components removed under its stated failure-analysis process are not to be reused. This means that the no-reuse rule is specific to that stated process. If you were to treat this rule as a catch-all for every removed component, it would eliminate the other factors, such as datasheet limits, condition reviews, and history checks, that would determine the ability to reuse a removed component.

The IPC Revision Table identifies IPC-7711/21D as the current rework, modification, and repair document, and IPC certification information indicates coverage of removing and repairing through-hole and surface-mount components.

The J-STD-001J standard governs soldered-assembly process and material requirements, while the IPC-A-610J standard defines visual acceptability requirements for electronic assemblies.

Production release may require the use of an approved procedure, trained personnel, material controls, inspection methods, acceptance criteria, and a traceable record of the disposition of the board.