Activity 1.1.9 — Desoldering and Circuit Repair¶

Learning Objectives¶

By the end of this lesson, students will be able to:

Identify situations that require desoldering and the tools needed.
Demonstrate proper technique for using a solder sucker (desoldering pump).
Demonstrate proper technique for using solder wick (desoldering braid).
Remove through-hole components safely without damaging the circuit board.
Recognize and avoid common problems during desoldering.

Vocabulary¶

Vocabulary (click to expand)

Term	Definition
Desoldering	The process of removing solder from a joint to disconnect or extract a component
Solder Sucker	A spring-loaded tool that creates suction to vacuum up molten solder (also called desoldering pump)
Solder Wick	A braided copper wire that absorbs liquid solder through capillary action (also called desoldering braid)
Hot Air Rework Station	A tool that blows hot air to melt solder on surface-mount components
Through-Hole	Component leads that pass through holes in the circuit board and are soldered on the opposite side
Surface-Mount (SMD)	Components mounted directly on the surface of the circuit board without holes
Flux	A chemical cleaning agent that promotes solder flow and wetting; essential for good desoldering
Thermal Shock	Rapid temperature change that can crack or damage components and circuit boards

Part 1: When to Desolder¶

Desoldering is a critical skill for any electronics work. Knowing when and why to desolder helps you decide if it is the right approach.

Common Reasons for Desoldering¶

Reason	Description	Difficulty
Component Mistake	Wrong component placed or placed incorrectly	Moderate
Component Failure	Removing a damaged component to replace it	Moderate
Component Reuse	Removing working components for salvage or reuse	Moderate
Circuit Modification	Changing component values or circuit connections	Moderate to Difficult
Repair Work	Accessing internal joints for repair	Difficult
Debugging	Temporarily removing components to test circuit sections	Moderate

Is Desoldering the Right Choice?¶

Consider these factors before desoldering:

Time investment: Desoldering takes 5-10x longer than soldering. Is the component worth it?
Component condition: Is the component likely to still work after removal?
Board condition: Will the board survive the process? Older boards are more fragile.
Alternative approaches: Can you work around the component instead of removing it?

Key insight: Not every mistake requires desoldering. Sometimes it is faster to add a new component in a different location or to cut traces and add wire jumpers rather than removing a part.

Part 2: Desoldering Tools Overview¶

Having the right tools makes desoldering faster, cleaner, and less likely to damage the board.

Tool 1: Solder Sucker (Desoldering Pump)¶

How it works: A spring-loaded piston creates suction when released, vacuuming up molten solder.

Best for: Through-hole components, cleaning solder from holes, quick cleanup jobs.

Types: | Type | Pros | Cons | |------|------|------| | Bulb style | Simple, cheap, no maintenance | Weak suction, hard to control | | Piston style | Strong suction, precise control | Requires two hands to operate | | Electric | Very strong suction, one-hand operation | Expensive, requires power |

Using a Piston Solder Sucker:

Step 1: Press the plunger down until it clicks/locks
Step 2: Heat the solder joint with the iron
Step 3: Touch the solder sucker tip to molten solder
Step 4: Press the release button to create suction
Step 5: Solder is vacuumed into the barrel
Step 6: Clear the barrel before next use

Tool 2: Solder Wick (Desoldering Braid)¶

How it works: The braided copper wire absorbs molten solder through capillary action.

Best for: Removing small amounts of solder, fixing bridges, working near heat-sensitive components.

Features: - Rosin-coated wick (purple or white) promotes solder flow - No-clean wick (green) leaves minimal residue - Various widths: narrow for fine pins, wide for large pads

Using Solder Wick:

Step 1: Place the end of the wick on top of the solder joint
Step 2: Apply the soldering iron tip to the wick above the joint
Step 3: Heat transfers through the wick to the solder
Step 4: Solder wicks up the braid (capillary action)
Step 5: Remove the wick while still heated
Step 6: Cut off the used portion of wick and repeat if needed

Tool 3: Hot Air Rework Station¶

How it works: A stream of hot air melts solder on surface-mount components from all angles simultaneously.

Best for: Surface-mount devices (SMDs), ICs, components with many pins.

Settings: | Application | Temperature | Airflow | |-------------|-------------|---------| | Small SMD components | 300-350C | Low-Medium | | ICs/Chips | 350-400C | Medium | | Large connectors | 400-450C | Medium-High | | Lead-free solder | Add 20-30C | Same |

Safety note: Hot air stations can damage nearby components from indirect heat. Use a heat shield or nozzle when working near sensitive parts.

Tool 4: Supporting Tools¶

Tool	Purpose
Flux pen or paste	Improves solder flow and wetting during desoldering
Tweezers	Handling small components, prying up lifted parts
Solder wick holder	Holds wick in place for one-hand operation
Chip hook or probe	Lifting components after solder melts
Magnification	Examining small joints for bridges or residue

Part 3: Desoldering Through-Hole Components¶

Through-hole components have leads that pass through holes in the circuit board. Removing them requires clearing the solder from the holes.

Method 1: Solder Sucker Technique¶

Best for: Single and dual-pin components (resistors, diodes, small capacitors)

Procedure: 1. Prepare: Place the board securely in a holder or vise. 2. Heat one pin: Apply the iron tip to the first pin lead on the component side. 3. Wait for melting: Hold for 2-3 seconds until solder is liquid. 4. Activate sucker: Touch the solder sucker tip to the molten solder and release the plunger. 5. Repeat: Do the same pin again to clear any remaining solder. 6. Move to second pin: Repeat steps 2-5 for the second pin. 7. Test: Gently try to lift the component. If it does not move, clear the other side of the hole. 8. Remove: Once both holes are clear, lift the component out.

Method 2: Solder Wick Technique¶

Best for: When solder sucker is not available, or for stubborn joints

Procedure: 1. Cut a length of wick: Use about 5-8 cm of desoldering braid. 2. Position the wick: Place the end of the braid directly on top of the solder joint. 3. Apply heat: Place the iron tip on top of the braid, not the joint directly. 4. Let capillary action work: The solder will flow up into the braid. 5. Remove together: Lift the wick and iron simultaneously. 6. Check the joint: If solder remains, use a fresh section of braid and repeat. 7. Clear both holes: Repeat the process for all component leads.

Method 3: Combination Technique (Most Reliable)¶

For components with multiple pins or stubborn solder joints, combine both tools:

Apply flux: A little flux on the joint improves solder flow.
Heat and suck: Use the solder sucker first to remove bulk solder.
Finish with wick: Use solder wick to clear any remaining residue from holes.
Repeat for all pins: Work through each pin systematically.

Key insight: Patience is essential. Do not try to remove the component until each hole is completely clear. Forcing it damages both the component and the board.

Part 4: Desoldering Multi-Pin Components¶

Components with many pins (connectors, switches, ICs) require a different approach.

Removing Multi-Pin Through-Hole Components¶

Tips for multi-pin removal:

Start with flux: Apply flux to all pins to promote solder flow.
Work in rows: Clear solder from one row of pins at a time.
Use wick for remaining solder: After suction, use wick to clean up.
Alternate sides: Remove some pins from each side to avoid stressing the component.
Test each pin: Gently try to move the component after clearing each pin.
Clear stuck pins: If only one or two pins hold, clear those specifically.
Lift carefully: Once loose, lift the component straight up to avoid bent leads.

Removing Connectors with Lots of Solder¶

Some connectors have large pads that hold a lot of solder. For these:

Heat from bottom: Use a larger tip to heat the connector from the solder side.
Use a solder sucker: Remove bulk solder from the large pads.
Apply heat while pulling: Heat one section while gently prying with tweezers.
Work around: Move to adjacent sections and repeat.
Never force: If it does not move, more solder or heat is needed.

Part 5: Desoldering Surface-Mount Components¶

Surface-mount devices (SMDs) are mounted directly on the board surface without holes. Removing them requires different tools and techniques.

Method 1: Hot Air Station (Preferred for SMDs)¶

Best for: All SMD components, especially ICs and multi-pin parts

Procedure: 1. Set temperature and airflow: Start with 350C and medium airflow. 2. Select appropriate nozzle: Use a nozzle that focuses air on the component. 3. Apply flux (optional): Add flux to the component leads if accessible. 4. Heat the component: Direct hot air at the component, moving slowly across it. 5. Watch for solder melting: You will see the component start to shift slightly. 6. Lift the component: Once solder is liquid, use tweezers to lift the component. 7. Clean the pads: Immediately clean remaining solder with wick or hot air.

Method 2: Soldering Iron + Solder Wick (For 2-3 Pin SMDs)¶

Best for: Resistors, capacitors, diodes with 2-3 leads

Procedure: 1. Add fresh solder: A little fresh solder helps promote flow. 2. Apply wick: Place solder wick over the component leads. 3. Apply heat: Use the iron tip to heat the wick and leads simultaneously. 4. Remove solder: Solder flows into the wick. 5. Lift component: Once leads are free, lift the component with tweezers. 6. Clean up: Use fresh wick to clean any remaining solder from pads.

Method 3: Soldering Iron Drag Method (For ICs)¶

For ICs with many pins: 1. Add solder: Flood all the pins with fresh solder to bridge them. 2. Heat and drag: Use the iron to heat multiple pins at once while dragging across. 3. Alternate: Heat one row, then the opposite row. 4. Lift when loose: Once all pins are liquid, lift the IC. 5. Clean pads: Remove solder from all pad locations with wick.

Part 6: Common Problems and Troubleshooting¶

Problem 1: Lifted Pads¶

What happens: The copper pad separates from the circuit board substrate.

Cause: Too much heat, applying force before solder fully melts, dragging the iron.

How to avoid: - Use appropriate temperature (not too high) - Never pull or pry until solder is completely liquid - Use flux to reduce necessary heat - Use solder sucker instead of iron for removal when possible

How to repair (if it happens): - Carefully scrape away solder from the lifted pad and trace - Use conductive epoxy or wire to reconnect the trace - This repair is challenging and may require professional help

Problem 2: Remaining Solder in Holes¶

What happens: After desoldering, the hole is still blocked with solder.

Cause: Insufficient heat, cold solder not removed, too much solder originally.

Solutions: - Reheat the hole and use the solder sucker immediately - Apply fresh solder (it helps flow) and try again - Use solder wick to clear the hole - Combine heat, wick, and iron for stubborn cases

Problem 3: Component Damage¶

What happens: The component is destroyed during removal and cannot be reused.

Causes: - Too much heat (thermal damage) - Excessive force (bent or broken leads) - Wrong technique for the component type

Prevention: - Research the component and plan your approach - Use temperature-controlled equipment - Never force removal — patience prevents damage

Problem 4: Bridge Formation During Desoldering¶

What happens: New solder bridges form while trying to remove solder.

Cause: Spreading solder with iron or wick.

Solution: - Apply flux first to help solder flow properly - Use solder sucker to remove solder rather than spreading - Use fresh wick for each application

Problem 5: Damaged Traces¶

What happens: The copper trace on the board is lifted, scratched, or burned.

Cause: Excessive heat, scraping with tools, mechanical stress.

Prevention: - Use appropriate temperatures - Never scrape the board surface - Apply heat only where needed, not across large areas

Key insight: The most common cause of desoldering damage is rushing. Take your time, use the right temperature, and never force anything.

Part 7: Desoldering Tips and Best Practices¶

General Tips¶

Use flux liberally. Flux is your friend. Apply it before, during, and after desoldering. It helps solder flow and makes everything easier.
Use the right temperature. Higher is not better. Too much heat damages components and boards. Start lower and increase only if needed.
Clear holes completely. Do not remove a component until the holes are completely clear. Test by inserting a pin or thin wire.
Work in good lighting. Small solder joints are hard to see. Use a lamp or magnification.
Keep tools clean. A dirty tip or clogged solder sucker will not work properly. Clean regularly.
Practice on scrap boards first. If possible, practice desoldering on old, non-working boards before attempting repairs on valuable equipment.
Let things cool. After desoldering, let components and boards cool between joints to prevent thermal shock.

Flux Application Tips¶

Situation	Recommended Flux Type
General through-hole	Rosin flux pen or paste
Surface-mount	Flux paste applied with syringe
Lead-free solder	Extra flux recommended
After solder removal	Apply flux before adding new solder

When to Stop and Seek Help¶

Consider asking for assistance or using professional services if: - The board is very old or valuable - Multiple layers are involved (multilayer PCBs) - The component is extremely heat-sensitive - You have already damaged the board once - The repair requires micro-soldering skills

Part 8: Practice Exercises¶

Practice Exercise 1: Removing a Resistor from a Practice Board¶

Objective: Successfully remove a through-hole resistor without damaging the board or resistor.

Materials: Practice circuit board with through-hole resistors, solder sucker, solder wick, soldering iron, flux

Procedure: 1. Apply flux to both resistor leads. 2. Heat one lead and use the solder sucker to remove solder. 3. Repeat for the same lead to ensure the hole is clear. 4. Do the same for the second lead. 5. Gently attempt to lift the resistor. 6. If it does not move, clear the holes again. 7. Once loose, lift the resistor straight up. 8. Clean any remaining solder from the holes. 9. Save the resistor for reuse if possible.

Evaluation Criteria: - [ ] Both holes are clear of solder - [ ] No lifted or damaged pads - [ ] Resistor leads are intact and not bent - [ ] Resistor is undamaged and can be reused

Practice Exercise 2: Cleaning Solder from Empty Pads¶

Objective: Clear solder from holes without a component, simulating prep for a new component.

Materials: Practice board with solder-filled holes (no component), solder sucker, solder wick, soldering iron, flux

Procedure: 1. Apply flux to the filled hole. 2. Use the solder sucker to remove bulk solder. 3. Use solder wick to remove remaining residue. 4. Inspect the hole under magnification. 5. If any solder remains, repeat the process. 6. Verify the hole is clear by inserting a wire or component lead.

Evaluation Criteria: - [ ] Hole is completely clear - [ ] No damage to pad or surrounding traces - [ ] Pad remains properly attached to board - [ ] Hole is ready to accept a new component

Practice Problem — Desoldering Situation Analysis¶

Scenario: You need to remove a dual in-line (DIP) integrated circuit from a circuit board. The IC has 14 pins, and you only have a soldering iron and solder wick (no solder sucker or hot air station).

What approach would you take?

Show Solution

Step-by-step approach for IC removal with iron and wick only:

Prepare the workspace: Ensure good lighting and secure the board.
Apply flux: Apply flux liberally to all 14 pins. This will help solder flow when heated.
Work systematically:
Start on one side of the IC and work across, then the other side.
Clear a few pins at a time rather than trying to do all at once.
Clear each pin with wick:
Place the solder wick on top of the first pin.
Apply the iron tip to the wick to transfer heat.
The solder will wick up into the braid.
Remove the wick while still heated.
Cut off used portion of wick and repeat.
Alternate sides: Do not remove pins from only one side. Alternate between sides to avoid stressing the IC.
Test as you go: After clearing each pin, try to gently lift that side of the IC slightly. This tells you when pins are free.
Final removal: Once enough pins are cleared, the IC should lift out. If only 1-2 pins hold, clear those specifically.
Clean the pads: After removal, use fresh wick to clear any remaining solder from the 14 pad locations.

Time expectation: This process will take significantly longer than using a solder sucker or hot air station. Budget 10-15 minutes for careful removal.

Summary¶

Topic	Key Points
Solder Sucker	Spring-loaded vacuum tool for removing bulk solder; fast but requires two hands
Solder Wick	Copper braid that absorbs solder via capillary action; precise but slower
Hot Air Station	Best for SMD components; melts solder from all angles simultaneously
Through-Hole Removal	Clear one pin at a time, then lift; never force
SMD Removal	Hot air is preferred; use iron + wick for small components
Common Problems	Lifted pads, remaining solder, component damage, bridges
Best Practice	Flux first, right temperature, patience, never force

Quick Reference — Tool Selection Guide¶

Situation	Recommended Tool
Single through-hole pin	Solder sucker
Cleaning solder from holes	Solder wick
Surface-mount component	Hot air station
Small 2-3 pin SMD	Soldering iron + wick
Multi-pin IC	Hot air station (preferred)
Fixed bridges	Solder wick
Quick cleanup	Solder sucker

Quick Reference — Temperature Guidelines¶

Application	Temperature (Celsius)
Through-hole desoldering	350-380C
SMD with hot air	350-400C
Lead-free solder	Add 20-30C
Heat-sensitive components	Use lowest effective temp

Key Reminders¶

Desoldering is slower than soldering — budget extra time and be patient.
Use flux liberally — it makes solder flow better and reduces heat requirements.
Never force component removal. If it does not move, the solder is not fully melted.
Clear holes completely before attempting to lift components.
The most common desoldering mistakes are lifted pads and thermal damage — use appropriate temperatures.
Practice on scrap boards before attempting repairs on valuable equipment.
Solder sucker removes bulk solder quickly; wick cleans up remaining residue.
Hot air stations are essential for SMD work but can damage nearby components.

Custom activity — adapted from PLTW Digital Electronics