Rework & Repair Techniques#

Once the faulty component is identified, the next step is removing it and installing a replacement without damaging the board. Rework is a manual skill — reading about it helps, but practice on scrap boards is essential.

Through-Hole Desoldering#

Solder Sucker (Desoldering Pump)#

Best for: through-hole pins, large pads, clearing plated-through holes.

  1. Heat the joint with the iron until the solder is fully molten
  2. While holding the iron on the joint, bring the solder sucker tip right next to the joint
  3. Release the pump — it sucks the molten solder away
  4. Repeat if needed. Some joints take 2–3 passes
  5. Gently wiggle the component to check if it’s free

Tips:

  • Keep the sucker tip clean and the seal intact — a worn tip loses suction
  • Heat from one side, suck from the same side. Don’t try to heat from the front and suck from the back
  • If the hole is still plugged, add fresh solder (to improve thermal contact and add flux), then suck again

Solder Wick (Desoldering Braid)#

Best for: cleaning up pads, removing solder bridges, through-hole joints where the sucker can’t reach.

  1. Place the wick on the joint
  2. Press the hot iron on top of the wick
  3. The wick draws solder up by capillary action
  4. Lift wick and iron together — don’t drag the wick while it’s soldered to the pad

Tips:

  • Use the right width wick for the job — too narrow is slow, too wide steals heat
  • Add a touch of flux to the wick if it’s not picking up solder well
  • Fresh wick works much better than the end that’s already saturated — clip off the used portion

Pad Care#

Through-hole pads and traces are bonded to the board with adhesive and copper plating. They can lift under too much force or heat.

  • Don’t pry components out. If it’s not free, remove more solder
  • Limit heat time — a few seconds per pad. If it’s not working, let the board cool and try again
  • If a pad lifts, it can sometimes be glued back with cyanoacrylate (super glue) and re-soldered carefully. If the trace is broken, a jumper wire is needed

SMD Replacement#

Two-Terminal Components (Resistors, Caps, Diodes)#

The simplest SMD rework. Two approaches:

Iron method:

  1. Add fresh solder to both pads (more solder = more thermal mass = more working time)
  2. Touch one pad with the iron to melt it, then slide the tip to the other pad
  3. With a steady hand, alternate between pads quickly until both are molten simultaneously
  4. Lift the component away with tweezers
  5. Clean the pads with wick
  6. Tack the new component on one pad first, then solder the other

Hot air method:

  1. Apply flux to both pads
  2. Heat evenly with hot air until solder melts
  3. Lift component with tweezers
  4. Clean pads, place new component, tack and solder

Multi-Pin ICs (SOIC, TSSOP, QFP)#

Removal:

  1. Apply flux generously to all pins
  2. For SOIC (8–16 pins): add solder to bridge all pins on one side, then heat with the iron to melt the whole bridge and lift that side. Repeat for the other side
  3. For QFP (many fine-pitch pins): hot air is usually easier. Shield nearby components with kapton tape or aluminum foil, apply flux, heat evenly, lift when all pins are molten

Installation (drag soldering):

  1. Clean and tin the pads lightly
  2. Align the new IC carefully — get pin 1 orientation right!
  3. Tack one corner pin
  4. Check alignment. Adjust if needed (reheat the tack pin)
  5. Tack the opposite corner
  6. Apply flux to the remaining pins
  7. With a fine tip and a small amount of solder on the iron, drag across the pins. The flux and surface tension pull solder to the pads and away from the gaps between pins
  8. Inspect for bridges under magnification

QFN and BGA#

These packages have pads underneath, not on the sides. An iron alone cannot rework them.

QFN: Hot air is the standard approach. Apply flux, heat from above evenly. The part will visibly settle when the solder melts. For removal, lift with tweezers once molten.

BGA: Requires controlled hot air (ideally a rework station with a nozzle matched to the package), solder paste or preforms for re-balling, and good alignment. This is advanced rework — practice on scrap before attempting it on a board that matters.

Temperature guidance:

  • Lead-free solder: 240–260°C peak (hot air station set higher to account for airflow losses)
  • Leaded solder: 200–220°C peak
  • Always preheat the board to ~100–150°C to reduce thermal shock and warp

Lifted Pads and Trace Repair#

When a pad lifts or a trace breaks, the electrical connection needs to be restored.

Trace Repair#

  1. Scrape the solder mask to expose bare copper on both sides of the break (use a hobby knife carefully)
  2. Tin the exposed copper
  3. Bridge with a short piece of fine wire (30 AWG wire-wrap wire works well), soldered to both exposed copper areas
  4. Optionally cover with UV-cure solder mask or conformal coating

Pad Repair#

If a through-hole pad has lifted but the trace is intact:

  1. Glue the pad back to the board with cyanoacrylate
  2. Re-solder carefully with minimal heat
  3. If the pad is gone entirely, solder the component lead directly to the trace (scrape to expose copper first)

Jumper Wiring#

Sometimes a connection needs to be added that doesn’t exist on the board — whether for a repair, a modification, or a design fix.

Wire gauge selection:

  • Signal lines: 30 AWG wire-wrap wire (thin, easy to route, handles mA-level signals)
  • Power lines: 26–24 AWG or heavier, depending on current. Match the wire gauge to the current it will carry
  • Coax or shielded wire for sensitive signals (RF, high-speed clocks) if needed

Routing:

  • Keep jumpers short and direct
  • Secure long jumpers to the board with kapton tape or a dab of adhesive to prevent snagging
  • Route away from heat sources
  • Label the jumper (a tag of tape with a note) so the reason is clear months later

When to Stop Reworking#

Repair skill includes knowing when further attempts are about to make things worse. Every rework attempt carries risk — heat stress, lifted pads, solder bridges, damaged adjacent components — and the risk accumulates.

Pad Damage Threshold#

If two pads have lifted on the same board, stop. The cause is either too much heat, too much mechanical force, or weak copper adhesion (common in cheap or old PCBs). A third attempt at the same technique will likely lift a third pad.

Pause and reconsider:

  • Switch to a different technique (e.g., hot air instead of iron, or vice versa)
  • Lower the iron temperature and use more flux
  • Accept that the board may need jumper wires for the lifted pads before continuing
  • Consider whether the board is worth further rework or whether a fresh board is cheaper than the repair time

Thermal Collateral Damage#

Hot air is powerful but indiscriminate. Everything in the airflow path gets heated.

Plastic connectors — Most plastic housings deform or melt well below reflow temperatures. If a connector is near the rework target, either shield it with kapton tape and aluminum foil, or remove the connector first and replace it after. “I’ll be careful” is not a shielding strategy.

Adjacent components — Small passives near the target can reflow and shift, tombstone, or float away in the airflow. Shield with kapton tape, or tack them down with a dot of adhesive. After hot air rework, inspect neighbors — not just the replaced part.

Multi-layer boards — Internal copper planes act as heat sinks. The temptation is to crank the temperature to get enough heat to the target pad, but the surface temperature around the joint ends up much higher than expected. Use preheat to bring the whole board up to ~100–150°C first, so the delta from the hot air nozzle is smaller.

Diminishing Returns#

Some signs that further rework is unlikely to succeed:

  • Board is physically damaged — substrate is delaminated, charred, or warped from repeated reflow cycles
  • Multiple repairs stacked on repairs — jumper wires patching lifted pads that were damaged while replacing a component that was only suspect, not confirmed faulty
  • The replacement part is the third one tried — if the first two didn’t fix it, the component probably isn’t the problem. Go back to diagnosis
  • Working angry or tired — rework requires steady hands and patience. Frustration is a signal to walk away. The board will still be broken tomorrow, but it won’t have additional damage from a shaky hand

The cheapest rework is the one that didn’t have to be done twice.

Cleaning After Rework#

Flux residue left on the board can cause problems over time: corrosion, leakage currents, and unreliable measurement readings.

Why it matters:

  • Activated flux residue is corrosive — it was designed to dissolve oxides, and it keeps corroding copper if left in place
  • Flux residue between pads can create leakage paths, especially at higher voltages or with moisture
  • Sticky flux attracts dust and makes inspection harder

Cleaning procedure:

  1. Apply isopropyl alcohol (IPA, 90% or higher) to the rework area
  2. Scrub with a stiff brush (a toothbrush works, ESD-safe brushes are better)
  3. Wipe with a lint-free cloth or let air dry
  4. Inspect under magnification — make sure all residue is gone, especially between fine-pitch pins

No-clean flux is designed to leave benign residue, but “benign” depends on the application. For anything precision or high-impedance, clean it anyway.

Backward Diagnosing Magnetics on the Bench Verification After Repair Forward