Soldering, Desoldering and PCB Rework
What this domain tests
Soldering, Desoldering and PCB Rework tests hand soldering, hot-air work, wick/flux use and damage avoidance on small pads and connectors.
Core rules
- Tin the iron tip, keep it clean, and use flux for every joint. Lead-free solder typically needs 350–380 °C; use the lowest effective temperature and short contact.
- Heat the pad and lead together, feed solder, then remove solder and iron. A good joint is shiny and concave, not a ball.
- For desoldering, add fresh solder and flux, then use wick or hot air. Hot air for small SMD parts is often 330–380 °C with low airflow and a preheated board.
- Support connectors and protect nearby plastic with heat-resistant tape. Never lever a pad; lift components when solder is molten.
- Clean flux residue, inspect under magnification, and check for bridges with continuity.
Worked example
Replace a micro-USB charging port. Apply flux, remove old solder with wick, and heat the shield tabs with hot air while supporting the connector. Clean the pads, align the new port, solder the shield tabs first for mechanical strength, then the pins. Check each pin to its neighbour for shorts and to its trace for continuity. Power the board on a current-limited supply and confirm charging current. The reasoning: shield tabs carry mechanical load, and testing before assembly catches bridges that could short VBUS.
Traps
Too much heat lifts pads; no flux causes cold joints; dragging a hot iron across fine pins bridges them; wick held too long overheats the board; failing to clean flux hides corrosion.