Trade Practice and Workshop Skills
Trade Practice and Workshop Skills
This domain assesses hands-on competence: soldering and desoldering, PCB work, correct use of hand tools, wiring practice, and designing for maintainability.
Core rules
- Solder: 60/40 tin-lead melts near 183 °C; lead-free SAC305 needs about 217 °C and a hotter tip. Use rosin flux for electronics - never acid flux, which corrodes joints.
- Tip temperature 300–350 °C for leaded work: heat pad and lead together, feed solder into the joint, withdraw, and let it cool undisturbed. A good joint is bright and concave; a cold joint is dull, grainy and intermittent.
- Heat-shunt sensitive devices and keep dwell time short. Remove solder with a pump or wick without lifting pads.
- PCB work: track width adequate for the current, clean copper, ferric chloride etchant, drill on centre, inspect for bridges and cold joints before power-up.
- Tools: side cutters for leads, long-nose pliers for bending, wire strippers sized to the conductor, crimping tool for lugs; never misuse a tool for a job it was not made for.
- Wiring practice: strip only what is needed, form a clockwise loop under the screw, use the correct terminal, fit grommets at cable entries, label cores.
- Maintainability: accessible mounting, connectors and modular sub-assemblies, drawings and spare lists, preventive maintenance schedule.
Worked example
An intermittent fault traces to a dull, grainy joint on a PCB pad. Procedure: isolate and discharge, remove old solder with wick and rosin flux, clean the pad, tin iron and pad, reheat pad and lead together for 2–3 s, feed fresh solder, remove the iron, hold still until set, then inspect and test continuity. The reasoning: the original joint was flux-starved and heated unevenly, so the alloy never wetted the pad.
Mark-losing traps
- Moving the joint while it solidifies, creating a cold joint.
- Using excess solder that bridges adjacent pads.
- Overheating until pads lift or semiconductors fail.