Hardware Tools, Soldering, and PCB Assembly
What this domain tests
This practical domain tests workshop judgement: which tool suits which job, how a good joint differs from a cold one, and how a board is populated, inspected and reworked.
Core rules
- Soldering iron 15–30 W for PCB work; keep the tip cleaned and tinned. Solder 60/40 or lead-free at about 300–350 °C. Flux removes oxide; it is not a glue.
- Good joint: smooth, shiny, concave fillet wetting both pad and lead. Cold joint: dull, grainy, blobby, high resistance, often intermittent.
- Desoldering: add fresh solder first to improve heat transfer, then use a pump or wick.
- Never file a plated tip; wipe on a damp sponge or brass wool and re-tin immediately.
- Tools: wire stripper, flush cutter, tweezers, long-nose pliers, PCB drill, multimeter, logic probe, magnifier.
- PCB terms: pad, track, via (layer connection), silkscreen (component legend), solder mask (prevents bridges).
- Assembly order: lowest profile first (resistors, IC sockets), taller parts later. Observe polarity on electrolytics, diodes and ICs; handle CMOS with ESD precautions.
Worked example
A board fails intermittently. Inspection shows a dull, convex joint on a resistor lead. Reheat it with a clean tinned tip and a little fresh solder and flux until the solder wets both pad and lead and forms a shiny fillet, then re-check continuity with the multimeter on the appropriate range.
Traps that cost marks
Too much heat lifting pads; solder bridges between IC pins; reversed electrolytic polarity; soldering an IC directly instead of using a socket; ignoring ESD when handling CMOS.