The soldering joints are between a wire and a tag, wire and circuit board pad, component lead and pad or a connector pin and pad. Most component leads/tags and wires are tin/silver plated for easy solderability. The circuit board patterns are also tin/silver plated for excellent whettability.
The wires are stripped off insulation using a wire stripper. The stripped length should be just adequate for the soldering joint to be made. Excessive length of exposed copper can cause short circuits and also the wiring joint can be easily snipped after soldering. The multi-strand wires are twisted together for mechanical integrity and solder coated before inserting into PCB/component tag holes and soldering. Component tags are also solder coated prior to soldering for ease of whettability. The wire should be bent by 90 deg. for a tag joint and by 45 deg. for a board joint. (More than 45 deg. bend for a board joint makes it difficult to repair) Soldered copper wires should not be bent at the point they emerge from soldering joint as they can be easily snipped. Wire joint should be made quickly with minimum heating to avoid damage to wire strands. Excessive solder would cause dry soldering joint and also a possible short circuit.
The resistor/capacitor component leads should not be bent closer than 1-2 mm to the components for mechanical strength. The lead bending/cutting machines are employed in electronic circuit board production. The leads of heavier components are bent with a kink for enhanced mechanical support. The solder joint should not be made closer than 3-5 mm to the components as the heat of soldering could cause damage. While soldering semiconductors/ICs, spread the heat and finish the soldering quickly to avoid overheating and possible damage/drift of component. ICs are commonly mounted on sockets for ease of dis-assembly. A grounded tip low voltage soldering iron, grounded desktop and wrist ground strap are used while soldering electrostatically sensitive devices such as MOS transistors.
While soldering components to PCB/breadboard, finish soldering quickly (2-3 sec). Excessive heat through prolonged soldering can easily cause copper foil to lift from the laminate. The components are mounted either vertically or horizontally on PCB. Vertical mounting increases component density and reduces amount of heat absorbed by the components while soldering. The horizontal mounting gives better mechanical support to components and less susceptibility to damage through vibration. The component leads are bent at 90 deg. near the components before inserting into PCB. The leads are bent at 45 deg. on solder side of PCB before soldering. The excess lead length is snipped very close to the soldering joint. The track side of assembled circuit board is cleaned off excess flux/impurities with an organic solvent.
A crimped wire connection is used as a substitute to soldering joint. This is a commonly used wire termination and is also used to connect multi-core flat cables onto crimp connectors. A wire should never be both soldered and crimped to a connector.
ANU Engineering - ENGN2211