34 www. refrigerationandaircon. co. za RACA Journal I July 2026
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7. Solder the joint
• Touch the soldering iron to the joint at an angle that maximises the surface contact to heat it. Apply the solder directly to the wire, not the iron. The solder should flow smoothly around the joint and the heat will draw the solder into the meshed strands.
• Remove the iron and allow the solder to cool naturally.
8. Inspect the joint
• A good solder joint should be shiny and smooth.
• Ensure there’ s no excess solder that could cause short circuits.
9. Shrink the tubing
• After soldering the joints, slip the heat shrinking tubing and use the heat gun to finish the process.
10. Clean and maintain your iron
• Clean the tip after use and re-tin it before turning off the iron.
HOW TO SOLDER WIRES TO CONNECTORS
• Prepare the wire ends by stripping and tinning.
• Insert the tinned wire into the connector terminal.
• Apply heat and apply solder to the point where the wire meets the connector.
For soldering wires, a general-purpose soldering iron temperature should be as below. Use lower temperatures for smaller, delicate wires and higher temperatures for thicker, higher-mass wires that absorb more heat. As a rule, aim to complete the joint within two seconds. In general, when using soldering stations one can adjust the temperature a general recommendation is as follows:
• Lead-based solder 60 / 40 or 63 / 37 Set iron to 280 – 300 ° C.
• Lead-free solder( SAC305): Set iron to 315 – 330 ° C.
SOLDERING ELECTRONICS In electronics, soldering temperature is a critical parameter. The temperature at which this soldering occurs must be carefully controlled: too low, and the solder may not fully melt or bond, leading to weak cold solder joints, too high and components, printed circuit boards, or the solder itself can be damaged( burned pads, charred flux, brittle joints, etc.). Engineers and technicians often ask what the correct soldering temperature is, but the answer depends on many factors – the solder alloy composition, the soldering method and the thermal mass of the assembly, as well as the sensitivity of components.
Achieving the right soldering temperature is crucial for strong, reliable solder joints.
• Soldering temperature directly affects joint quality and reliability. Using too low a temperature can lead to weak‘ cold’ solder joints, while too high a temperature risks damaging components or the PCB. Optimal temperature ensures proper wetting and a solid metallurgical bond.
• Different solder alloys and processes require different temperature settings. Lead-based solder melts at 183 ° C, whereas common lead-free alloys melt around 217 ° C. Leadfree soldering typically needs 30 – 50 ° C higher temperature.
• Proper soldering temperature balances fast wetting with minimal thermal stress. The soldering iron must be hot enough to melt solder quickly and flow it into joints, but not so hot that flux burns off or components overheat.
• Excessively high soldering temperatures causes flux degradation and oxidisation. Most fluxes break down above ~ 350 ° C, charring and losing effectiveness. Higher heat also accelerates solder oxidisation, which can prevent proper bonding.
• Standards and best practices guide engineers on soldering temperatures. Industry guidelines, standards and manufacturer data sheets provide temperature recommendations for various solders and processes.
Image supplied by Grant Laidlaw
Typical soldering station.
UNDERSTANDING SOLDERING TEMPERATURE AND MELTING POINT Soldering temperature is the temperature at the joint when forming a solder bond. A common misconception is that one should set a soldering iron at the solder’ s melting point. In reality, effective soldering requires the joint area to be heated above the alloy’ s melting point(‘ liquidus’). For example, a typical leaded solder( 63 % tin, 37 % lead eutectic) melts at 183 ° C, yet soldering irons are usually set much higher – often around 300 – 350 ° C – to perform good hand soldering. Similarly, lead-free solders melt around 217 ° C, but irons are set tens of degrees higher for successful soldering. There are several important reasons for this:
34 www. refrigerationandaircon. co. za RACA Journal I July 2026