Theory- 9 : - Soldering and Desoldering: Techniques

Soldering and De soldering:

Soldering is a fundamental process in electronics for joining two or more metal parts, typically on a printed circuit board (PCB), by melting a filler metal called solder into the joint. The solder, when cooled, creates a strong, durable, and electrically conductive connection. Desoldering is the reverse process, which involves removing the solder and components from a connection, enabling repairs, component replacement, or salvaging parts. Both processes are essential for electronics assembly and repair.

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Soldering: Tools, Materials, and Techniques

1. Selection and Preparation of Materials and Tools

• Solder: You must choose the right solder for your project.

  • Lead-based solder (e.g., 60% tin, 40% lead) is common and easier to work with due to its lower melting point (183∘C). However, it is toxic and its use is restricted in many countries.

  • Lead-free solder (e.g., alloys of tin, silver, and copper) is an environmentally friendly alternative, but it requires higher temperatures to melt and is slightly more difficult to use. 

    
    
    

• Flux: This is a chemical cleaning agent that removes oxides from the metal surfaces, allowing the solder to flow and bond properly. Most electronic solder comes with a flux core, which is sufficient for most applications. For more difficult joints, you can apply extra flux as a paste or liquid.

• Soldering Iron: This is the primary tool for soldering. It heats up to melt the solder.

  • Wattage: The iron's wattage determines how much heat it can generate and maintain. For delicate work on PCBs and small components, a low-wattage iron (15-30W) is sufficient. For general-purpose electronics, a medium-wattage iron (40-60W) is a good choice. High-wattage irons (80W+) are used for heavy-duty soldering on large components, connectors, and wires.

  • Tip: The tip of the soldering iron comes in various shapes, each suited for a different task.

    • Conical: A fine, pointed tip for precision work in tight spaces.

    • Chisel: A flat, broad tip that transfers heat efficiently to larger pads and components.

    • Bevel: A versatile tip that combines the features of a chisel and conical tip.

• Solder Stand: A safety-critical accessory that holds the hot iron securely when not in use. Many stands include a sponge or brass wool for cleaning the tip.

• Soldering Iron Tip Temperature: The ideal temperature depends on the type of solder and the components. For lead-based solder, a temperature of 300-350°C is common. For lead-free solder, which has a higher melting point, you'll need a temperature of 350-400°C.

2. Stages in Soldering

1. Preparation: Clean the component leads and the PCB pads to remove any dirt or oxidation.

2. Tinning the Tip: Apply a thin, even coat of solder to the clean, hot tip of the iron. This improves heat transfer and protects the tip from oxidation.

3. Heating the Joint: Place the tinned iron tip on the joint, touching both the component lead and the PCB pad. This ensures both parts are heated evenly and simultaneously.

4. Applying Solder: Once the joint is hot, touch the solder wire to the opposite side of the joint from the iron. The solder should melt and flow smoothly into the joint via capillary action.

5. Cooling and Cleaning: Remove the solder wire, then the iron. Hold the component steady for a few seconds to let the solder solidify naturally. A proper solder joint should be shiny, smooth, and shaped like a volcano. Afterward, you can clean any leftover flux with isopropyl alcohol.

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Desoldering: Tools and Techniques

Desoldering requires reheating the joint to remove the solder. There are several tools available for this process.

• Desoldering Pump (Solder Sucker): This is a manual tool that uses a spring-loaded plunger to create a vacuum, which sucks up molten solder.

  • Technique: Heat the joint with the soldering iron until the solder melts. Remove the iron, quickly place the pump's nozzle over the molten solder, and press the release button to suck the solder away.

• Desoldering Wick (Solder Braid): This is a braided copper wire coated with flux. When heated, it absorbs molten solder through capillary action.

  • Technique: Place the wick on the solder joint, then press a hot iron onto the wick. The heat melts the solder, and the wick absorbs it. Cut off the used portion of the wick after each use.

• Hot Air Rework Station: This is a more advanced tool that blows a controlled stream of hot air to melt all the solder joints of a component at once. This is the best method for removing surface-mount devices (SMD).

• De soldering Gun: A specialized tool that combines a soldering iron with a hollow tip and a built-in vacuum pump. This allows for a one-handed operation to heat and remove solder simultaneously.