Experimnet - 9 :- Soldering and De soldering on a PCB

 Aim : Soldering and De soldering on a PCB

This experiment is designed to give you hands-on experience with the fundamental skills of soldering and de soldering through-hole components on a Printed Circuit Board (PCB).

Required Materials & Equipment

• Soldering Station: A soldering iron with a stand and tip cleaner (wet sponge or brass wool).

• Solder: Rosin-core solder wire (e.g., 60/40 tin-lead or lead-free).

• PCB: A simple, single-sided PCB with pre-drilled holes for components. A "practice kit" or a generic prototype board works well.

• Components: A few basic through-hole components like resistors, diodes, and capacitors.

• De soldering Tools: A de soldering pump ("solder sucker") and de soldering wick (braid).

• Safety Glasses: Mandatory for eye protection.

• Wire Cutters: To trim component leads.

• Pliers or Tweezers: To hold components or wires.

• Fume Extractor (Recommended): To vent solder fumes.

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Procedure

Part 1: Soldering 

1. Preparation:

   • Set up your workstation in a well-ventilated area.

   • Wear your safety glasses.

   • Plug in the soldering iron and allow it to heat up to the recommended temperature for your solder (typically 350-400°C for lead-free solder).

   • Tin the iron tip: Apply a small amount of solder to the tip. This makes heat transfer more efficient. Wipe the excess on the tip cleaner.

2. Component Placement:

   • Identify the designated locations on the PCB for each component.

   • Insert the leads of a component (e.g., a resistor) through the correct holes.

   • Bend the leads slightly on the back of the board to hold the component in place while you solder.

     
     
     

3. Soldering the Joint:

   
   
   

   • Hold the soldering iron like a pen.

   • Simultaneously touch the hot iron tip to the component lead and the copper pad on the PCB. Heat both surfaces for 2-4 seconds.

   • Touch the solder wire to the opposite side of the heated joint, away from the iron. The solder should melt and flow evenly, forming a shiny, concave fillet around the lead.

   • Remove the solder wire first, then the iron.

   • Let the joint cool naturally. Do not blow on it or move the component.

4. Inspection and Finishing:

   • Visually inspect the joint. A good joint should be shiny, smooth, and have a "volcano" or "fillet" shape. A dull, grainy, or lumpy joint is a cold joint and indicates insufficient heat.

   • Use wire cutters to trim the excess component lead close to the solder joint.

Part 2: De soldering

1. Using a De soldering Pump:

   
   
   

   • Heat the soldered joint until the solder becomes molten.

   • Cock the plunger of the de soldering pump.

   • Quickly remove the soldering iron and place the tip of the pump over the molten solder.

   • Press the release button to activate the vacuum, which will suck the molten solder into the pump.

   • Repeat this process until most of the solder is removed. The component should now be loose and easily removable.

2. Using a De soldering Wick:

   
   
   

   • Place the de soldering wick on the soldered joint.

   • Place the hot soldering iron tip on top of the wick, pressing it against the joint.

   • The solder will melt and be drawn up into the copper wick through capillary action.

   • Remove the iron and the wick simultaneously.

   • Snip off the used section of the wick and discard it.

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Key Concepts for Analysis

• Heat Transfer: A good solder joint relies on efficient heat transfer from the iron to both the component lead and the PCB pad. The solder melts only when these parts are hot enough.

• Wetting: This is the process where molten solder flows and adheres to the metal surfaces, forming a strong bond. It is essential for a good connection and is aided by flux.

• Cold Joint: A dull, lumpy joint that looks grainy is a cold joint. It has poor electrical and mechanical connections due to insufficient heat.

• Solder Bridge: An unwanted connection between two nearby pads or traces, often caused by too much solder.

• PCB Damage: Excessive heat can cause the copper pads or traces to "lift" from the board, permanently damaging it.

• Polarity: For components like diodes and polarized capacitors, correct orientation is critical. Ensure the component's positive and negative terminals (anode and cathode) align with the markings on the PCB.