Practical - 11 :- Soldering Resistors on a Printed Circuit Board (PCB)

AIM :- Soldering Resistors on a Printed Circuit Board (PCB)

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Objective 🎯

To learn and practice the skill of soldering resistors correctly and safely onto a general-purpose PCB.

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Materials and Equipment 🛠️

Tools & Instruments:

• Trainee's Toolkit (including wire cutters/strippers)

• Soldering Iron (25W)

• Soldering Iron Stand

• Soldering Tip Cleaning Sponge (dampened)

• Cleaning Brush (stiff, like a toothbrush)

Materials & Components:

• General Purpose PCB

• Resistors (quantity as required)

• Solder Wire (60/40 Grade)

• Flux

• Isopropyl Alcohol (IPA) Solution for cleaning

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Safety Precautions ⚠️

• HOT IRON: The soldering iron reaches very high temperatures. Always place it in the stand when not in use. Never touch the metal tip.

• AVOID OVERHEATING: Do not hold the iron on the PCB pad for more than 2-3 seconds. Overheating can permanently damage the copper track, causing it to peel off the board.

• PREVENT SHORT CIRCUITS: Use only a small amount of solder. Excessive solder can flow and accidentally connect two separate pads (a "solder bridge"), causing a short circuit.

• VENTILATION: Work in a well-ventilated area to avoid inhaling fumes from the melting flux.

• EYE PROTECTION: It is advisable to wear safety glasses.

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Procedure ⚙️ 

Step 1: Preparation

1. Inspect the PCB: Check both the component side and the copper side of the board to ensure it is clean and undamaged.

2. Prepare the Resistors: Bend the leads (pins) of each resistor at a 90° angle so they can be easily inserted into the holes on the PCB.

Step 2: Component Placement 3. Plan the Layout: Decide where you will place the resistors on the PCB. 4. Insert the Resistors: Push the resistor leads through the designated holes from the component side (the side without copper tracks). Press the resistor so it sits flat against the board. 5. Secure the Component: Turn the PCB over. Bend the leads outwards at a slight angle to hold the resistor in place so it doesn't fall out during soldering.

Step 3: Soldering 6. Heat the Iron: Turn on the soldering iron and let it reach the proper temperature. Clean the hot tip on the damp sponge. 7. Apply Flux: Apply a small amount of flux to the point where the resistor lead meets the copper pad on the PCB. 8. Heat the Joint: Touch the tip of the hot soldering iron to both the resistor lead and the copper pad simultaneously. 9. Apply Solder: Hold the iron in place for 1-2 seconds, then bring the tip of the solder wire to the heated joint (touch the lead and pad, not the iron). It should melt and flow smoothly, forming a neat, volcano-shaped connection. 10. Remove Iron: Remove the solder wire first, and then immediately remove the soldering iron. 11. Repeat: Solder the other pins of the resistors in the same manner.

Step 4: Finishing and Inspection 12. Trim Excess Leads: After the solder joints have cooled, use a wire cutter to trim the excess length of the resistor leads as close to the joint as possible. 13. Clean the Board: Pour a small amount of IPA solution onto the soldered area and use the cleaning brush to scrub away any leftover flux residue. This prevents corrosion and allows for a clear inspection. 14. Final Check: Inspect your work. A good solder joint should be shiny and cone-shaped. Ensure there are no solder bridges between pads. Have your instructor review your completed work.