Lesson Notes By Weeks and Term v3 - Senior Secondary 1
Soldering and Desoldering in Electronic Circuit
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Soldering and Desoldering in Electronic Circuit
Download the Lessonotes Mobile Nigeria 2025 app for faster lesson access on Android and iPhone.
Subject: Radio Television and Electrical Work
Class: Senior Secondary 1
Term: 2nd Term
Week: 3
Theme: Workshop Practices And Maintenance
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Watch on YouTubeThis topic introduces students to the fundamental skills of soldering and desoldering, which are crucial in the assembly, repair, and maintenance of electronic circuits and devices. In Nigeria, the ability to properly solder and desolder components is a highly valuable skill, essential for technicians working in electronics repair shops (e.g., GSM repair villages, TV/radio repair centres), manufacturing facilities, and even for individuals who wish to repair their own electronic gadgets. Mastering these techniques not only fosters practical skills but also opens up entrepreneurial opportunities in the rapidly growing electronics service sector.
This section provides a detailed explanation of the core concepts related to soldering and desoldering in electronic circuits. 2.
1. Definition of Soldering Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal (solder) into the joint. The solder has a lower melting point than the adjacent metal parts, which remain solid during the process. In electronics, soldering creates an electrical connection that is mechanically strong and corrosion-resistant. 2.
2. Definition of Desoldering Desoldering is the process of removing solder from an electronic joint to separate components or repair a circuit board. This is necessary when replacing faulty components, correcting errors, or salvaging parts. 2.
3. Tools and Materials for Soldering Soldering Iron: An electrical tool used to heat components and solder to the melting point.
Types: Pencil-type (common for electronics), Soldering gun (higher power, typically for heavier work), Soldering station (iron with temperature control).
Wattage: For electronics, 25W-60W irons are typically used. Higher wattage heats faster but requires more care to prevent component damage.
Solder Wire: An alloy of metals (e.g., tin and lead, or lead-free alternatives like tin, silver, copper) used as the filler material.
Flux Core: Modern solder wires often contain a rosin flux core, which helps clean the surfaces to be joined and allows the solder to flow smoothly.
Diameter: Thinner solder (0.5mm - 1.0mm) is preferred for fine electronic work.
Flux: A chemical cleaning agent that removes oxidation from the metal surfaces, allowing the solder to wet the joint effectively. Rosin flux is common for electronics. It can be in paste, liquid, or integrated into solder wire.
Soldering Iron Stand: A safe place to rest the hot soldering iron when not in use, preventing burns and protecting work surfaces.
Sponge/Brass Wool Cleaner: Used to clean the tip of the soldering iron, removing burnt flux and old solder, which ensures efficient heat transfer. A damp sponge or specialized brass wool is used.
Safety Glasses: To protect the eyes from molten solder splashes or fumes.
Fume Extractor (Optional but Recommended): A fan with a filter to remove harmful solder fumes from the workspace. 2.
4. Tools and Materials for Desoldering Desoldering Pump (Solder Sucker): A spring-loaded vacuum device used to suck molten solder away from a joint.
Desoldering Wick (Solder Braid): A braided copper wire impregnated with flux, used to absorb molten solder through capillary action.
Heat Gun (Optional): Used for desoldering surface-mount devices (SMD) or larger components requiring more heat. 2.
5. Principles of Good Soldering Cleanliness: Both the component leads and the PCB pads must be clean and free of oxidation or grease. Flux aids this.
Heat Transfer: The soldering iron tip must be clean and tinned to transfer heat efficiently to both the component lead and the PCB pad simultaneously.
Wetting: The solder must flow smoothly and evenly, forming a concave fillet (like a volcano shape) around the joint, indicating a good bond. It should look shiny.
Minimal Heat Exposure: Components can be damaged by excessive heat. Heat the joint only long enough for the solder to flow, then remove the iron. 2.
6. Step-by-Step Soldering Procedure
1. Preparation: Plug in the soldering iron and allow it to heat up (usually 2-5 minutes).
Clean the soldering iron tip: Wipe it on a damp sponge or rub it against brass wool.
Tin the Tip: Apply a small amount of fresh solder to the clean tip. This protects the tip from oxidation and improves heat transfer. Place the component into the correct holes on the PCB. Bend leads slightly to secure it if necessary. Ensure proper ventilation and wear safety glasses.
2. Heating the Joint: Place the clean, tinned soldering iron tip so it touches both the component lead and the PCB pad simultaneously. Heat for 2-4 seconds. The goal is to bring both surfaces to the solder's melting temperature.
3. Applying Solder: * While keeping the iron tip in place, touch the solder wire to the opposite side of the heated joint (not directly to the iron tip). into the correct holes on the PCB. Bend leads slightly to secure it if necessary. Ensure proper ventilation and wear safety glasses.
2. Heating the Joint: Place the clean, tinned soldering iron tip so it touches both the component lead and the PCB pad simultaneously. Heat for 2-4 seconds. The goal is to bring both surfaces to the solder's melting temperature.
3. Applying Solder: While keeping the iron tip in place, touch the solder wire to the opposite side of the heated joint (not directly to the iron tip). The solder should flow into the joint, not melt on the iron. Apply just enough solder to form a shiny, concave cone-shaped joint, ensuring the component lead and pad are completely covered and connected. Avoid excessive solder.
4. Removing Solder and Iron: First, remove the solder wire. Immediately after, remove the soldering iron. Do not move the component for a few seconds while the solder cools and solidifies.
5. Inspection and Finishing: Inspect the joint: It should be shiny, smooth, concave, and cover both the lead and the pad. Trim any excess component lead using side cutters (flush cutters) close to the solder joint. Clean any flux residue with an appropriate solvent (e.g., isopropyl alcohol) if necessary, using a small brush or cotton swab. 2.
7. Step-by-Step Desoldering Procedure Method 1: Using a Desoldering Pump
1. Preparation: Heat the soldering iron. Ensure the desoldering pump is charged (plunger pushed down and locked). Wear safety glasses.
2. Melt the Solder: Place the soldering iron tip onto the solder joint to melt it.
3. Position and Actuate Pump: As soon as the solder becomes molten, quickly remove the iron and position the nozzle of the desoldering pump directly over the molten solder. Press the release button to activate the vacuum, sucking the molten solder into the pump.
4. Repeat if Necessary: If all solder is not removed, repeat the process. Ensure the pump is clean and free of old solder.
5. Remove Component: Once most of the solder is removed, gently wiggle and pull the component out. If it resists, reheat and remove any remaining solder.
Method 2: Using Desoldering Wick (Solder Braid)
1. Preparation: Heat the soldering iron. Unroll a small length of desoldering wick. Wear safety glasses.
2. Position Wick and Iron: Place the desoldering wick directly over the solder joint to be desoldered. Place the hot soldering iron tip directly onto the wick, pressing it down onto the solder joint.
3. Absorb Solder: The heat will transfer through the wick to the solder, melting it. The molten solder will then be drawn into the wick by capillary action. Move the wick slowly over the joint until all the solder is absorbed, or use fresh sections of wick as it saturates with solder.
4. Remove Wick and Iron: Once the solder is absorbed, remove the soldering iron and then the wick. Cut off the used (solder-saturated) portion of the wick.
5. Remove Component: Gently wiggle and pull the component out. Reheat and use more wick if necessary. 2.
8. Safety Precautions in Soldering and Desoldering Eye Protection: Always wear safety glasses to protect against molten solder splashes.
Ventilation: Work in a well-ventilated area or use a fume extractor to avoid inhaling harmful solder fumes (especially lead-based solder).
Burn Prevention: Always place the hot soldering iron in its stand when not in use. Avoid touching the hot tip or barrel of the iron. Be aware of hot components and solder.
Electrical Safety: Ensure the soldering iron cable is in good condition. Never touch live electrical circuits while soldering. Disconnect power.
Tool Handling: Use tools correctly and store them safely. Cut leads away from the body.
Lead Poisoning (if using leaded solder): Wash hands thoroughly after handling solder and before eating or drinking.
Component Care: Be mindful of static electricity (use anti-static mats/wrist straps for sensitive components) and heat damage. 2.
9. Common Soldering Faults and Troubleshooting * the iron. Be aware of hot components and solder.
Electrical Safety: Ensure the soldering iron cable is in good condition. Never touch live electrical circuits while soldering. Disconnect power.
Tool Handling: Use tools correctly and store them safely. Cut leads away from the body.
Lead Poisoning (if using leaded solder): Wash hands thoroughly after handling solder and before eating or drinking.
Component Care: Be mindful of static electricity (use anti-static mats/wrist straps for sensitive components) and heat damage. 2.
9. Common Soldering Faults and Troubleshooting Cold Joint (Dry Joint): Appearance: Dull, grey, granular, or cracked appearance; often appears like a ball on top of the pad, not flowing smoothly.
Cause: Insufficient heat, movement during cooling, or dirty surfaces.
Effect: Intermittent or no electrical connection, poor mechanical strength.
Remedy: Reheat the joint, ensuring proper heat transfer and applying a small amount of fresh solder/flux if needed, and allow it to cool undisturbed.
Solder Bridge: Appearance: Solder inadvertently connects two or more adjacent pads/leads that should be separate.
Cause: Too much solder, accidental contact between leads, or improper iron technique.
Effect: Short circuit, device malfunction.
Remedy: Melt the bridge with the soldering iron and carefully drag the excess solder away or use a desoldering pump/wick to remove it.
Excess Solder: Appearance: A large blob of solder covering the joint, making it difficult to inspect or potentially creating bridges.
Cause: Applying too much solder.
Effect: Potential for cold joints, solder bridges, wasted solder.
Remedy: Remove excess solder using a desoldering pump or wick.
Insufficient Solder: Appearance: The joint looks incomplete, showing exposed lead or pad, not fully concave.
Cause: Not enough solder applied.
Effect: Weak mechanical connection, poor electrical conductivity.
Remedy: Reheat the joint and add a small amount of fresh solder.
Lifted Pad/Track: Appearance: A copper pad or trace on the PCB detaches from the board.
Cause: Excessive heat, prolonged heating, or aggressive component removal.
Effect: Open circuit, irreparable damage to the PC
B. Remedy: Difficult to repair. Can sometimes be fixed by scraping off solder mask to expose the track and bridging with a wire, but often means replacing the PC
B. Emphasize prevention.
Phase 1: Introduction and Explanation (40 minutes)
Teacher Activity: Introduce the topic "Soldering and Desoldering in Electronic Circuit" and its relevance, drawing on examples of faulty electronic devices common in Nigerian households (e.g., non-functional radio, TV, phone charger, fan regulator). Display and identify actual soldering and desoldering tools and materials (if available). If not, use detailed diagrams or pictures. Explain the function of each tool (soldering iron, solder, flux, desoldering pump, wick, stand, safety glasses). Define soldering and desoldering, emphasizing the principles of good soldering. Demonstrate the proper procedure for tinning a soldering iron tip and cleaning it. Highlight safety precautions, explaining potential hazards (burns, fumes, electrical shock) and how to mitigate them.
Student Activity: Participate in a brief discussion on experiences with faulty electronics and the need for repair skills. Observe the teacher's demonstration of tools and tinning. Take notes on definitions, tools, and safety precautions. Ask clarifying questions regarding tool identification and usage.
Phase 2: Step-by-Step Procedure and Practical Demonstration (60 minutes)
Teacher Activity: Explain the detailed step-by-step procedure for soldering, breaking it down into manageable parts (preparation, heating, applying solder, removing, inspection). Perform a live demonstration of soldering a simple component (e.g., a resistor or LED) onto a practice PCB or perfboard. Emphasize the "clean, heat, apply, remove, inspect" mantra. Explain the detailed step-by-step procedure for desoldering using both the desoldering pump and desoldering wick. Perform a live demonstration of desoldering the previously soldered component using both methods. Show examples of good solder joints versus common faults (cold joints, solder bridges, excess solder) using prepared samples or diagrams, explaining troubleshooting.
Student Activity: Observe the teacher's soldering demonstration keenly, noting each step. Observe the teacher's desoldering demonstrations for both methods. Draw diagrams of a good solder joint and common faulty joints in their notebooks. Engage in Q&A regarding the procedures and common faults. Form small groups to discuss observed techniques and identify potential pitfalls.
Phase 3: Guided Practical Session / Group Work (If resources permit) (60 minutes)
Teacher Activity: Organize students into groups (if resources allow for multiple soldering stations). Distribute practice PCBs, components, soldering irons, solder, and desoldering tools to each group. Supervise students closely, providing individual guidance, correction, and feedback. Continuously reinforce safety protocols. Circulate to observe student techniques and address difficulties. For classrooms with limited practical resources, the teacher can assign tasks like: Drawing detailed step-by-step diagrams of soldering/desoldering. Role-playing the soldering/desoldering process, mimicking the tool handling. Identifying faulty solder joints from various photographic examples.
Student Activity: (Practical option): Under supervision, students will practice soldering and desoldering components on practice boards. They will focus on creating clean, shiny, concave joints and effectively removing solder. (Limited resource option): Students will engage in group discussions, draw detailed procedural diagrams, or analyze images of good and bad solder joints, articulating the characteristics of each. Students will practice identifying and describing safety measures.
Phase 4: Review and Assessment (20 minutes)
Teacher Activity: Review key concepts, procedures, and safety measures. Lead a quick Q&A session. Provide feedback on practical work (if done) or theoretical understanding. Administer a short quiz or ask assessment questions.
Student Activity: Participate in the review session. Answer assessment questions individually. Clarify any remaining doubts.
Local Electronics Repair and Maintenance (GSM Villages, TV/Radio Repair Shops): Application: In Nigeria, the demand for electronics repair is high due to cost of new devices and frequent power fluctuations. Skills in soldering and desoldering are fundamental for repairing common faults in mobile phones (e.g., charging port replacement, speaker/microphone repair), television sets (e.g., replacing faulty capacitors, power supply repairs), radios, and other household appliances. Many enterprising young Nigerians establish small repair businesses (like those found in "GSM Villages" or local markets) using these very skills.
Integration: Students can visit a local electronics repair shop to observe technicians at work, identifying tools and techniques used. They can also bring in simple faulty electronic items from home (e.g., an old radio) for a practical class demonstration (under strict supervision) if resources allow. Small-Scale Electronics Assembly and Prototyping (Innovation Hubs, Tech Start-ups): Application: With the rise of local tech innovation and start-ups in Nigeria, there's a growing need for individuals who can assemble electronic prototypes or conduct small-batch manufacturing. This includes assembling custom PCBs for educational projects, security systems, smart home devices, or agricultural monitoring tools. Soldering skills are indispensable for bringing these designs to life.
Integration: Students can be challenged to design a simple circuit (e.g., an LED flasher, a simple alarm) on a breadboard, then (if resources permit) transfer the design to a perfboard or custom PCB, soldering the components themselves. This connects theoretical knowledge with practical application in product development. Self-Reliance and Cost Saving in Households: Application: Families in Nigeria often face challenges with faulty electronics. Knowing how to troubleshoot simple issues and perform basic soldering can save money by repairing items instead of replacing them. For example, fixing a loose wire in a fan or a broken charging cable can extend the life of household items and reduce waste.
Integration: Encourage students to identify common electronic items in their homes that could potentially be repaired with basic soldering skills (e.g., toys, remote controls, simple chargers). This fosters a sense of self-reliance and practical problem-solving.