Lesson Notes By Weeks and Term v3 - Senior Secondary 1
Soldering and Desoldering in Electronic Circuit
Download the Lessonotes Mobile Nigeria 2025 app for faster lesson access on Android and iPhone.
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 Repairs
Class: Senior Secondary 1
Term: 2nd Term
Week: 3
Theme: Workshop Practice And Maintenance
This page supports the lesson note with a companion video and a short classroom-ready summary.
For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.
Watch on YouTubeState the precautions to beobserved whilesoldering. Desoldertransistor,capacitor, and diode with outdamage. List types of solder. List types of flux.
This section provides the foundational knowledge required for effective soldering and desoldering. This section outlines practical activities for teacher-led instruction and student engagement.
Teacher Activities: Introduction (10 minutes): Begin by asking students about their experiences with faulty electronic devices (e.g., "Who has ever had a radio or TV stop working? What do you think happens inside that makes it stop?"). Introduce soldering and desoldering as essential skills for diagnosing and repairing such faults. Briefly state the objectives of the lesson. Show examples of soldered and desoldered circuit boards, faulty components, and repair work in progress (if available, e.g., a non-functional radio from the school lab). Key Concept Explanation and Demonstration (30 minutes): Safety First: Display and discuss safety precautions. Use visual aids (posters, actual safety glasses, fume extractor setup) to reinforce each point. Emphasize the dangers of lead solder fumes and burns.
Tools Introduction: Show actual soldering irons, solder pumps, solder wicks, different types of solder wire (lead-based and lead-free if available), and flux. Explain the function of each tool.
Soldering Technique Demonstration: Using a practice PCB or a scrap circuit board, the teacher demonstrates the step-by-step soldering technique for a simple resistor or capacitor. Emphasize heating both the pad and the lead, applying solder to the joint, and achieving a shiny, concave joint. Show examples of good and bad solder joints (e.g., "cold joint," "solder bridge," "insufficient solder").
Desoldering Technique Demonstration: Using a practice PCB with previously soldered components (transistor, capacitor, diode), the teacher demonstrates desoldering using both the solder pump and desoldering wick for different components. Emphasize patience, proper heat application, and clearing holes without damaging the PCB traces.
Types of Solder and Flux: Present samples of different solder types (e.g., 60/40, lead-free if possible) and discuss their characteristics. Show different flux types (if available, e.g., a flux pen or liquid flux). Explain their role in the soldering process. Practical Application Guidance (20 minutes): Divide students into small groups (if equipment allows) or conduct as a rotating station activity.
Provide each group/student with: A soldering iron, stand, damp sponge/brass wool. Solder wire (lead-based 60/40 is ideal for beginners). A solder pump and desoldering wick. A few scrap circuit boards (e.g., old radio/TV boards) or designated practice boards. Assorted through-hole components (resistors, capacitors, diodes, small transistors) for practice. Safety glasses for each student. The teacher walks around, providing individual guidance, correcting techniques, and answering questions. Emphasize starting with desoldering simpler components like resistors before moving to more sensitive components like transistors.
Student Activities: Active Listening and Observation: Students pay close attention to the teacher's explanations and demonstrations, taking notes on key concepts and safety precautions.
Tool Identification: Students identify and handle the various soldering and desoldering tools presented by the teacher, familiarizing themselves with their parts and functions.
Safety Discussion: Students participate in a brief discussion on the importance of safety, sharing potential hazards they observe.
Supervised Practical Practice: Students put on safety glasses. Students practice desoldering various components (resistors, capacitors, diodes, transistors) from the scrap/practice boards using both the solder pump and desoldering wick under the teacher's supervision. The goal is to remove the components and clear the holes without damaging the PCB or component. Students then practice soldering simple components onto new pads or empty holes on the practice board, aiming for good, shiny, concave joints. Students learn to clean the soldering iron tip regularly.
Component Identification: Students identify the types of components they are soldering/desoldering (e.g., distinguishing a capacitor from a diode by its appearance).
Reflection: Students reflect on common errors (e.g., cold joints, too much solder) and how to correct them. --- These questions help reinforce understanding and practical application, with step-by-step solutions for the teacher.
Question 1: List three essential precautions a technician must observe when soldering or desoldering an electronic circuit board.
Relevant Objective:
1. State the precautions to be observed while soldering.
Solution 1: Wear safety glasses: To protect eyes from molten solder splashes or fumes. Work in a well-ventilated area/Use a fume extractor: To avoid inhaling harmful solder fumes (especially lead-based solder). Use a soldering iron stand and avoid touching the hot tip: To prevent accidental burns. Ensure the circuit board is de-energized (unplugged and discharged): To prevent electrical shock or damage to components. Wash hands thoroughly after handling solder: To prevent ingestion of lead or other contaminants. (Teacher can accept any three relevant and distinct precautions from the list discussed).
Question 2: A technician needs to replace a faulty electrolytic capacitor on a radio receiver circuit board. Describe the step-by-step process of desoldering this capacitor using a solder pump, ensuring no damage to the board.
Relevant Objective:
2. Desolder transistor, capacitor, and diode without damage.
Solution 2: De-energize the circuit: Ensure the radio receiver is unplugged and any large capacitors are discharged.
Prepare tools: Plug in the soldering iron and allow it to heat up. Ensure the solder pump is cocked (plunger pressed).
Heat one lead: Place the hot soldering iron tip onto one solder joint of the capacitor on the solder side of the PCB, melting the solder.
Vacuum solder: While the solder is molten, quickly place the nozzle of the cocked solder pump directly over the molten solder joint and press the release button to suck the solder away.
Repeat for the second lead: Repeat steps 3 and 4 for the other lead of the capacitor.
Component removal: Once both joints are clear of solder, gently pull the capacitor out from the component side of the board. If it doesn't come out easily, check if any solder remains in the holes and repeat the desoldering process until the holes are clear.
Inspect: Check the PCB pads and traces for any damage.
Commentary: This emphasizes a practical, sequential approach to desoldering a common component, integrating safety and technique.
Question 3: A student is working on a school project and needs to join components on a circuit board. They are trying to decide between two types of solder: one clearly labeled "60/40" and another labeled "Sn96.5/Ag3.0/Cu0.5". a) Identify the type of solder for each label. b) Which type of solder typically has a lower melting point and is generally easier for beginners to work with?
Relevant Objective:
3. List types of solder.
Solution 3: a) 60/40 Solder: This is a lead-based solder, specifically containing 60% Tin and 40% Lead. Sn96.5/Ag3.0/Cu0.5 Solder: This is a lead-free solder, typically composed of Tin, Silver, and Copper. b) The 60/40 lead-based solder typically has a lower melting point (around 183-190°C) and is generally considered easier for beginners to work with due to its better flow characteristics and shinier joints compared to lead-free alternatives, which require higher temperatures.
Commentary: This question differentiates between the most common solder types and their practical implications.
Question 4: Explain the primary function of flux in the soldering process. Name two common types of flux used in electronics.
Relevant Objective:
4. List types of flux.
Solution 4: The primary function of flux in the soldering process is to clean the metal surfaces (component leads and PCB pads) by removing existing oxides and preventing new oxidation from forming during heating. This allows the molten solder to flow smoothly and create a strong, reliable electrical and mechanical connection (wetting). Two common types of flux used in electronics are: Rosin-based Flux (e.g., Rosin Activated (RA), Rosin Mildly Activated (RMA)) Water-soluble Flux (Organic Acid (OA) flux) No-Clean Flux (Teacher can accept any two of these or variations like R, RA, RMA, OA if students specify)
Commentary: This reinforces the critical role of flux and introduces common classifications. --- This section provides strategies to cater to diverse learning needs within the classroom.
A. Differentiation: The practical nature of this topic naturally lends itself to differentiation.
Visual and Kinesthetic Learners: Benefit greatly from the teacher's live demonstrations and extensive hands-on practice sessions. Step-by-step posters or laminated instruction cards at each station would be helpful.
Auditory Learners: Will benefit from clear verbal explanations during demonstrations and opportunities for discussion.
B. Remediation (for struggling learners): Individualized Demonstration: Provide one-on-one or small-group re-demonstrations of soldering and desoldering techniques, breaking down each step into smaller, more manageable actions. Increased Practice with Simpler Components: Allow struggling learners more time to practice on simple components (resistors, diodes) on scrap boards, focusing purely on achieving good joints or cleanly removing components, before moving to more complex or sensitive parts.
Visual Aids: Provide detailed, illustrated step-by-step guides or video tutorials (if resources permit) for them to follow at their own pace.
Buddy System: Pair struggling learners with more proficient students for peer support during practical sessions. The advanced student can guide and offer immediate feedback.
Focus on Key Concepts: Re-explain the basic principles of heat transfer, flux action, and good wetting using analogies or simpler terms.
C. Extension / Enrichment (for high-achieving learners): Advanced Component Handling: Challenge advanced learners to desolder and solder more complex components such as multi-pin Integrated Circuits (ICs) or components from surface-mount technology (SMT) boards (if appropriate tools like hot air stations are available and safe).
Fault Diagnosis: Provide them with circuit boards having deliberately introduced common soldering faults (e.g., cold joints, solder bridges) and task them with identifying and rectifying these faults.
Research Project: Assign a mini-research project on topics like: The environmental impact of lead-based solder vs. lead-free solder and current industry trends in Nigeria. Different types of soldering stations and their applications. Advanced desoldering techniques (e.g., using a hot air rework station for SMD components).
Mini-Design/Build Project: Encourage them to design and assemble a very simple circuit (e.g., a basic LED flasher or a continuity tester) using the soldering skills acquired, promoting critical thinking and practical application.
Tool Maintenance: Task them with learning and demonstrating proper maintenance of soldering irons, tips, and desoldering tools for the class.
This topic has direct and tangible relevance to daily life and economic opportunities in Nigeria.
Local Electronics Repair Businesses: Soldering and desoldering are core skills for technicians in local markets across Nigeria (e.g., Computer Village in Lagos, or electronics stalls in any major market). Whether it's fixing a customer's faulty mobile phone charger, a malfunctioning television, or a non-responsive radio, these skills are continuously applied to identify and replace damaged components. This directly contributes to the circular economy by extending the lifespan of electronics and reducing e-waste.
DIY and Innovation for Rural Development: In communities with limited access to new electronics, the ability to repair existing devices is vital. Individuals with soldering skills can repair crucial equipment like solar lamps, small power inverters, or agricultural electronic controls, making technology more accessible and sustainable. For instance, fixing a faulty charge controller for a solar power system in a remote village depends heavily on competent desoldering and replacement of components. Entrepreneurship in Custom Electronics/Prototyping: As Nigeria's tech ecosystem grows, there's increasing demand for individuals who can build custom electronic devices or prototypes. Students mastering soldering can venture into creating bespoke gadgets, repairing specialized industrial equipment, or even assembling small-scale electronics for local needs, such as simple security systems for homes or automated watering systems for small farms, thereby fostering local innovation and creating job opportunities. ---