Class: Senior Secondary School 1 (SS1 / SSS 1)
Term: 3rd Term
Week: 9
Age: 15 years
Duration: 45 minutes
Subject: Radio, Tv & Electronics
Curriculum Theme: Trade
Previous Lesson: Soldering And Desoldering In Electronics Circuits: Precautions And Types Of Solder.
Topic: SOLDERING AND DESOLDERING IN ELECTRONIC CIRCUITS
Subject Matter: Types of flux, Amber resin, Sodium chloride solution

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

Define flux.
List at least three types of flux.
Describe amber resin.
State why sodium chloride solution is not suitable for electronic soldering.

Affective Domain:

Appreciate the importance of using the correct flux in soldering.
Show interest in learning proper soldering techniques.

Psychomotor Domain:

Identify different types of flux materials.
Select appropriate flux for a given soldering task.

Participate in discussions about the properties of different flux types.
Collaborate in identifying safe handling practices for soldering materials.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Basic Technology.
State Unified Scheme of Work for Senior Secondary Schools.
Radio, TV & Electronics for Senior Secondary Schools by O. A. Adebayo and S. O. Eze.

Instructional Materials

The teacher will teach this lesson with the aid of:

Flux container with different types of flux (e.g., rosin, paste flux).
Solder bar/wire.
Soldering iron.
Circuit board with components.
Safety goggles.

Rationale for the Lesson

This lesson helps pupils understand the essential role of flux in creating strong and reliable electrical connections in electronic circuits. Knowing about different flux types is important for performing correct soldering and ensuring the proper functioning and longevity of electronic devices.

Prerequisite/Previous Knowledge

Pupils have a basic understanding of electronic components, the concept of soldering, and general workshop safety rules.

Lesson Content/Board Summary

SOLDERING AND DESOLDERING IN ELECTRONIC CIRCUITS

Flux

Flux is a chemical cleaning agent used in soldering to remove oxides and other impurities from the surfaces of metals to be joined. It prevents re-oxidation during the soldering process and helps the molten solder flow smoothly.

The following are the functions of flux:

It cleans the metal surfaces by removing oxides and impurities.
It prevents re-oxidation of the metal surfaces during heating.
It improves the wetting action of the solder, allowing it to flow and spread easily.
It helps in achieving a strong and reliable solder joint.

Types of Flux

Fluxes are generally categorized based on their chemical composition and activity. The following are common types of flux:

Rosin/Resin Flux (Non-acidic)
Acidic Flux
Water-Soluble Flux
No-Clean Flux

Amber Resin (Rosin Flux)

Amber resin, also known as rosin flux, is a non-acidic flux derived from pine trees. It is the most commonly used type of flux in electronics soldering.

The following are the characteristics of amber resin:

It is mildly active and non-corrosive, making it safe for electronic components.
It leaves a non-conductive and non-corrosive residue that does not usually need to be cleaned.
It provides good wetting properties for solder.

Amber resin is widely used for soldering electronic circuit boards, wires, and components where corrosion is a major concern.

Sodium Chloride Solution

Sodium chloride solution (common salt dissolved in water) is an example of an acidic flux. While some highly acidic fluxes are used in heavy-duty industrial soldering (e.g., plumbing), sodium chloride solution is generally not suitable for electronic soldering.

The following are reasons why sodium chloride solution is unsuitable for electronic soldering:

It is highly corrosive and can damage electronic components and circuit boards.
Its residue is conductive and can cause short circuits and component failure over time.
It is difficult to clean thoroughly, and any remaining residue will continue to corrode the soldered joint.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils, reviews the previous lesson briefly, and then introduces the new topic by displaying solder and a flux container. The teacher asks pupils what they think these materials are used for in electronics.
Pupils’ Activity: Pupils respond to the greetings, recall the previous lesson, and attempt to answer the teacher’s questions about the displayed materials.
Learning Point: Pupils are engaged and their prior knowledge is activated, linking to the new lesson on soldering materials.

Step 2: Presentation of Flux Definition and Importance

Time: 8 minutes
Teaching Skill: Explanation/Illustration
Teacher’s Activity: The teacher defines flux, explains its role in soldering, and lists its functions, writing key points on the board. The teacher uses diagrams or real-life examples to illustrate how flux cleans surfaces.
Pupils’ Activity: Pupils listen attentively, take notes, and ask questions for clarification regarding the definition and functions of flux.
Learning Point: Pupils understand what flux is and why it is important in the soldering process.

Step 3: Introduction to Types of Flux

Time: 7 minutes
Teaching Skill: Classification/Categorization
Teacher’s Activity: The teacher introduces the general categories of flux, such as rosin flux, acidic flux, water-soluble flux, and no-clean flux. The teacher highlights that different types are used for different applications.
Pupils’ Activity: Pupils listen, observe, and note the different types of flux as introduced by the teacher.
Learning Point: Pupils are aware that there are various types of flux with distinct characteristics.

Step 4: Detailed Explanation of Amber Resin

Time: 7 minutes
Teaching Skill: Description/Elaboration
Teacher’s Activity: The teacher focuses on amber resin (rosin flux), describing its origin, characteristics, and its common application in electronic soldering. The teacher explains why it is preferred for electronics.
Pupils’ Activity: Pupils listen, take notes, and ask questions about amber resin and its properties.
Learning Point: Pupils gain a clear understanding of amber resin as a key flux type in electronics.

Step 5: Detailed Explanation of Sodium Chloride Solution

Time: 6 minutes
Teaching Skill: Comparison/Caution
Teacher’s Activity: The teacher explains what sodium chloride solution is and specifically cautions pupils against its use in electronic soldering. The teacher states the reasons for its unsuitability, such as corrosiveness and conductive residues.
Pupils’ Activity: Pupils listen carefully, noting the dangers and unsuitability of sodium chloride solution for electronic work.
Learning Point: Pupils understand why certain substances, though technically fluxes, are harmful to electronic components.

Step 6: Class Activity/Demonstration

Time: 7 minutes
Teaching Skill: Practical Application/Demonstration
Teacher’s Activity: The teacher demonstrates how different types of flux (if available, e.g., rosin paste vs. liquid flux) are applied during soldering on a practice board. The teacher emphasizes safety precautions.
Pupils’ Activity: Pupils observe the demonstration, ask questions about the application techniques, and identify the different flux types shown.
Learning Point: Pupils observe the practical application of flux and reinforce their understanding of its use and safety.

Step 7: Evaluation/Review

Time: 5 minutes
Teaching Skill: Questioning/Assessment
Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

What is flux in the context of soldering?
Mention three functions of flux.
List two common types of flux.
Explain why amber resin is suitable for electronic soldering.
State two reasons why sodium chloride solution should not be used for electronic soldering.

Pupils’ Activity: Pupils answer orally and in writing.
Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key learning points of the lesson, reiterating the importance of selecting the correct flux for safe and effective electronic soldering. The teacher gives pupils an assignment to research other types of flux.
Pupils’ Activity: Pupils listen to the summary and note down the assignment.
Learning Point: Pupils consolidate their understanding of the lesson and are encouraged to further explore the topic.

Lesson Keywords

Flux – A chemical cleaning agent used in soldering to remove oxides and impurities from metal surfaces.
Solder – A fusible metal alloy used to create a permanent electrical or mechanical bond between electronic components.
Amber Resin – A natural, non-acidic flux derived from pine trees, commonly used in electronics.
Sodium Chloride Solution – Common salt dissolved in water; an acidic solution generally unsuitable for electronic soldering due to its corrosive nature.
Soldering – The process of joining two or more metal items by melting and putting a filler metal (solder) into the joint.
Desoldering – The process of removing solder and components from a circuit board.

Differentiation

For pupils who grasp concepts quickly, the teacher can assign additional research on advanced flux types or the chemical reactions involved in flux action. For pupils needing more support, the teacher can provide simplified diagrams and allow peer-assisted learning during the demonstration or review sections.

Note for teachers using this lesson plan

Ensure real-life examples of flux and solder are available for demonstration. Emphasize safety precautions during any practical demonstration, especially regarding fumes and hot tools. Encourage pupils to ask questions to clarify any misconceptions about flux types and their applications.