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Introduction to Circuit Assemblies

The process of learning about circuits and learning how to assemble them is quite easy. Therefore, this guide will be of immense help to a beginner in circuit assembly. We will discuss the basics of electricity and how it relates to a circuit and we will also touch on the materials needed to assemble a circuit. This foundational knowledge will give you an edge when you progress to much more advanced stuff.

What is Circuit Card Assembly?

Circuit card assembly involves several stages. Circuit card assemblies are the complete PCB after the assembling of every component. A printed circuit board has no electrical components. Circuit card assemblies are the complete board assembly. The assembling of a circuit board requires both active and passive components.

Circuit card assembly is also the same as printed circuit board assembly. These terminologies are widely used in the PCB industry. The process of circuit card assembly involves several stages.  Circuit card assemblies involve using schematic capture tools or CAD software.

Circuit card assembly involves connecting the wirings of PCBs with the electronic components. The traces in the copper sheets of PCBs will form the assembly.

Ways to Create Circuit Card Assemblies

circuit assembly

There are several ways to create circuit assemblies. So, it is important one pays attention to details during the process of circuit card assemblies.

Plated through-hole technology

This method involves mounting the components on the circuit board by putting their leads via the respective hole. The circuit board already has drilled holes. This makes it easy to assemble the circuit boards with the components. A thin layer of copper covers the holes’ inner wall. With this, the whole area of the inner hole becomes conductive.

This method has its benefits and disadvantages. PTH might fail due to the cracks in the copper that plates the inner hole. There are ways of testing the reliability of PTH.

Surface mount technology

Surface mount technology is a common way of creating card assemblies. This method is mostly preferred in the PCB industry. Most circuit card assembly manufacturers prefer SMT due to the benefits it offers.  SMT refers to the process of using automated machines to assemble electronic components on a circuit board.

Electro-mechanical assembly

This method utilizes cable assembly, molded plastics, wire harnesses, and looms. These things help to assemble electronic components on a PCB. Effective circuit assemblies help to ensure the smooth function of electronic devices.

Steps in Circuit Card Assembly

Printed circuit boards have been the backbone of most electronics devices. These boards offer connectivity for the components of an electronic device. A circuit card assembler ensures that the circuit board is properly assembled. Circuit card assembly involves step by step process to achieve. However, this step may vary based on the method of PCB assemblies.

Schematic design

This is an important stage in circuit card assembly. You should design a schematic that serves as a guideline for the whole circuitry. A schematic is a roadmap that features symbols that represent the entire circuit board. As a circuit card assembler, you should create a schematic. This will help you tackle any problem that may arise in the future.

Board design layout

After creating the schematic, the next thing is to lay out the board design. This involves translating the schematic into design software. The assembler will then export it into an acceptable format. This format will help the production stage of the circuit board.

Manufacturing & Assembling the PCB

This stage involves creating the board. In circuit card assembly, there are different methods. An assembler can either use plated through-hole technology or surface mount technology. The choice of method to use depends on the board’s specific requirements.

Inspection and testing

This is the last stage of the assembly process. It is important you test the circuit board to ensure it works perfectly. There are three different methods of inspecting circuit boards.  Visual inspection, X-ray inspection, and Automatic optical inspection are these methods. These methods have a similar purpose but use different ways to carry out inspection.

The visual inspection only inspects the soldered connections. The AOI machine uses high-resolution cameras to test circuit boards. For complex PCBs, an X-ray inspection will take place.

Circuit Assembly Design Basics

All electronic devices feature circuit assembly. Even the smallest electronic device has circuit assembly. It is important we understand the basics of circuit assembly design. Irrespective of the type of circuit board, all circuit boards feature the layers below;


 This is the foundational material for circuit assembly. The substrate provides the circuit board with rigidity. Fiberglass is the primary material for the substrate layer of any circuit board. Asides from flexible PCBs, most boards use fiberglass for their substrate.


Printed circuit boards feature a layer of copper foil. The manufacturer laminates the copper foil to the board using heat. The number of copper layers for a PCB depends on the type of PCBs. For example, single-sided PCBs require a layer of copper on one side of the board.

Solder mask
The yellow or green color of circuit boards is a result of soldermask. The manufacturer places the soldermask on top of the circuit board. This helps to insulate the copper layer. Doing this will prevent the copper from any contact with other metals on the board. The soldermask layer helps the manufacturer to solder the components to the appropriate places.


The silkscreen is the final and uppermost layer of all circuit boards. This layer features components in symbolic or textual form. It helps engineers to have a better understanding of the board. The silkscreen adds symbols, letters, and numbers to the board. This helps to understand the functions of various LEDs and pins.

Manufacturing Steps of Circuit Card Assembly

circuit card assemblies

A circuit card assembly involves several steps.

Solder paste stenciling

The CCA manufacturer applies a solder paste to the circuit. This process involves applying solder paste on specific portions of the board. This portion holds several electrical components. Various tiny metal balls make up the solder paste. Tin accounts for 96.5 percent of the solder paste. Other substances used for solder paste include copper and silver.

The manufacturer must apply the right amount of solder paste at the appropriate spots. You can utilize various applicators to spread paste in the right locations.

Pick and place

The pick and place process involves using an automated machine. Here, the manufacturer puts various SMDs and electronic components on the PCB. You can pick and place components on circuit boards using either automated or traditional methods. Manufacturers place components on boards using a pair of tweezers in the traditional method. In the automated method, manufacturers use machines.

Reflow soldering

Manufacturers need to solidify the solder paste after the components have been rightly placed. In this process, the boards get to a conveyor belt. This belt passes from a large reflow oven. This oven features heathers with various temperatures.  The heathers change the solder into a paste using heat. The conveyor belt goes through coolers. This will help to solidify the solder paste. This process enables all components to be firm on the board.

Quality control

This is stage is very important. Manufacturers have to check the board for any errors after they have mounted the components. Here, manufacturers inspect the board’s functionalities. Some boards are poorly connected during the reflow process. Therefore, there can be some connection problems in these boards. It is important to inspect the board for any errors.

What is a Circuit?

First, let’s discuss the way electric current works. Electricity needs to flow before it can perform any activity. Electricity cannot flow through all types of materials. It can only flow through certain materials that can conduct it. An example of this is copper wire.

Electricity automatically flows from a point of high voltage to a point of low voltage. Once you put a conductive route from a high voltage to a low voltage electric currents can flow on that route. You can test if the route is flowing with electricity by inserting an LED to serve as a load. The electricity should light up the LED.

Electricity has two poles or sides. This is commonly found on batteries and some sockets with two or more holes. These poles are usually called terminals. They are negative (-) and positive (+).  The purpose of these two different poles is to create a point of high voltage and a point of low voltage for electric current to flow

As such, in any electric current transmission, the positive pole has a higher current than the negative pole. The volts in the negative pole are often zero and the positive pole contains as many volts or current as it needs to supply. This explains how an electricity source works. For instance, generators and batteries generate electricity and transmit it towards the positive side. The negative side then sucks in electric current back to keep the electricity flowing and active.

This path through which electric current moves back and forth is what a circuit is. A circuit could be very simple like connecting a Light Emitting Diode to both poles of a battery.

Components of an Electric Circuit and Network

These are the main components of an electric circuit:

  • Node: A node is a junction or point where at least two circuits elements (capacitors, resistors, inductors, and so on) meet.
  • Branch: A branch is the section of the circuit amid two junctions. In a branch, you can join one element or even more and there will be two terminals.
  • Loop: A loop is a path in a circuit that contains more than two meshes. It is the enclosed path of a circuit. Thus, a loop can contain meshes, but a mesh cannot contain another loop.
  • Mesh: A mesh is like a loop but it does not contain another loop.

Basic Electronic Components that are necessary for circuit assembly


There are some rudimentary electronic components that you will make use of when assembling electronic circuits. Some of these components are diodes, integrated circuits, transistors, capacitors, and resistors. We will briefly examine the functions and uses of these electronic components.


A resistor is a major component used in the circuit assembly.

A resistor as the name suggests adds resistance to the electric current flowing in a circuit. Resistors represent a different value that reflects with a color code. The unit of resistance is Ohms and Omega is its symbol.

When you draw a circuit on paper, the resistor is symbolized with a pointy squiggle that has a value written beside it.

You can measure the resistance level of a resistor. You can use a Graphical Resistance Calculator to measure it. Each resistor usually has a different wattage rating. You will find one-quarter watt resistors in DC circuits.


A diode is a polarized component. The electricity in a diode flows in one direction. This offers an advantage if you want electric current in a circuit to flow in a particular direction.

A ring on the diode is a symbol that indicates that one side is connected to a GND (Cathode) and the other terminal side is connected to Power (Anode) or VCC.


A transistor is a component that receives a small amount of electric current at its base pin and augments the current to the extent that a larger current can flow between its emitter pins and collector. The electric current that flows through the two pins is proportionate to the number of volts that are applied to the base pin. These perform the role of a switch that does not have a moving part. A microcontroller can be used to control this.

There are various kinds of transistors. PNP, MOSFETS, and NPN are some common examples of transistors.

There are three parts of a transistor. The first is the Base. The base serves as the lead which is used to activate the transistor. The second and third are the collector and emitter. The collector serves as the positive lead while the emitter serves as the negative lead.


A potentiometer is a type of resistor which can vary. A slider or a knob can vary the resistance. These mechanisms are usually employed to regulate the brightness and volume of lights. Knob potentiometers and slider potentiometers are similar to transistors. A potentiometer has three terminals.

Integrated Circuit (IC)

This is also called a microchip. An IC can be described as a largely diminutive form of a very large circuit. It contains millions of tiny transistors and resistors. It receives input and gives out output through the several terminals the IC has. To understand how a specific IC operates, you can look up its datasheet.  

There is no specific design for an integrated circuit. It can be made into several sizes and shapes. Beginners will be more involved with DIP chips. These chips are built with a pin for through-hole soldering. SMT (Surface Mount Technology) chips are used in the more advanced electronic circuit assembly.

Light Emitting Diode (LED)

An LED is a device that converts electricity into light. A light-emitting diode is also a semiconductor. It is more durable when compared to an incandescent light bulb. An LED is not restricted to a kind of color. They are very efficient and they produce more light from the electric energy and little heat.

If you want to power several LEDs in a circuit, use the parallel circuit method. As tempted as you may be, do not wire them in series. This is because the voltage will keep dropping after it reaches each of the LEDs until the electric current left is insufficient to sustain the lit LEDs. If you use the parallel circuit method, make sure the LEDs you use all have equal power ratings. This is because the ratings vary with the color.


A switch simply refers to a device that breaks a circuit mechanically. When you trigger a switch, it either closes the circuit or opens the circuit. This depends on the kind of switch in the circuit. The switch that opens or closes a circuit is the simplest form. Advanced switches will perform the function of opening a connection while simultaneously closing another when you activate the switch. This advanced type of switch is a single-pole-double-throw switch (SPDT).

There are several varieties of switches which include SPCO, SPST, 2P6T, or DPDT and DPST.


A battery helps to convert chemical energy into electrical energy. A battery contains specific chemicals that react with each other in a particular way to create electricity. Every battery has three parts, the cathode (+ positive side), the anode (- negative side), and an electrolyte. You connect the anode and cathode to an electric circuit.

The reactions of the chemicals in the battery lead to an accumulation of electrons at the anode. This makes the voltage at the anode high and the voltage at the cathode at zero. Thus the electrons will flow from a high voltage point to a low voltage point. That is from the anode to the cathode.

Batteries are symbolized in a circuit diagram by lines of dissimilar lengths that are serially arranged. There are further markings that can be attached to the symbol to signify ground, voltage rating, and power.


This component can test and design circuits. Breadboards are commonly used by engineers. When using a breadboard, there is no need for you to solder components and wires to construct a circuit. A breadboard makes it convenient to mount and reuse components. Also, since the components are not fixed through soldering you can easily maneuver the design of your circuit at any point during assembly.

Breadboards contain a collection of conductive metal clips enclosed inside a white plastic box.  The plastic box has several holes that are specifically arranged. The average breadbox layout consist of two kinds of a region known as strips. They are socket strips and bus strips. The bus strips often serve as a means of power supply for the circuit. There are two columns in bus strips, one column for ground and the other for power voltage.


Just as you would use a tape rule to measure cloth, a ruler to measure length, or a watch to measure time, this is an easily accessible tool that can measure electric energy or electricity. A multimeter can measure a lot of things apart from electricity. It usually has a knob that you can use to choose the type of measurement you want.  

Platforms Useful for Assembling Circuits


The Arduino platform is an open-source program that assembles circuits and build electronic projects. This platform has a microcontroller (a microcontroller is a tangible programmable circuit board) and software you can run on your PC. This software is for the purpose of writing and uploading computer code to the microcontroller.

Autodesk 123D

The best way to get started with Arduino is to write a simple project and figure out the right code to run with it. If the Arduino platform is inaccessible for you and you want a quicker way to assemble a circuit or you want to expand your horizon and learn other methods, you can give 123D circuits a try.

123D Circuit is an online platform that allows you to construct and test run online Arduino circuits. It also allows you to debug the code you used, check the wiring, and try out different circuit constructs. This is awesome too for beginners in the use of Arduino and experts in search of flexibility.

Frequently Asked Questions

Why does a circuit assembly fail?

Circuit assembly might fail due to certain reasons. Poor design, trace damage, physical damage, and component failure are reasons a circuit may fail.

Can I repair circuit cards?

Yes, you can repair circuit cards depending on the kind of damage. Before you can repair your circuit cards, you need to know the cause of the damage.


Circuit assembly involves several processes. The assembling of circuit cards is an important procedure in the PCB industry. In this article, we have reviewed important facts you need to know about circuit assembly.




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