Introduction to Printed Circuit Boards(PCB)

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All over the world, we are surrounded by electronic devices. Whether we are working in offices or at homes, it is very easy to come across an electronic device. Some of them we walk with such smartphones, tablets, and laptops. Some are amazingly beautiful while others are subtle. All these devices have a board inside them that is referred to as a printed circuit board (PCB).

The printed circuit boards have been available since 1945 when they were discovered for military use during World War 2. When they were made commercially available, many manufacturers adopted them as the most suitable method for assembling electronics as compared to the traditional available point-to-point connection of the electronic circuits.

Over the years, the area of the printed circuit board has seen immense growth and also witnessed the introduction of new technologies in circuitry generation to meet the market demand and also to accommodate the new trends in the area of electronics. The knowledge about the electronic design and printed circuit boards can fill a shelve and today we are going to have a look at the basic introduction of it.

Definition of Printed Circuit Board.

A printed circuit board is an electronic rigid structure that is made of embedded metal wires referred to as traces/tracks and some large areas of metals referred to as planes. The electronic components are then fixed on the top, bottom, or even on both sides of the board using the metal pads. They can also be fixed on the sides of the board. The metal parts are also fixed on the boards to allow the components to be interconnected together. The board can be made up of a single layer of circuitry with components connected on either side or both or even can be made up of multiple layers of the circuitry that are stacked together.

• The board plane is made up of a dielectric material that is free from electrical conductivity so that it can be free from contaminating the electrical signals.
• The FR-4 is the standard material that is used in the production of the PCBs while the metal planes and the traces are made up of copper material.
• The printed circuit boards find great applications in many fields of electronics. You can find complex boards on computers and telecommunications and simple boards in child toys.
• Some boards are made up of specialized materials due to the high frictions and frequencies that they operate with such as high temperatures while others are made up of flexible materials so that they can be bent or even fitted in their areas of use. Also, some of the boards have heavy copper traces dues to their applications. In the current market, you will come across boards that have been built for extreme environments such as sensors that operate under high temperatures for example in car engines and boilers.

Although these are some of the noticed applications of the printed circuit boards, they all follow a similar construction process. Let us have a look at it below:

 

The PCB Making Process.

To come up with a physical printed circuit board, you must start by designing it. The design process starts with Electronic Design Automation which is made successful by the use of the design tool.

• The design process is divided into two stages

1. The schematic which involves the creation of the circuit connectivity in a diagram
2. The PCB layout involves the creation of the physical circuit board.

• Step number one involves the creation of the libraries that you need to use in your design. These libraries comprise the symbols, the footprints, and the 3D model of the components that you want to use.
• Once all the models are ready, the next things involve the creation of the schematic logical diagram. The CAD tools are used to place the symbols in the working space and interconnect them to form circuitry.

 

• At the same time, we have to simulate the circuit to ensure that it is functioning as it is intended. Once this is done, the simulated circuitry connection is passed to the next stage which is the PCB layout stage.
• At the layout stage, the schematic is received as nets that connect two or more components. With the outline of the PCB desired shape, the designer will place every component on their desired space.

 

• Once the components have been laid optimally, the next step is to connect the pins using the traces. The design tool will have several in-build rules and restrictions that stop the traces from crossing and touching each net and also control the size of the width governing each trace. Once the routing is completed, we shall have to use the design tool to generate all the documents required for the manufacturing process to be accomplished.

 

It is very clear that the design and manufacturing of the printed circuit board is a step-by-step process that starts with the design and simulation of the schematic, then the layout process where routing of the board is done, and also the generation of the relevant manufacturing files before delivering the final design to the manufacturer. The relevant manufacturing files that should be generated from the design tool include the pick and place files, the bill of material files, the GERBER files, and the drill files. The final step in the building of the PCB will involve assembling the BOM and building the final board. Let us have an in deep looking into these steps.

Important Files in the PCB Design and Manufacturing Process

During the process of the design of the PCB, before proceeding to order the PCB through the manufacturers’ site, there are different types of files that you need to generate using the Design Tool. Let us discuss them below:

GERBER files

They are the most common and also the most used files in the area of electronic design. They can be produced by almost all the EDA tools. In manufacturing, they are referred to as stencil data or light painting files.

The GERBER file is in two different types: RS274-X and RS274-D.

The GERBER file is a very crucial requirement in the design process, and if the file has inconsistent then the design will not be that good.

BOM files

BOM also known as a bill of the material file shows the list of components that are needed to make the PCB and does the matching of the components to the correct designator in the PCB layout. It also has a column for the source of the part, part number, and the manufacturer of the part. The file is in excel form as shown below.

Pick and Place Files

This is simply the list of all the components in the design and their respective coordinates and the rotation. Most EDA tools can generate the components’ x-y coordinates and how they have been rotated. They are always in excel form as shown below.

 

Types of Printed Circuit Boards

The printed circuit boards are classified into many different types depending of the number of layers that are available in the board and also the manufacturing process that was used. They are classified as follows:

Single-Sided PCBs

This is the most common PCB with a single copper layer above its substrate.

• The electrical components are placed on one side of this board. The conducting paths cannot intersect since it utilizes a single layer hence a lot of space is needed.

Double-Sided PCBs

A thin layer of conducting copper layer is added on both sides of the boards and holes drilled through the board allow the metal parts to be connected across both layers.

• These types connect the parts from one side to the other using one or two methods; ie THT or SMT.

Multilayer PCBs

This has more than two copper layers. Generally, a board featuring at least three layers will fall under this category.

What You Need to Know before Doing a PCB Design.

Many of us would like to become PCB designers. To some, it might be seen as an easy journey, and to others, it might become a complex journey. Here am going to take you through what you need to know before becoming an expert. First, you need to know the many electronic components involved in the design process. Secondly, you should have the know-how of the necessary EDA tools such as KiCAD, Proteus, EasyCAD, and many others which will help you in doing the design before sending the complete design to the manufacturer. Thirdly, we shall have a look at the different, materials that are very necessary for building the board used for the circuitry attachment and finally we shall see the manufacturing process is done especially the mass production. Let us start with the component.

PCB Design Components/ Elements.

PCB design starts with an Electric Circuit. An electric circuit is an interconnection between components of various types and purposes in which there is at least one enclosed path in which an electric current can flow as shown in the image below.

performance of a system be it mechanical or electrical is done by drawing of its electrical circuit equivalent. by simulating this circuit, any system can be studied. This tells us that the performance of any system can be studied by mastering its circuit theory.

Below are the elements that are commonly used in electronic circuits;

Active elements:

are elements of the circuit that have their energy. They are independent of an external power source. They are of two types that is a current source and a voltage source.

Passive elements:

these elements do not possess energy of their own. They depend on an external source of energy. This is the area of focus of this article and therefore more discussion will follow. An example of this is a resistor.

Linear and non-linear Elements:

• Linear elements show the linear characteristic of the voltage and current which is in most cases a straight line. Example a resistor.
• For the non-linear elements, the v-I do not follow a straight line. Example diode

Bilateral and unilateral elements:

Bilateral elements have the same relation existing between voltage and current for current flowing in bi- directions. Example current source.

Unilateral elements do not have the same relationship existing between their voltage and current flow. Example a silicon diode.

Lumped and distributed elements:

Talking about the lumped element, our focus shifts to those very tiny in size elements in which actions take place simultaneously. We can have a few examples such as resistors, inductors, and capacitors.

On distributed elements, we can define them as those elements that are not separatable electrically for analysis. They include for example a transmission line that has distributed parameters along its length and may extend for hundreds of miles.

Now after having a reminder on what electrical elements are, let us go back to the purpose of this article. Our focus is on passive elements and we have already introduced what they are in our introduction.

Passive Electronic Components.

Passive elements are those elements that do not possess energy of their own. They are dependent on an external source of energy such as a current source or a voltage source. These elements do not generate power but they dissipate energy.

Passive elements are part of electronic circuits. 99% of the circuits we have around have either one or more passive elements. Before we get deeper, I would also like you to know that we have different techniques of how to fix components on a PCB board. Yes, two methods;

• Through-hole technique; the PCB board has holes drilled through them where the components with long legs are fitted through and soldered. It was the first method to be used although today it is not in much use.
• Surface mounting techniques; in this technique, the components or elements are laid on the surface of a PCB board then it is interconnected through copper pores. This is the latest technology that has led to the generation of compact and small components hence leading to reduced board sizes.

Having this in mind, it is very important to note that, passive elements also exist as a through-hole device (THD) or as a surface-mount device (SMD).

 

Let us now shift our focus to some passive elements that are commonly in use and are used. This will give us an early signal on things to consider while using passive elements. You cannot use an element without knowing what it is, what it does, and where to use it.

The Material used in the PCB Manufacturing

There are three types of PCBs and all will have different types of material. However, they all have similar primary materials. below, we are going to have a discussion on the different materials used in the manufacturing of the printed circuit boards.

Substrates

This forms the base of any printed circuit board upon which the manufacturer will mount the components and create the circuit to make the board complete.

• The type of the board is depended on the type of material that forms the base.
• Mainly there is the availability of two materials that are commonly used by the manufacturer to form the base of any given PCB namely; the fiberglass substrate and the plastic substrate.
• The fiberglass substrate is best suited for rigid, strong, and flexible PCBs used in the area of medicine.
• The plastic substrate is the cheapest option and also the most flexible option. Therefore, most manufacturers go for the plastic substrate. Plastic substrate durability is dependent on which type of material is used which includes; liquid crystal, polyimide, and polyester.

Conducting Material

Besides the nonconducting substrate, in any given printed circuit board is the conducting material that facilitates the creation of the traces and the completing of the circuit. This is made up of copper material.

• How the copper sheet is laid is defined by the designer depending on the usability of the board.

Solder Mask

This is a protective layer that is used to insulate the copper traces and protects them from damages such as short circuits and environmental dust and moisture.

• Without the soldering mask, oxidation will take place on the solder liquid hence making the circuit stop working.
• Besides the protection function, the solder mask determines the color of the printed circuit board.
• The most common color is green, but manufacturers have come up with solder masks of different colors such as blue, red, etc.

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