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In the realm of electronics, Printed Circuit Boards (PCBs) are the backbone of nearly all electronic devices, from smartphones and computers to medical equipment and automotive systems. But what exactly is on a PCB, and how does it all come together to create functional electronic circuits? In this blog, we’ll explore the components and structure of a PCB, as well as the various elements that make up a modern circuit board.
A Printed Circuit Board (PCB) is a flat board made of non-conductive material (typically fiberglass or plastic) that holds and connects various electronic components. The board is designed with conductive pathways—called traces—that connect different parts of the circuit, enabling the flow of electrical signals and power between components. These traces are usually made of copper and are etched or printed onto the surface of the board.
PCBs come in various forms, from simple single-layer boards to complex multi-layer designs that allow for more compact and advanced circuitry. The specific components and the design of the PCB depend on the type of application and the complexity of the device.
Let's start with a PCB based on FPGA extension training without soldered components. The main elements that make up a PCB can be seen in the diagram.
Component refers to a component that is soldered to a PCB.
PCB carries various components. There are many different types of components and their packaging on the PCB varies greatly.
Even the same type of component is available in many different packages. For example, a 14-pin op-amp LM324 is available in DIP14, SO-14, SSOP14, and so on.
Devices can be simply categorized into two broad groups based on package type.
Holes need to be punched in the circuit board to hold the pins in place. The pins of the component span the Top layer or Front layer and Bottom layer or Back layer.
Components appear on only one layer, either on the top layer or on the bottom layer. But a device is only on one of the layers.
As the system of the product runs faster and faster, the integration of the device is getting higher and higher.
Surface mount devices (SMDs) became mainstream.
Because it is small, cheap, and has good high-frequency characteristics. And circuit boards are easier to process and produce, and the density of the boards can be higher.
Additionally, you should be careful to distinguish between two English terms related to surface mount devices:
(1) SMT, is the abbreviation for Surface Mount Technology.
(2) SMD, is the abbreviation of Surface Mount Device.
The pin of the device is secured to the board by a pad and is electrically connected to other pads. The pads are an important part of the device package.
Depending on the type of packaging of the device. It has through hole pads that run through the top and bottom layers.
As well as surface mount pads that are only on the top or bottom layer.
Some devices have both pads and they come in a variety of shapes and sizes.
When building component packages with a CAD tool, set them up correctly according to the definitions in the datasheet for that device.
When using the package that comes with the tool or downloading a package from the Internet, be sure to double-check it. Make sure that the size of the pads meets the specifications in the device manual.
The silkscreen layer is a printed layer that is applied to the surface of the PCB to indicate important information such as component labels, reference designators, and logos. This layer is usually printed in white ink and is essential for assembly and troubleshooting. It helps technicians and engineers identify components, pin 1 orientations, and other critical features during the manufacturing and repair processes.
Components are generally in the Top layer or Bottom layer of the PCB. In addition to the "physical" layers that connect the signals, there are also layers that are used for processing, installation, and information indication. We generally refer to single-panel, double-panel, 4-layer boards, etc. as layers with electrical connections (signals, power, ground, etc.). However, the layers in CAD tools are much broader.
When designing PCBs with CAD tools, it is important to clearly understand the meaning and role of these layers. And to set up and use them correctly.
The layers of the circuit board is almost invisible to the naked eye. If you want to learn, please refer to "How to identify the number of layers of a circuit board with the naked eye" (just click the link).
Track is the copper wire used on the PCB to make electrical connections between devices and devices. The Wire on the schematic is the ideal connection.
Because there is no impedance, current limitation, and interference with each other.
However, the actual wires on the board have a certain impedance (depending on the length and width of the wires, the board, the vias, etc.).
There are also practical problems such as mutual electromagnetic interference between the wires.
After all, space on the board is limited.
The length and width of the wires, as well as the distance between wires, are set according to the physical space of the board and the number of signals to be connected.
Depending on the nature of the signal and the constraints of the alignment space on the board, the width varies.
For example:
(1) Alignments carrying large currents should be as short and thick as possible.
(2) Differential lines carrying signals in pairs should be as equal in length as possible.
(3) The transmission impedance of high-speed digital signal lines should match the output impedance of the transmitting device and the input impedance of the receiving device as much as possible.
PCB board alignment
Vias are small holes drilled into the PCB that allow signals and power to pass between different layers of the board. Vias are used in multi-layer PCBs to connect different layers of circuitry, allowing for more compact and complex designs. The Via can be compared to an underground tunnel in life.
Depending on the setup of the connecting signal layer, there are three main types of vias:
(1) Through hole. Connected to the upper and lower levels, It is visible above and below.
(2) Buried via. Inside the board, connecting two layers inside the board that are not visible on the surface.
(3) Blind via. Only one side is visible, the other is not. Blind hole connects a signal from a surface layer to one of the internal signal layers.
The shape and size of the vias are not set randomly. This depends on the characteristics of the connected signals and the process requirements of the PCB processor.
The Silk Screen is used to mark the outline, orientation, numbering, and remarks of components on the PCB. This is for easy identification.
The name of the silk screen varies from one CAD software to another.
For example, the top layer of the silkscreen in Altium Designer is called Top overlay,. And the bottom layer is called Bottom overlay.
Screen Printing on PCB
The solder mask is a protective layer applied over the copper traces to prevent solder from flowing onto areas where it is not wanted. This layer is typically green (though other colors are also common) and helps improve the electrical reliability of the PCB by preventing short circuits, corrosion, and oxidation of the copper.
The solder mask also provides a non-conductive barrier around the copper traces, protecting them from external damage and preventing accidental solder bridges during assembly.
Different colors of boards are actually different solder-mask colors selected. Different colors of solder resist are used to get different colors of boards.
When the same board is processed, different colors of solder resist are selected. And different colors of boards are obtained.
Many companies or teams purposely use a certain color for a certain series of boards to show off their style. For example, Spark Fun's boards are basically all red.
Even the sides of the same board may use different colors of solder-mask. For example, the Arduino Uno board has a green color on the front and part of the back is white.
When choosing a different solder-mask color when processing a fast board, the price and delivery time may vary. In general, green is the most versatile and fastest.
On many boards there are usually some round holes with an inner diameter of 2.5~3mm near the perimeter. They are called Mounting Hole.
Some of these holes are used to connect the circuit boards that hold the physical laminate in place.
For prototypes under development, holes are punched in the four corners even if no other boards need to be connected.
This is to facilitate debugging. Without interfering with other electrical connections, the four holes can be connected to "ground" on the board.
A more reliable way is to connect an oscilloscope probe and a grounding clamp to the "ground" on the board during debugging.
This eliminates the need to solder a "ground" test point. Of course, the "ground point" of the high-speed circuit must be close to the signal under test.
PCBs come in various configurations depending on the complexity of the circuit. The most common types are:
Single-layer PCBs: Have one conductive layer (usually copper) and are used for simple, low-density applications.
Double-sided PCBs: Have conductive layers on both sides of the board, allowing for more complex circuits and component placement.
Multi-layer PCBs: Contain multiple layers of conductive material, typically separated by insulating layers. These boards allow for complex circuitry in a compact form factor, making them ideal for high-performance devices like smartphones and computers.
A PCB is a sophisticated assembly of conductive traces, components, and layers designed to connect and support the electrical components of an electronic device. Understanding what is on a PCB—ranging from copper traces and pads to the various electronic components—helps engineers and designers create efficient, reliable, and functional circuits. Whether it's a simple single-layer design or a highly complex multi-layer board, the components and structure of the PCB are carefully selected to meet the specific requirements of the device it powers. As technology advances, the complexity of PCBs continues to grow, supporting the ever-evolving demands of modern electronics.
