You
are sure to find printed circuit boards in almost all electronic devices. That
ranges from radios, televisions, smartphones, LED lights, and computers.
In
any electronic equipment, a circuit board helps receive or send signals. But
how do circuit boards work? What are the roles of various PCB components like
transistors, diodes, resistors, and capacitors?
The
guide provides detailed information that helps answer questions like how PCBs
work and what a circuit board is.
What Is
a Circuit Board?
A
circuit board is a flat, non-conductive piece of material that holds different
electronic components joined by interconnective paths called traces. The
circuit board can be of single, double, or multilayers.
A Brief
History of Circuit Boards
Before
printed circuit boards (PCBs) were invented, early electronic devices used
point-to-point wiring. This method connected each electronic component with
wires by hand. It was complex, took up a lot of space, and often caused errors
like wrong connections, short circuits, or bad solder joints. Maintenance was
also difficult.
In
the 1930s, Austrian engineer Paul Eisler created the first modern circuit
board. He used a process to etch copper onto an insulating base. This replaced
manual wiring and made circuits easier to produce. His invention improved both
the reliability and efficiency of electronic products.
Over
the following decades, circuit board design kept improving. At first,
components were still soldered by hand. Later, engineers used software to
create PCB layouts, and machines were used for automated production. Today,
circuit boards support multilayer structures and high-density interconnect
(HDI) designs. These advances allow electronic devices to become smaller,
lighter, and smarter.
Types
of Circuit Boards
Single-Sided
(Single Layer)
A
single-layer PCB is also termed a single-sided circuit board. The type of
circuit board is easy to come across and attracts an affordable cost. Further,
a single-sided PCB has a conductive copper layer on one side, and the opposite
side features a layout for the electronics components.
Although
single-sided circuit boards are cheap to produce, they suffer some limitations.
Consequently, it isn't the preferred option for high-end applications.
Double-Sided
Double-sided
circuit boards are also termed as double-layer PCBs. Just like their
single-sided counterpart, double-sided features have a single substrate.
However, the core material features a thin layer of conductive material on
either side of the board.
Also,
double-sided circuit boards tap on the surface mount and through-hole
technologies. Doing so enables the circuits on either side to connect via the
plated through holes. What such a circuit board does is that it allows for the
mounting of components on both surfaces.
The
introduction of double-layer technology has enabled circuit boards to handle
more complex applications than before.
Multilayer
Unlike
single- or double-layer PCBs, multilayer circuit boards employ multiple
substrate materials. In other words, it's a circuit board that combines three
or more double-sided PCBs into one unit.
Thus,
in real life, you can find PCBs of four, six, eight, twelve, or even more
layers on the boards. In multiple-layer circuit boards, electronic components
are only on the top and bottom layers. All other stacked units help in
routing.
A
multiple-layer circuit board contains high component density and numerous
circuits in a smaller space. Therefore, multilayer circuit boards find
applications in computers, GPS, satellites, and aerospace systems.
Note
that multilayer circuit boards are demanding to design, expensive to
manufacture, and challenging to repair.
Flex
Circuits
Flex
circuits, as the name implies, are flexible and thus foldable. The flexible
PCBs can have single, dual, or multiple layers. The distinguishing feature is
their flexibility. Flexible printed circuit boards employ a supple substrate
material such as thin plastic, polyimide, or Kapton.
The
outstanding advantage of flexible printed circuit boards is their easy handling
and tolerance of extreme temperatures. Being flexible, the PCBs can assume the
shape of different electronic devices.
Rigid
Circuits
Unlike
a flex circuit, a rigid power board isn't flexible. The rigid printed circuit
board uses a non-flexible substrate material. So, once you design and
manufacture the board, you can not alter its shape.
Rigid
circuit boards excel in strength and durability. A computer's motherboard is a
typical example of a rigid PCB. Note that the power board can take any number
of layers.
Rigid-Flex
Rigid-flex
printed circuit boards are a blend of flexible and rigid boards. By blending
the two types of boards, rigid-flex PCBs are flexible yet still durable.
High-Frequency
The
high-frequency printed circuit boards find application in circuits requiring
fast data processing and high frequency. Sometimes, such circuits handle data
at speeds of up to two gigahertz. Such power boards are present in networking
devices, radios, microwaves, and mobile phones.
Aluminum
Backed PCBs
The
aluminum-backed PCBs use thick aluminum metal as the core material. However,
the aluminum substrate has a dielectric topping and thick conductive copper
layers.
Owing
to their design, aluminum-backed circuit boards are sturdy, give good heat
dissipation, and handle large currents. Some of their typical applications are
in LED lighting, the automotive industry, and power supplies.
Core
Function: How Do Circuit Boards Work?
The
main function of a circuit board (PCB) is to transmit and distribute electrical
signals between different electronic components. It creates electrical
connections through copper traces on the board surface, allowing each component
to operate as designed.
These
copper traces are usually created by an etching process and are placed on an
insulating substrate. They act like pathways, guiding electrical current from
the power source to the required components—such as chips, resistors,
capacitors, diodes, or connectors.
The
working process can be divided into the following steps:
•
Power Input: Electrical current first enters the electronic
board from an external power supply.
•
Signal Transmission: The current flows through copper
traces to different parts of the circuit board and to specific component
locations.
•
Function Execution: Each component performs its intended
task, such as controlling voltage, current, logic operations, or signal
processing.
•
Output: The processed signals are sent to the
output devices, such as a display, motor, or speaker.
Throughout
this process, the PCB ensures accurate and stable signal flow. This method of
signal routing is the foundation of proper operation in all electronic devices.
Key
Parts of a Circuit Board
To
understand how a circuit board works, it's important to first learn about its
physical structure. A standard printed circuit board (PCB) is made up of
multiple layers. Each layer has a specific function and plays a key role in
signal transmission and electrical performance.
Here
are the main structural layers of a circuit board:
•
Substrate: This is the base layer of the PCB.
It is usually made from FR4 fiberglass material. The substrate provides
mechanical support, structural strength, and electrical insulation for the
entire board.
•
Copper Layer: This is a conductive layer placed
directly on top of the substrate. It is usually made of copper. Through an
etching process, the copper is shaped into traces that connect different
circuit board components and carry electrical signals and power.
•
Solder Mask: This is a protective layer applied
over the copper traces. It is usually green. The solder mask prevents short
circuits during soldering and protects the copper from oxidation and physical
damage.
•
Silkscreen: Printed on top of the solder mask,
this layer includes text and symbols. It helps identify component locations,
reference numbers, and orientation, making assembly, testing, and repair
easier.
•
Vias and Pads: Vias are small holes that go
through the board and connect copper layers across different levels. Pads are
flat surfaces where component leads are soldered. They ensure secure and
reliable mounting of electronic components.
Each
of these layers plays an important role in how the PCB works. Choosing the
right materials and using a well-designed layer stack-up helps ensure stable
signal flow and improves the reliability of the entire electronic system.
Components
of a Circuit Board
You
can only understand how a PCB works after knowing its constituents. Each
mechanical and electrical device on a circuit board plays a distinct role. They
include the following:
Transistors
A
transistor is a semiconductor device that plays a vital part in a circuit
board. It helps to amplify electronic signals or plays the role of a
signal-controlled switch.
The
amplified signal then travels through the trace and switches on another
high-power semiconductor device. Transistors on a circuit board are either PNP
or NPN type.
Resistors
Another
vital component of a circuit board is a resistor. Resistors play the role of
regulating the amount of current flowing through a device.
When
current flows through a resistor, the device dissipates heat and thus regulates
the current. They are of two types: fixed and variable. On a printed circuit
board, resistors have the symbol of the letter R.
Capacitors
The
symbol for a capacitor is the letter C. Capacitors store charges in an
electrostatic field for a momentary period. It then releases an outburst of
power at the appropriate time through discharge. One widespread use of
capacitors is smoothening the ripples of a rectified AC power.
Diodes
Diodes
are semiconductor devices that conduct current in one direction only. They
differ in size and amount of current they can safely carry without breaking
down.
The
unidirectional property of the diode makes it ideal for rectifying alternating
current, AC into direct current, DC. One famous type of diode is the
light-emitting diode, LED. As the name suggests, LED glows when an electric
current passes through it.
Inductors
An
inductor is yet another common component of a circuit board. An inductor stores
energy from an electric current in a magnetic field. In most cases, inductors
are used together with capacitors to form an LC circuit.
Transformers
Transformers
have electromagnetic properties. The role of a transformer is to moderate the
energy transfer from one part of the board to the next. While doing so, it
isolates one part of the circuit board and protects sensitive devices. A
transformer can either step up or down power in a circuit as required.
Switch
A
switch in the on position allows current to flow. However, when the switch is
open, it cuts off the current through a board.
Integrated
Circuit (IC)
An
integrated circuit is commonly known as an IC. As the name implies, an IC
contains numerous circuits involving miniaturized components integrated into
it. Another name for ICs is microchips, and they play multiple roles in a
circuit board.
How Are
Circuit Boards Made?
Printed
circuit board (PCB) manufacturing is a precise and complex process. Its goal is
to turn a digital PCB layout designed by engineers into a real, working
electronic board. The process includes several key steps. Each step affects the
final performance and reliability of the product.
Below
are the main steps of PCB manufacturing, explained in order:
1.
Design and Layout
Engineers
use CAD (Computer-Aided Design) software to create the circuit board design.
This includes drawing the circuit schematic, placing components, planning
traces, and defining layer structure. The final output is the Gerber files,
which are used in manufacturing.
2.
Image Transfer
The
PCB design is printed onto a copper-clad laminate (the base material). This is
done using exposure and development processes. This step defines the basic
shape and location of the copper traces.
3.
Etching
Unwanted
copper is removed from the board. Only the necessary conductive traces remain.
These traces form the actual electrical paths between components. This step
ensures the PCB layout is accurately formed.
4.
Drilling and Plating
CNC
machines drill holes into the PCB for component leads and vias. Then, the holes
are plated with copper. This allows electrical connections between different
copper layers.
5.
Solder Mask and Silkscreen
A
solder mask layer is applied to cover the traces. It is usually green and
protects the copper from oxidation and short circuits. After that, a silkscreen
layer is added to show part numbers, component positions, and orientation. This
helps with assembly and inspection.
6.
Component Assembly (PCBA)
Electronic
components are mounted on the board according to the design. This can use SMT
(Surface Mount Technology) or THT (Through-Hole Technology), depending on the
component type and product requirements.
7.
Testing and Inspection
The
assembled board is tested with electrical, functional, and visual inspections.
This checks for open circuits, short circuits, soldering problems, and if all
key components work properly. These steps ensure that the PCB works correctly
and meets quality standards.
Common
Questions About How Circuit Boards Work (FAQs)
Q1:
How do circuit boards work in simple terms?
They
use copper pathways to carry electrical signals between components, enabling
devices to perform tasks.
Q2:
What are the main parts of a circuit board?
Substrate,
a copper layer, solder mask, silkscreen, and various circuit board components
like resistors, ICs, and capacitors.
Q3:
How does a circuit board get designed?
Using
CAD tools, engineers create a PCB layout based on function, component
placement, and routing needs.
Q4:
How do PCBs work in harsh environments?
By
using durable materials, conformal coatings, and proper circuit board design,
PCBs can withstand heat, vibration, and moisture.
Q5:
What’s the difference between a PCB and an electronic board?
They’re
essentially the same—“electronic board” is a general term, while “PCB”
specifically refers to the physical platform.
Q6:
Do circuit boards use AC or DC?
Most
circuit boards, if not all, use DC (direct current) instead of AC (alternating
current). In most cases, a battery or rectified AC provides the direct current
the board requires. A rectifier unit that changes AC to DC consists of a
transformer, rectifier diodes, and a filter circuit.
Q7:
What powers a circuit board?
A
circuit board receives its power from a battery or PCB power supply. A PCB
power supply takes power from the wall socket and changes it to a DC level that
the board needs.
Q8:
What is inside a circuit board?
A
single-sided circuit board has a single layer of conductive copper material on
one side and another side for mounting electronic components on the same board.
Q9:
Why are circuit boards usually green?
Most
circuit boards are usually green since they use the green protective solder
mask. So the entire board isn't green through, only the outer part. The mask
protects the traces from moisture and dust and prevents solder messes.
In
the olden times, circuit board inspection was mainly by eye inspection. And
green color reduces eye fatigue.
Conclusion
Modern
electronic devices have circuit boards of varying sizes. But the principle of
what a circuit board does is the same. Whether it's a single, dual, or
multilayer board, it relies on various electronic components to accomplish its
function.
