PCBs Explained: A Simple Guide to Printed Circuit Boards

Printed Circuit Boards (PCBs) are the essential building blocks behind almost all modern electronic devices. PCBs play an important role in that they provide electrical interconnections between electronic components, rigid support to hold components, and a compact package that can be integrated into an end product. They are the main component in an electronic device that is responsible for form and function, and they allow advanced semiconductors to communicate with each other at very high data rates.

From smartphones and computers to home appliances and industrial equipment, PCBs are what allow these devices to perform their various functions reliably. In this simple guide, we’ll explain what PCBs are, how they work, and why they're so crucial in today's technology-driven world.

What is a PCB?

A Printed Circuit Board (PCB) is a flat, thin board made from insulating materials, such as fiberglass, with conductive pathways etched onto it. These pathways, also called traces, allow electrical current to flow between different components on the board, connecting everything into a functional circuit. Components like resistors, capacitors, transistors, and integrated circuits (ICs) are mounted onto the board and connected through these pathways. PCBs also provide mechanical support for electronic components so that a device can be mounted in an enclosure.

PCBs can be single-sided (with only one layer of conductive material), double-sided, or multilayered, depending on the complexity of the design and the number of connections required. During manufacturing, the inner copper layers are etched, leaving the intended traces of copper for connecting components in the circuit board. Multiple etched layers are laminated in succession until the printed circuit board stack-up is complete. This is the overall process used in PCB fabrication.

Components of a PCB:

A PCB's layer count is commonly based on its number of conductive layers. However, a PCB also includes other types of layers, which are laminated together in alternating patterns of conductive and insulating material. Today's PCBs always contain the following four types of layers:

• Substrate: This is the base material of the PCB, typically made of fiberglass (FR4) or metal, providing rigidity and insulation.

• Copper Layer: On top of the substrate, a thin layer of copper is applied, which creates the conductive pathways. There may be one or multiple copper layers, depending on the complexity of the PCB.

• Solder Mask: The green (or other colored) protective layer that covers the copper traces to prevent short circuits and damage during handling.

• Silkscreen: White markings printed on the PCB that provide labels and symbols to help identify components and connections.

A PCB is made up of a mix of these four types of layers. A single-sided PCB includes one substrate layer, one copper layer, a solder mask, and a silkscreen. A double-sided PCB includes one substrate, two copper layers, solder masks on both sides, and usually a silkscreen.Multilayer PCB might also use prepreg as a layer. Prepreg is a dielectric material that's sandwiched between two core layers or between core and conductor layers.

A Dive into PCB History:

In the past, electronics were designed and assembled from small integrated circuits (ICs) and discrete components, which were connected together using wires, and the components were mounted to a rigid substrate. This original substrate was initially a material called bakelite, which was used to replace the top ply on a sheet of plywood. The number of wires was so great that they could get tangled or occupy a large space within a design. Debugging was difficult and reliability suffered. Manufacturing was also slow, where multiple components and their wired connections were manually soldered.

Today, standard designs can have many small components, such as tiny ICs, very small passive components, and advanced chips with very high pin counts. It's impossible to manually connect all of these components together with soldered wires, so the copper connections are deposited directly on insulating substrates as described in the above manufacturing process. Many of today's devices are advanced high density interconnect (HDI) designs with thousands of connections and multiple electrical interfaces, powering everything from smartphones to heart rate monitors to rockets.

Types of PCBs

There are different types of PCBs designed to meet various needs based on complexity and application:

1. Single-Sided PCB: These have only one layer of copper for the conductive traces. They are simple, inexpensive, and commonly used in low-cost electronics.

Ideal for basic devices like calculators, radios, LED lights, and power supplies. Advantages: lowest cost and easiest to manufacture. Disadvantages: limited circuit complexity and component density due to traces on only one side.

2. Double-Sided PCB: These PCBs have copper layers on both sides of the board, allowing more complex circuits. They are used in consumer electronics and more intricate devices.

Common in products like amplifiers, vending machines, and automotive dashboards. Advantages: higher component density and better routing flexibility than single-sided. Disadvantages: slightly higher cost and requires plated through-holes for interlayer connections.

3. Rigid PCB: As the name suggests, these PCBs are rigid and cannot be bent or flexed. They are widely used in durable electronics.

Found in nearly all standard devices like desktop computers, televisions, and industrial controls. Advantages: strong mechanical support and cost-effective for flat designs. Disadvantages: inflexible, not suitable for compact or moving parts.

4. Flexible PCB: These are made from flexible materials, allowing them to bend and twist. They are typically used in wearables, cameras, and compact devices.

Common in smartwatches, medical wearables, foldable phones, and printer heads. Advantages: space-saving, lightweight, and able to fit into irregular shapes. Disadvantages: higher cost and more challenging to assemble.

5. Rigid-Flex PCB: A combination of rigid and flexible PCBs, used in applications that require flexibility in some parts while maintaining stability in others.

Widely applied in aerospace, military equipment, high-end medical devices, and foldable electronics. Advantages: combines durability with dynamic flexibility, reducing connectors and improving reliability. Disadvantages: most expensive and complex to design and manufacture.

6. Multilayer PCB: Consists of multiple layers of copper traces, stacked and insulated from each other. These PCBs are used in high-performance devices like smartphones, computers, and medical equipment.

In multilayer PCBs, signals need to travel between the different copper layers. This is achieved through vias—small plated holes that act as vertical conductive pathways. The most common type is the through-hole via, which runs through the entire board. More advanced designs may use blind vias (connecting an outer layer to an inner layer) or buried vias (connecting only inner layers), allowing even denser and more compact circuits.

How is a PCB made?

The question “What is a PCB?”also concerns its appearance, its composition, and how it is made. At first glance, a printed circuit board appears to use a fairly simple technique to arrange, mount, and connect components.However, it's a fairly complex process involving numerous technical stages and cutting-edge manufacturing systems.

A PCB is a circuit board made from multiple layers of materials, arranged somewhat like a sandwich. The number of layers can be increased for more complex circuit boards. A typical simple PCB consists of the four layers mentioned above. The early stages of PCB design involve drawing out the circuit you want the board to support, and testing it for basic function. The circuit design is then transferred to a manufacturer for further fabrication. The steps include:

• Design and Layout
• Printing the PCB Design
• Etching
• Drilling
• Plating
• Solder Mask Application
• Silkscreen Printing
• Finishing
• Inspection and Testing

All these steps are discussed in very detail, see our ultimate guide on PCB manufacturing. Which covers all the design and fabrication aspects of a printed circuit board.

How Does a PCB Work?

PCBs provide the foundation for electronic devices, enabling components to communicate with each other through well-organized conductive traces. Here’s a basic breakdown of how a PCB works:

Power Distribution: The PCB routes power from the battery or power supply to all the necessary components.

Signal Flow: Traces on the PCB carry signals (electrical currents) between different components, allowing them to communicate and perform tasks.

Component Support: PCBs provide a sturdy structure where components can be mounted securely, keeping everything in place and maintaining connections.

The careful arrangement of traces ensures signals are transmitted accurately and efficiently, while the board’s design minimizes the risk of interference or malfunction.

Why Are PCBs Important?

PCBs are vital to the functioning of modern electronics for several reasons:

Compact Design: PCBs allow complex circuits to be compact and neatly organized, enabling smaller devices without compromising performance.

Reliability: PCBs ensure stable connections and minimal electrical interference, contributing to the reliable functioning of electronic devices.

Cost-Effective Production: PCBs can be mass-produced, making them cost-effective for manufacturers and consumers alike.

Durability: With protective layers and robust materials, PCBs can withstand physical and environmental stresses, ensuring long-lasting performance.

Applications of PCBs

Printed Circuit Boards (PCBs) are integral to nearly every modern electronic device. In consumer electronics, they power smartphones, laptops, televisions, and gaming consoles. The automotive industry depends on PCBs for critical systems such as navigation, entertainment, and engine control.

In the medical field, PCBs are crucial for devices like heart monitors and imaging equipment, ensuring accurate diagnostics and patient care. Industrial machinery, from automation systems to control panels, also relies on PCBs for efficient operation. Additionally, the aerospace sector uses advanced PCBs in spacecraft and aviation equipment, designed to endure extreme conditions and meet high-performance demands.

Conclusion

Printed Circuit Boards are the foundation of modern electronics, enabling the functionality, compactness, and reliability we've come to expect from our devices. From simple gadgets to highly advanced systems, PCBs make the interconnected world we live in possible. As technology evolves, the role of PCBs will continue to expand, driving innovation across industries and enhancing the devices that shape our daily lives.

FAQ: Printed Circuit Boards (PCBs)

1.What does PCB stand for, and what is its main purpose?

PCB stands for Printed Circuit Board. It is a board that provides electrical connections between electronic components through conductive copper traces, while also offering mechanical support.

2.What are the most common types of PCBs?

Common types include single-sided (copper on one side), double-sided (copper on both sides), multilayer (multiple copper layers), rigid, flexible, and rigid-flex (combining rigid and flexible sections).

3.What are the four basic layers of a typical PCB?

A typical PCB consists of:  Substrate (usually FR-4 fiberglass for rigidity and insulation)  

Copper layer (for conductive traces)  

Solder mask (protective coating, usually green)  

Silkscreen (labels and markings)

4.How do multilayer PCBs connect signals between layers?

Multilayer PCBs use vias—small plated holes that act as vertical conductive pathways. The most common are through-hole vias that run through the entire board; advanced designs may include blind or buried vias for denser layouts.

5.Why are most PCBs green?

The green color comes from the solder mask layer, which protects the copper traces and prevents shorts. Green is the traditional and most widely used color for good contrast with white silkscreen and copper, though other colors are available.