Printed Circuit Board

Whether it be a television remote or a satellite orbiting around the earth, every electronic device’s brain is assembled on a Printed Circuit Board (PCB).

Electronic devices get their functionality from the components assembled on printed circuit boards, so printed circuit boards are an essential element in every electronic device.

But why do some PCBs break upon stress, whereas some PCBs can even fold?

There are several types of PCBs, and each type has unique characteristics.

For example, rigid PCBs are robust, heavy, and economical for bulk production, whereas flexible PCBs are flexible and easily bendable.

They are robust, lightweight, and economical in the case of 3D circuits. Similarly, the other types of PCBs also have unique features that make them suitable for certain applications.

Choosing the right kind of PCB extensively affects the performance and life of a circuit.

Before proceeding to choose a printed circuit board type, let’s take a look at how the various types of printed circuit boards differ?

Printed Circuit Board Types

There are several types of printed circuit boards, and all types are made of unique materials.

Most manufacturers classify single-layer, double-layer, and multi-layer PCBs under the types of PCBs.

But it is essential to understand that the single-layer, double-layer, and multi-layer corresponds to only the number of layers; they exist in almost all types of boards.

For example, there are single-layer, double-layer, and multi-layer flexible boards.

However, for ease of understanding, the single-layer, double-layer, and multi-layer categories are often classified as independent types.

Similarly, the high-frequency printed circuit boards can be any type of PCB, like rigid or flexible; the only difference comes in PCB development processes and design.

Now let’s take a look at all types of PCBs in detail.

Single-layer Printed Circuit Boards

Single-layer PCBs are also known as single-sided PCBs. They are the most common kind of PCBs used.

As the name suggests, only one side of the single-layer printed circuit board is designed to hold the circuit.

Single-layer PCBs are made of a substrate layer, which forms the board foundation, and the second layer is a conductive layer, typically made of copper.

The circuit traces are crafted out of the copper layer, and the circuit is soldered on the copper layer.

These two layers are the building blocks of a single-layer printed circuit board; however, more layers are applied to the PCB.

Once the PCB design trace is applied on the board, a silkscreen layer is applied for marking the component values, manufacturer’s comments, and essential details.

The silkscreen has no role in PCB functionality, but it keeps the developer well informed of the design.

Then comes a solder mask layer, which is applied to the board after the components are soldered.

This layer’s only function is to protect the solder against oxidation (corrosion) and potential pollutants that can affect the circuit.

Since the single-layer PCBs are simple, easy to manufacture, and economical in bulk productions, they are commonly used in simple electronic products.

They are mostly used for assembling through-hole components, but they are also used for surface mount devices.

The manufacturing cost difference is significant compared to the other types of boards; single-layer PCBs are comparatively economical.

But these PCBs have some limitations too.

Single-layer Printed circuit boards are not feasible in all cases; they cannot hold huge circuits in compact space like double-layer or multi-layer PCBs.

Double-layer Printed Circuit Boards

Double-layer PCBs can carry circuits on both sides, which makes them more useful in complex circuits.

The primary difference in the construction of single-layer and double-layer PCBs is the number of layers on board.

There is only one substrate layer but two conductive layers, the electronic components can be assembled on both sides.

It enables the development of complex circuits on a smaller piece of a printed circuit board.

Moreover, the connection between both sides of the PCB connects components on both sides without any jumps.

Since double-layer printed circuit boards can hold large circuits, they are also commonly used.

Alike single-layer PCBs, double-layer PCBs also support both through-hole and surface mount device assembling.

Since double-layer PCBs offer twice the space of a single-layer printed circuit board of the same size, the overall weight is lighter than single-layer PCBs.

This is because two single-layer PCBs carry two layers of substrate and two copper layers, whereas a double-layer PCB has two layers of copper but only one layer of a substrate.

Apart from that, the double-layer PCB manufacturing process also takes less time.

The only disadvantage of double-layer printed circuit boards is that they are complicated to handle.

Multilayer Printed Circuit Boards

Multilayer Printed Circuit Board

As the name says, multi-layer PCBs are made up of multiple layers.

Like double-layer PCBs, they have more than one copper layer but more than one substrate layer too.

Multi-layer PCBs usually have 3-14 layers depending upon the circuit design. The layers are interconnected just like in double-layer printed circuit boards.

Alike single-layer and multi-layer PCBs, the solder mask and silkscreen layers are applied on multi-layer printed circuit boards.

Multi-layer printed circuit boards are most commonly used for assembling huge circuits that require lots of space or requires multiple circuit jumps.

Since multi-layer PCBs provide much more space for circuits than single-layer and double-layer PCBs, they are most useful for developing complex circuits.

But with its ability to hold huge circuits comes a disadvantage; multi-layer printed circuit board manufacturing is quite complicated. A small mistake in a single layer can ruin the whole board.

Rigid Printed Circuit Boards

Rigid printed circuit boards are the most commonly used type in electronics.

They are hard and do not bend easily, which is why they are named rigid PCBs.

As already explained, single, double and multi are just the number of layers, and they can exist in all types of PCBs; the rigid printed circuit boards can be single-layer, double-layer, or multi-layer.

The single-layer rigid printed circuit boards are widely used in small-scale electronic devices whose circuits are simple and do not require much space.

The rigid nature of these printed circuit boards comes from their substrate.

Fiber-glass and resin-based substrates are widely used for developing rigid PCBs.

Their rigid property gives them excellent strength to hold heavy components.

Moreover, rigid printed circuit boards are more suitable for assembling through-hole components than flexible printed circuit boards.

However, rigid circuit boards have their limitations; their rigid behavior can cause board breakage upon stress; they cannot be used in products prone to extensive vibrations.

Furthermore, rigid printed circuit boards cannot bend, so they cannot be used in product housings that require circuit board bending over curves.

Flexible Printed Circuit Boards

Flexible Printed Circuit Board

Flexible PCBs are no less than innovation. They have enabled the development of flexible circuits that can bend and even fold up to 360 degrees.

Like other types of printed circuit boards, flexible boards are also made of the substrate and conductive layers.

But in this case, the substrate is a flexible material that has a comparatively smaller thickness.

Flexible printed circuit boards are lightweight and require less space as compared to rigid printed circuit boards.

This is because they are developed and housed in 3D planes, and their material weighs less.

Although flexible printed circuit boards look very sensitive, they are robust and highly functional.

They are typically used in gadgets, sensors, and robotic parts, and movable parts in electronics.

Flexible PCBs are also used in equipment that doesn’t move at all, but the structure has certain bends or requires a flexible circuit assembly that can fit in small spaces.

Furthermore, flexible printed circuit boards are used in devices that operate in tuff environments, especially those prone to mechanical stress.

The only disadvantage of flexible printed circuit boards is their high cost of development.

Unlike rigid PCBs, flexible printed circuit board development is expensive unless they are developed in bulk quantity.

Furthermore, the manufacturing of flexible printed circuit boards is not simple; it is possible only on advanced equipment.

Rigid-flex Printed Circuit Boards

Flex-Rigid Printed Circuit Board

Rigid-flex PCBs are a hybrid version of rigid PCBs and flexible PCBs.

They are developed with both flexible and rigid parts, which gives them the characteristics of both rigid PCBs and flexible PCBs.

They are widely used in applications where a strong assembly is needed for the circuit, but flexible connections are required between the circuit segments.

The construction of rigid-flex PCBs is not different from rigid and flexible PCBs.

The flexible part is made just like flexible PCBs, and the structure of the rigid part is made like the rigid PCBs.

However, the connection between both parts is complicated; they are connected through holes.

The most significant benefit of rigid-flex PCBs is their ability to both bend and offer a robust assembly for the components.

They are widely used in sensitive electronic devices. Rigid-flex printed circuit boards can serve the functions of both rigid PCBs and flexible PCBs.

However, as rigid-flex PCBs are made of both flexible and rigid parts, their manufacturing is more complicated than rigid PCBs and flexible PCBs.

High-frequency Printed Circuit Boards

High Frequency Printed Circuit Board

High-frequency PCBs refers to the rigid PCBs and flexible PCBs that are developed for high-frequency circuits.

Material-wise high-frequency PCBs are usually the same as rigid and flexible PCBs; their design and development differ.

High-frequency printed circuit boards are FR4-grade glass-reinforced epoxy laminate, polyphenylene oxide (PPO) resin, and Teflon.

High-frequency boards’ design is different because at high-frequency, the signals behave differently, and high-frequency circuits cannot function properly on conventional boards.

The dielectric constant of high-frequency PCBs significantly impacts their performance; the smaller the dielectric constant higher the signal strength.

Furthermore, Unlike conventional circuits, high-frequency circuits are prone to parasitic signals, which is why high-frequency printed circuit boards are frequently grounded using via.

Evidently, the material selection and circuit designing for high-frequency printed circuit boards are far more complicated than conventional PCBs.

Most of the high-frequency printed circuit boards are designed for circuits that operate beyond 500MHz.

These PCBs are widely used in wireless communication applications. However, the design and development of high-frequency printed circuit boards involve much more factors than conventional.

Aluminum Printed Circuit Boards

Aluminum Printed Circuit Board

Unlike conventional PCBs, Aluminum PCBs use aluminum as the base material, which gives them extensive strength.

Aluminum printed circuit boards are widely used in applications that require a high degree of mechanical strength for circuit assembly.

Aluminum PCBs are most commonly used in high-power electronics such as LED light strips and power supplies.

These PCBs are suitable for circuits requiring constant heat dissipation as the aluminum back works as an excellent heat dissipater.

Unlike conventional boards, aluminum PCBs are less likely to degrade by thermal expansion; their layers do not easily fall apart.

This property makes them suitable for circuits that are prone to high temperatures.

How to Choose a Suitable Printed Circuit Board?

When choosing a suitable printed circuit board, the designers consider certain factors such as design size, mechanical strength, flexibility, weight, heat, and cost.

PCB type is chosen as per the circuit design and the environment in which PCB has to operate.

For example, complex circuits that cannot be assembled on a short PCB and need to bend can be built on multi-layer flexible PCBs.

Similarly, for circuits that require a robust and lightweight base and excessively generate heat, aluminum PCBs are most suitable.

However, for high-frequency circuits with a strong base, high-frequency rigid boards are the best option.

This is how the circuit design significantly impacts the PCB selection.

It is essential to understand that apart from the technical aspects of electronics, the designers have to consider the cost and feasibility.

For example, flexible PCBs are costly, and their development is complicated as compared to rigid boards.

But in some cases, flexible boards are a more suitable option since they are lightweight and can fit in small spaces, reducing the overall size of the product. In such cases, flexible printed circuit boards are a more suitable option.

Evidently, all the types of printed circuit boards and their selection process plays a vital role in the reliability and durability of electronics.