While PCBs for simple electronics with limited functions are usually composed of a single layer, more sophisticated electronics, like computer motherboards, consist of multiple layers.   These are what are called multilayer PCBs. With the increasing complexity of modern electronics, these multilayer PCBs have become more widespread than ever before, while manufacturing techniques have enabled them to size down significantly.

What Is a Multi-layerPCB?

The definition of multilayer PCB is a PCB that is made with three or more conductive copper foil layers. These appear as several layers of double-sided circuit boards, laminated and glued together with layers of heat-protective insulation between them.  The entire construction is arranged so that two layers are placed on the surface sides of the PCB to connect to the environment.  All electrical connections between the layers are achieved with vias such as plating through holes, blind and buried vias.    Application of this method then leads to the generation of highly complex PCBs of varying sizes.

The multilayer PCB came into being due to the evolving changes in the electronics industry.  The functions of electronics have become progressively more sophisticated over time, requiring more complex PCBs. Unfortunately, PCBs were limited by problems like noise, stray capacitance and crosstalk, and therefore needed to follow certain design constraints.  These design considerations made it difficult to get a satisfactory level of performance from a single or even double-sided PCB - thus the multilayer PCB was born.

While they do tend to be more expensive and labor-intensive to produce, multilayer PCBs are becoming an essential part of modern technology. This is primarily due to the host of benefits they offer, particularly in comparison to single and double-layer varieties.

MultilayerPCB Benefits

From a technical point of view, multilayer PCBs present several advantages in design. These benefits multilayer PCBs present include:

• Small Size: One of the most prominent and lauded benefits of using multilayer PCBs lies in their size. Because of their layered design, multilayer PCBs are inherently smaller than other PCBs with similar functionality. This presents a major benefit to modern electronics, as the current trend is working toward smaller, more compact yet more powerful gadgets like smartphones, laptops, tablets and wearables.

• Lightweight Construction: With smaller PCBs comes less weight, especially as the multiple connectors required to interlink separate single and double-layered PCBs are eliminated in favor of a multilayered design.This, again, is beneficial for modern electronics, which are geared more toward mobility.

• High-Quality: Due to the amount of work and planning that must go into the creation of multilayer PCBs, these types of PCBs tend to be better in quality than single and double-layer PCBs.They also tend to be more reliable as a result.

• Increased Durability: Multilayer PCBs tend to be durable by their nature. Not only do these multilayer PCBs have to withstand their own weight, but they must also be able to handle the heat and pressure used to bind them together. On top of these factors, multilayer PCBs use multiple layers of insulation between circuit layers, binding it all together with prepreg bonding agent and protective materials.

• Enhanced Flexibility: Though this does not apply to all multilayer PCB assemblies, some do use flexible construction techniques, resulting in a flexible multilayer PCB.  This can be a highly desirable trait for applications where mild bending and flexing may occur on a semi-regular basis. Again, this does not apply to all multilayer PCBs, and the more layers incorporated into a flexible PCB, the less flexible the PCB becomes.

• More Powerful: Multilayer PCBs are extremely high-density assemblies, incorporating multiple layers into a single PCB.  These close-quarters enable boards to be more connective, and their innate electrical properties allow them to achieve greater capacity and speed despite their smaller size.

• Single Connection Point: Multilayer PCBs are designed to work as a singular unit, rather than in tandem with other PCB components.  As a result, they have a single connection point, rather than the multiple connection points required to use multiple single layer PCBs.  This proves to be a benefit in electronic product design as well since they only need to include a single connection point in the final product.  This is particularly beneficial for small electronics and gadgets designed to minimize size and weight.

These benefits make multilayer PCBs highly useful in a variety of applications, particularly mobile devices and high-functioning electronics.  In turn, with so many industries turning to mobile solutions, multilayer PCBs are finding a place in an increasing number of industry-specific applications.

Why Are Multilayer PCBs So Widely Used?

Much of the favoritism toward multilayer PCBs lies in industry trends.  With electronics progressing ever toward miniaturization yet multi-functional options, the internal components of those electronics must follow the same trend.  While single and double-sided PCBs have proven limited in their ability to balance size and functionality, multilayer PCBs provide a comprehensive solution.

While there are several drawbacks to using multilayer PCBs over single and double-layer options, such as increased costs, design times and production inputs, these costs are becoming more accepted in today's world.  Functionality is largely favored over cost, and people are willing to pay more for high capacity electronics.  Additionally, as the technology becomes increasingly mainstream, production techniques and machinery will eventually become less expensive, especially as new techniques arrive in the industry.