At the heart of most electronic products today, the PCB determines basic functionality through a combination of components and routing mechanisms. While most PCBs in the past were relatively simple and limited by manufacturing technology, today's PCBs are much more complex. From advanced flexible options to quirky varieties, there are many types of PCBs in today's electronics world, with multilayer circuit boards being especially popular.

　　The emergence of multilayer circuit boards is due to the development and changes in the electronics industry. Over time, electronic functions have become more complex, requiring more complex PCBs. Unfortunately, PCBs are limited by issues such as noise, stray capacitance, and crosstalk, so certain design constraints need to be followed. These design considerations make it difficult to achieve satisfactory performance levels for single- or double-sided PCBs—hence the birth of multilayer boards.

　　A multilayer circuit board is defined as a PCB made of three or more layers of conductive copper foil. They appear as several layers of double-sided circuit boards, laminated and bonded together, with thermal insulation between them. The entire structure is laid out so that two layers are placed on the surface side of the PCB to connect to the environment. All electrical connections between layers are made through vias such as plated through holes, blind vias and buried vias. Application of this method then results in the creation of highly complex PCBs of various sizes.

　　While the PCBs of simple electronic devices with limited functionality are usually composed of single-sided or double-sided circuit boards, more complex electronic devices (such as computer motherboards) are composed of multiple layers of circuit boards, which are called multi-layer PCBs. With the increased complexity of modern electronic devices, these multilayer circuit boards have become more ubiquitous than ever, and fabrication techniques have allowed them to be drastically reduced in size.

　　Multilayer circuit boards are becoming increasingly popular in electronics, and they come in a variety of sizes and thicknesses to meet the needs of their extended applications, ranging from four to twelve layers. The number of layers is usually an even number, since an odd number of layers can cause problems in the circuit (such as warpage) and it is no longer cost-effective to produce. Most applications require four to eight layers (called: multilayer boards), although applications such as mobile devices and smartphones tend to use around a dozen layers, and some professional PCB manufacturers boast of being able to produce nearly 100-layer multilayer PCB. However, multi-layer PCBs with such a multi-layer structure are extremely low cost and therefore rare.

　　While it is true that multilayer circuit boards are more expensive and labor-intensive, multilayer circuit boards have become an essential part of modern technology. This is mainly due to the many benefits they offer, especially compared to single-sided and double-sided circuit board varieties.

Read recommendations:

Aluminum substrate (double-sided)

Six-layer Immersion Gold Board (BGA)

Mobile phone board

DIP plugin

The difference between circuit board and aluminum substrate