As the need for high-performing and miniaturized electronics has increased, the demand for dense and small-sized PCBs has also swollen. So, circuit boards have become smaller than before, are available in multiple designs, and can be tailored to fit specific requirements. Therefore, various multi-layered circuit boards have been developed, including 4-layer PCBs.
4-layer PCBs are a common type of multilayer PCBs that serve several purposes. Are you interested in learning more about them, particularly their stack-up design and types? What are their advantages, and how do they compare to 2-layer PCBs? This article will take you through all this.
What are 4-Layer PCBs?
As their name suggests, 4-layer PCBs contain four conductive copper layers. Nevertheless, they are not that simple as many people think. Since these layers are for conducting electrical signals, they are classified into the outer layers (the top and bottom layers) and the two internal layers.
The external layers connect the mounted components and route them to the inner layers. Likewise, the internal layers route electrical signals and power planes. The 4-layer PCB layout functions well because it simplifies component connections, signal transmission and minimizes EMI emissions. Besides, it has high electromagnetic compatibility.
4-Layer PCB Stack-up Design
A multilayer circuit board contains three or more conductive layers, where the inner layers are for conducting signals or power. While it is possible to create a three-layer PCB with a power plane, basically, a 4-layer board, illustrated in the diagram below, is most likely the smallest stack-up with a power plane.
4-layer PCB structure
As demonstrated above, a 4-layer stack-up design contains two inner layers, meaning the PCB makes good use of blind vias. One of the inner layers is often for conducting signals, and the other acts as a ground plane. Nevertheless, both inner layers can serve as ground planes to tap into the Electromagnetic Interference (EMI) benefits of parallel layering.
The other 4-layer PCB stack-up alternative makes use of power and ground planes. But it is recommendable to design two inner signal layers next to each other. Some applications require several power planes, but this presents some challenges, as discussed in the next subtopic.
4-Layer PCB Power Plane Design Challenges
When developing any multilayer PCB, you should apply some design tips to ensure a high-quality final product. These include designing the stack-up symmetrically and reducing the space between the ground and power planes. Sticking to such tips presents challenges for 4-layer PCB designs, as discussed below.
Multilayer Power Planes
To integrate high functionality into boards, you may be required to use components with various voltage level needs. This brings major power integrity (PI) issues, especially in the presence of one power layer. The recommended way of solving this problem is subdividing the power plane into several portions. But you must take account of current needs via number and placement to ensure that every component is sufficiently powered.
Multilayer Signal Types
Reducing the board size implies that you are using several types of signals. For instance, you can broadcast the power, digital, and radiofrequency signals through one board. The best solution is to design inner signal layers. Nevertheless, this solution is not ideal for a 4-layer PCB with a power plane because the other inner layer should act as a ground plane. If you apply a ground plane, it won’t be easy to reduce EMI and ensure the highest signal quality when creating like signals.
In 4-layer PCBs, you can only meet the symmetry requirement by developing two inner power planes. This is beneficial when several power planes are required, particularly in 2-sided boards containing upper and lower components. But you will depend on traces to rip the benefits.
4-layer PCBs display a high heat dissipation factor in 2-layer designs. You can use plane partitions and several vias to facilitate heat dissipation while meeting power needs in 4-layer PCBs experiencing heating problems.
The Difference Between a 2-Layer PCB and a 4-Layer PCB
Since 2-layer boards are common multilayer boards, it is good to see how they compare with their 4-layer counterparts. Like other multilayers PCBs, these two types of PCBs enable connections on both sides of the board.
The major difference between 2-layer and 4-layer PCBs lies in their stack-up. With 2-layer PCBs, they basically contain a top and lower layer. Regarding PCB design, 2-layer boards more transmitter pattern space compared to single-layer boards. Furthermore, that space is still small than that of a 4-layer PCB.
When it comes to cost and functionality, 4-layer PCBs are better than 2-layer PCBs. Some feel that 2-layer PCBs have more functions, but there is no big difference between them. This is why PCB experts often say that 4-layer boards and 2-layer boards are ideal in performing their job well. However, 4-layer PCBs are a bit expensive to manufacture since they are more sensitive and complex.
The Advantages and Disadvantages of 4-Layer PCBs
4-layer PCBs have two extra routing layers for signals, facilitating board miniaturization and complex device integration.
Secondly, 4-layer PCBs are beneficial to designers who design for manufacturability. Commercial electronics must be certified by various authorities. The common PCB regulations include emissions that fundamentally require PCBs not to emit radioactive components for a certain period. 2-layer PCBs face emission control challenges, but 4-layer boards apply power and ground plane protection to absorb the radiated trace emissions.
Thirdly, 4-layer circuits facilitate internal signal routing within the stacks and contain top and bottom ground planes. This arrangement makes signal routing easier as the power and ground planes can be eliminated from the routing layers to create more space for signals.
4-layer boards have disadvantages that make them undesirable in some applications. First, they are a bit expensive, making them undesirable for simpler use cases. Secondly, 4-layer boards can conceal traces in their internal layers, complicating the circuit debugging process.
Applications of 4-Layer PCBs
If you plan to use your PCBs in complex equipment like computers, smartphones, and heart monitors, multilayer boards will serve you well. Multiple PCB layers facilitate complex applications. Having many layers enables more circuitry for complex use cases. Below are the common applications of 4-layer boards.
Medical equipment: Electronics have become an integral part of the medical industry, finding applications in each corner of the industry from treatment to diagnosis. 4-layer boards are widely used in the medical space because of their miniaturized sizes and high functionality. Some medical devices that commonly use 4-layer PCBs include X-ray machines, heart monitors, testing machines, and CT scans.
Consumer electronics: These are devices we often use in our daily life, like smartphones and microwaves. Consumer electronics have circuit boards, but most of them contain multilayer boards instead of single-layer PCBs. This is because the current consumers want multi-purpose equipment that integrates well with their daily lives. These gadgets range from universal TV remotes to smart wearables.
Computer electronics: In the computer world, essential components like motherboards use multilayer boards because of their small sizes and super functionality. In this industry, performance is a preferred trait to cost. Therefore, 4-layer boards are widely used.
Telecommunications: Telecommunication devices widely use 4-layer PCBs in various applications, like signal broadcast, GPS, and satellite use cases, primarily because they are more durable and highly functional. Circuit boards for telecommunication use cases are commonly applied in mobile gadgets and outside towers, which require durable and high-performing boards.
Industrial: The four conductive layers in 4-layer PCBs make them ideal for the use case where rough handling is often experienced, e.g., in industrial controls. These boards are widely applied in the manufacturing process to control machines because of their miniaturized sizes, high durability, and performance.
Military and defense: Because of their durability, performance, and low-weights, 4-layer boards are widely applied in high-speed military equipment. They are also ideal because the defense sector is shifting towards highly compact designs, and miniaturized boards create more space for mounting extra components.
Automotive: This industry has become more reliant on electronics, especially with the invention of electric cars. Electronic devices control GPS, onboard machines, headlight switches, and engine sensors. The features of multilayer boards, like small sizes, high performance, and durability, make them ideal for use in automotive electronics.
Aerospace: Like the automotive industry, the aerospace sector requires small and high-performing devices to function. From command center computers to onboard computers, the aerospace circuit board applications should be highly reliable and durable to withstand the atmospheric stress experienced during flights. Multilayer boards have several protective layers that prevent atmospheric conditions from damaging connections.
Generally, 4-layer boards will help you minimize your design, increase its EMI performance, and facilitate complex routing. This is why they are widely applied in almost every industry.
Choose MKTPCB as Your 4-Layer PCB Manufacturer
The modern world is run by electronics that provide various features, which were technologically unimaginable half a century ago. Most of these developments are a result of the possibilities offered by multilayer circuit boards.
If you need a 4-layer board for your next project, it is advisable to partner with a reliable PCB manufacturer, like MKTPCB. We are among the leading manufacturers of 4-layer PCBs located in Shenzhen, China. Apart from 4-layer PCBs, we also deal with other types of multilayer boards at competitive market prices. Our products are RoHS compliant and meet high-quality standards. Kindly contact us today to learn more about our products and services.