Single-Layer vs. Multi-layer PCBs

As a preliminary step before designing a printed circuit board, you need to decide whether you'll use a single-layer or multi-layer PCB. Both design types are common in a variety of everyday devices. The kind that's right for you depends on the project you're using it for. More complex devices typically use multi-layer boards, while simpler ones can benefit from single-layer. This article will explain the essential differences between them, as well as how to choose the correct type for your project.

Single-Layer vs. Multilayer PCBs: What's the Difference?

You can likely guess what the significant difference is between these two types of PCBs based on their names. Single-layer boards have just one layer of base material, also known as a substrate, while multi-layer PCBs have multiple layers. Once you look closer at the three primary types of PCB boards, you'll see there are many other differences in how they're constructed and how they function.

1. Single-Layer PCBS

Single-layer boards, sometimes called single-sided boards, have components on one side of the board and a conductor pattern on the opposite side. They have just one layer of conductive material, typically copper. A single-layer board is comprised of a substrate layer, a conductive metal layer and then a protective solder mask and silk-screen. You'll find single-layer boards in many simpler electronic devices.

2. Double-Sided PCBs

You can also use a double-layer or double-sided board, which has more layers than a single-layer board but fewer than a multi-layer. Double-sided PCBs, like the single-sided variation, have one substrate layer. The difference is that they have a layer of conductive metal on both sides of the substrate.

Circuits and components on one side of the board are connected to those on the other side through one of two methods:

• Through-Holes: Through-holes are small holes drilled through the board that wires, called leads, are fed through, then soldered to the correct component.

• Surface Mounts: These PCBs use leads soldered directly to the board. The board itself becomes the wiring surface for the components, which allows the circuits to take up less space.

3. Multi-Layer PCBs

Multi-layer PCBs are made of three or more double-sided boards stacked on top of each other. Theoretically, they can contain as many boards as you can need. Typically, they have an even number of between four and 12 layers — odd amounts can cause problems such as warping and twisting post-soldering.

Each substrate layer in a multi-layer board has a conductive metal on both sides of it. The boards are joined together using a specialized kind of adhesive, and there is an insulating material between each board. On the very outer edges of the multi-layer board, you'll find solder masks.

Paths known as vias allow the different layers to conduct to each other. These paths fall into three groups:

• Through-Hole: Go through every layer of the board

• Blind: Connect an outer layer to an inner layer

• Buried: Connect two inner layers, rendering them invisible from the outside

Multi-layer boards typically appear in more complex devices that require a high number of connections.

Single-Layer PCB Advantages

Single-Layer PCBs have several advantages over other board types that, depending on the requirements of your project, might make them your PCB of choice. These include:

• Lower Cost: Because single-layer PCBs are simpler than double-sided and multi-layer PCBs, they require fewer resources, less time and less expertise to design and produce. This makes them less expensive. If it's possible to use a single-sided board without sacrificing quality and performance, most people do because of the economic advantages. When it comes to single- vs. multi-layer PCBs, lower cost is one of single-sided boards' significant benefits.

• Simpler Design and Production: Single-sided boards are relatively simple and are also very common, which means most designers can easily design them, and most manufacturers can build them without any issues. The design and production processes will be easy compared to multi-layer printed circuit boards and produce consistently positive results. Almost any PCB company can produce single-layer boards because of their simplicity.

• High Volume: The ease with which these boards can be produced means you can order them at high volumes without running into problems. Because higher amounts will lower the price per board even more, bulk ordering is one of the best ways to get the most value out of single-sided PCBs.

• Short Lead Time: Single-layer boards can be manufactured quickly due to their simplicity and the fact that they require fewer resources than multi-layer PCBs. This makes them the perfect choice for instances when you need PCBs quickly even with high-volume quantity.

Single-Layer PCB Disadvantages

Despite their cost advantages and other perks, single-layer boards are not the right choice for every project due to the limitations they have, which include:

• Simplistic Design: The simplicity of single-layer boards' is one of their biggest benefits, but it's also a substantial limitation. For more complex devices that require a higher number of components and connections, a single layer does not provide enough space or power. If wires cross each other, the device won't function properly, so it's critical that the board has enough space to accommodate everything. More complex designs just can't fit on single-sided PCBs.

• Slower Speed and Lower Operating Capacity: The limited number of connections on these boards also affects their power and speed. These less-dense designs are not as robust as those with more circuits and have a lower operating capacity. They might not have enough power for some applications.

• Larger Size and Higher Weight: To add capabilities to a single-sided board, you need to expand its dimensions rather than add another layer, as you could with you a multi-layer PCB. You could use multiple separate boards, but one multi-layer board could likely handle the same requirements. Increasing the size or number of boards in a device also increases your final product's weight.

Single-Layer PCBs: Weighing the Pros and Cons

To determine whether a single-layer PCB is right for you, you need to consider the requirements of your project and whether single-sided boards have the capabilities you need to meet them. For simpler devices, they're usually the board of choice due to their low cost and fast production times. For more complex projects, though, they often don't provide enough functionality.

Weigh the advantages and disadvantages of single-layer PCBs before deciding to use them. To summarize, the pros and cons of single layer PCBs include:

Pros:

• Lower cost

• Simpler design and production

• Ability to be produced at a high volume

• Shorter lead time

Cons:

• Too simplistic for complex projects

• Lower operating capacity

• Slower speed

• Larger size

• Higher weight

Are single-sided PCBs the right kind of component for you? If they meet your project's criteria and the pros above outweigh the cons, they likely are.

Single-Layer PCB Applications

These boards are popular choices for a wide variety of electronics due to their low cost and the relative ease with which they can be produced. Although multi-layer boards are catching up as electronic get more complex, single-layer boards have historically been the most common type. They often show up in devices that have one specific function and don't require storing large amounts of data or access to the internet, although this isn't always the case.

You'll find single-layer PCBs in many small household appliances, such as coffee makers. They're also the technology behind most calculators, radios, printers and LED lights. Simpler storage devices like solid state drives often use single-sided PCBs, as do components like power supplies and many different types of sensors.

Multi-Layer PCB Advantages

Although single-layer boards have their advantages, multi-layer designs are more beneficial for some applications. For some devices, it's even necessary to have multiple layers. The benefits of more complex multi-layer PCBs include:

• Useful for More Complicated Projects: Devices that are more complex and involve more circuits and components often require the use of a multi-layer PCB. If it needs more circuits than can fit on a single board, you can add space by adding layers. Having multiple boards ensures there is ample room for connections, making it ideal for more advanced devices. Devices with many different uses and advanced capabilities, such as smartphones, require this level of complexity.

• High Quality: Multi-layer boards require more planning and intensive production processes, so they are typically of a higher quality than other types of boards as a result. Designing and producing these boards requires more skill and more advanced tools than simpler components do, increasing the likelihood you'll get a top-quality product. Many of these designs include advanced controlled impedance features and electromagnetic interference shielding, further improving performance.

• Added Power: Because of the increased circuit density of multi-layer PCBs, they're more powerful than less intricate designs. They have a higher operating capacity and can run at higher speeds,  which is often necessary for the advanced devices they power and allows for improved performance.

• Increased Durability: Having more layers means the board is thicker and, therefore, more durable than single-sided PCBs. This is another reason adding functionality through additional layers is preferable to increase the dimensions of a single layer. This enhanced durability means the boards can withstand harsher conditions and often last longer.

• Smaller Size and Lighter Weight: Multi-layer PCBs achieve this enhanced durability while still maintaining a relatively small size and low weight. Because they stack layers on top of each other, you can squeeze more functionality into a tighter space than with other boards. This smaller size also translates to a lower weight. A single-layer board would have to be quite large to match the functionality of a multi-layer board. You could potentially even match it using multiple single-layer boards, but that would also increase the size and weight of your final product.

• Single Connection Point: Using multiple PCB components would require multiple connection points. Multi-layer boards, on the other hand, are designed to work with a single connection point, simplifying the design of the electronic device and further reducing the weight. When deciding whether to use more than one single-sided board vs. just one multi-layer printed circuit board, the multi-layer board is usually the best choice.

Multi-Layer PCB Disadvantages

The enhanced functionality and other benefits that multi-layer boards provide do, however, come at a price. These drawbacks mean they might not be the ideal choice for every type of project. They include:

• Higher Costs: Designing and manufacturing boards with multiple layers is more expensive than producing ones with only one or two layers. It requires more resources, more time and more skill, which drives up the price. Always make sure the benefits of a multi-layer component outweigh the costs. If having more than two layers is not necessary, you might want to stick with a single-layer PCB.

• More Complicated Design and Production: Designing and producing multi-layer boards is a more complicated and involved process than making single-layer boards. This means you need highly skilled designers and manufacturers who have specialized equipment. You're also more likely to experience difficulties throughout the process, especially if you don't have the necessary resources available to you.

• Less Availability: Because of the specialization multi-layer boards require, not every manufacturer or supplier can reliably produce or provide them. You might realize it's harder to find the right company to work with for designing, manufacturing or repairing a board with a high number of layers. If a board needs repairs, it might also be more difficult to find someone capable of fixing it.

• Longer Lead Times: Designing and producing multi-layer boards also takes more time than making single-layer boards. There are more parts to consider, which all have to be secured to each other to form one board out of the various layers. These processes are also more involved, which adds to the lead time. If you need your boards made quickly, using multi-layer PCBs might not work for you. If a mistake occurs during the production process or you want to change the design, reworking can be extremely time-consuming and may be impossible without replacing parts, increasing material costs.

• More Complex Repairs: Multi-layer PCBs are relatively reliable, but if something does go wrong, the complexity of their design can make repairs more difficult. If a problem occurs with an electronic component or the board gets physically damaged, it can be harder to identify the problem because some of the inside layers and the vias that connect them aren't visible from the outside. The sheer number of components on the board also make repairs more challenging and time-consuming.

• Multi-Layer PCBs: Weighing the Pros and Cons

Are multi-layer printed circuit boards perfect for your electronic device? If the device is on the more complex end of the spectrum, they very well may be. Be prepared, though, to pay extra for the increased functionality and other advantages. Consider the benefits and drawbacks of choosing multi-layer PCBs, as well as the needs of your project and the resources you have to devote to procuring the boards. The pros and cons of multi-layer PCBs include:

Pros:

• Ability to handle more complex functionality

• Higher quality

• More power, operating capacity and speed

• Enhanced durability

• Smaller size and reduced weight

• Single connection point

Cons:

• Higher costs

• More complicated design and production

• Limited availability

• Longer lead times

• More complex repairs

Multi-Layer PCB Applications

As technology becomes more advanced, multi-layer PCBs are becoming more common. The complex functionality and smaller size of many of today's electronic devices necessitates the use of multiple layers in their circuit boards. A range of devices across industries use multi-layer boards, especially those with several functions and more complex capabilities.

Multi-layer printed circuit boards show up in many computer components, including motherboards and servers. Computerized devices from laptops and tablets to smartphones and smartwatches use these types of boards. Smartphones typically require around 12 layers. The systems that allow electronics like smartphones, laptops and GPS devices to function, such as cell phone towers and satellite technologies, also include multi-layer boards because of the advanced functionality they require.

Devices that are less complicated than smartphones and signal towers but too complex for a single-sided printed circuit board typically use between 4 to 8 layers. Examples of these types of products include household items like microwaves and air conditioners, which increasingly utilize multi-layer technology.

Medical devices also often run on boards with more than three layers because of the reliability, small size and lightweight design they require. Multi-layer printed circuit boards appear in X-ray machines, heart monitors, CAT scan equipment and many other applications.

The automotive and aerospace industries are also increasingly using electronic components that need to be both durable and lightweight, making this type of PCB a perfect fit. These components must be able to withstand wear, heat and otherwise harsh conditions. Onboard computers, GPS systems, engine sensors, headlight switches and more components utilize these boards.

PCBs with high numbers of layers are also standard in the industrial industry. More and more industrial machines have computerized components and often come equipped with sensors, controls and other parts that require PCBs. This equipment needs advanced functionality, reliability and durability due to the harsh conditions of many industrial facilities.

For similar reasons, multi-layer PCBs play a role in many military applications, weather analysis equipment, alarm systems, atomic accelerators and a multitude of other electronic equipment types.