Printed circuit boards are commonly seen in modern-day electronic and electrical appliances that are comprised of one or more insulating layers and copper layers. Planning the design of these multilayer PCBs is one of the important aspects to achieve a better electrical performance of the signal transmission. Poorly designed substrate and wrong choice of selected materials can degrade the performance to increase emissions and crosstalk to make it more susceptible to external noise.
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A properly designed PCB board substrate can effectively reduce electromagnetic emissions, and crosstalk and also improve the signal integrity to provide low inductance power. The external noise needs to be suppressed at the source than trying to eliminate the noise once the product has been manufactured. This proper design of multilayer PCBs can increase immunity to RF fields by a factor of 10 or more, compared to the double-sided boards.
But overall, multilayer boards are expensive and harder to troubleshoot than any other simple double-sided printed circuit board. However, multilayer PCBs offer better shielding and signal routing, and there are more layout options for this kind of board design. In comparison to single or double-sided boards, multilayer PCBs provide extra density to route power and signal tracks. With this, the components can be packed tightly on the board to offer a more compact design.
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In simple words, Multilayer PCB is a printed circuit board with more than two layers and has a minimum of three conductive layers of conductive material or copper layer. When looking at a multilayer PCB, the top and bottom layers look similar to a double-sided PCB but they have more layers on both sides of the core. These layers are interconnected with copper-plated holes and there can be more layers as we have witnessed up to 40 layers. The active and passive components are placed on the top and bottom layers of the multilayer PCB while the inner stacked layers are used for routing.
As multilayer PCBs can accommodate more electronic components, they have been widely used in modern-day electrical appliances with variants ranging from four to twelve layers. Several applications, such as smart devices require between four to eight layers, while smartphones can use up to twelve layers. While manufacturing multilayer PCBs, designers choose an even number of layers over odd as laminating an odd number of layers can make the circuit complex and also result in high cost.
In a typical four-layer stack up, to improve the electromagnetic compatibility (EMI) performance, the signal layers should be spaced as close to the planes and use a large core between the power and ground plane. The tight coupling between signal trace and ground plane often reduces the plane impedance which further reduces the common-mode radiation from the cables connected to the printed circuit board. Also, the close trace to plane coupling will decrease the crosstalk between traces.
As we increase the number of layers to twelve, the high layer count boards require thin dielectric and hence they automatically have tight coupling between the layers. They are often used for high-speed electronics to deliver improved EMI performance and signal integrity. Interestingly, there is no limit to the number of layers that can be fabricated in a multilayer PCB. But as the layer increases, the board thickness also increases to accommodate the minimum thickness of materials used.
Stacked PCBs
The first step toward the multilayer PCB manufacturing process is to design the layout of the board using any of the PCB designing software, for example, Eagle, Proteus Altium, and KiCAD. Once the design is ready, it is important to make the inner layer core and laminate with desired thickness with copper foil, dry film resist and UV light. The next step in the design workflow is the lamination which includes the inner layer core, prepreg sheets, and copper foil sheets. Next is to apply pressure, heat and vacuum using a heated hydraulic press and it is important to make sure that there is no air trapped between layers. Once cured, resins from the prepregs join the sheets, core and foil to form a multilayer PCB.
In a multilayer PCB design, the designer needs to dedicate one layer to a ground plane and another to the power plane. For digital-only PCBs, the designer can also dedicate the entire power layer and if there is space on the top and bottom layer, that can be used to route any additional power rail tracks. The power layers are always in the middle of the board with the ground closer to the top layer. Once the power is taken care of on the inner layers, the remaining space is available for signal tracks that are routing. For example, in a six-layer stack up, there will be four signal routing layers and two layers dedicated to power.
Multilayer PCBs have two reference planes and a signal via. The signal via allows the electrical signal to flow through all the stacked planes which are used for routing. The stitching via is connected to one of the planes next to the signal via and provides a reduction in area for the signal flow. These types of PCBs have several different options of vias to improve the routing density' commonly referred to as standard, blind, and buried.
In simple words, via refers to an electrical connection between different layers on the printed circuit board. These are seen as small holes on the PCB that crosses two or more adjacent layers. Vias are different from plated through holes as they are used for electrical connection of through-hole components on the PCB and usually have larger dimensions than the vias. The via hole is covered with copper to form an electrical connection in the insulating material that separates the different layers of the printed circuit board. Depending on the application requirements, the board may require vias that cross all the layers of the stock or only one of the outermost layers. As mentioned earlier, there are three types of vias' standard (also referred to as through-hole via), blind, and buried.
PCB vias
The standard vias are seen to pass all the layers of the printed circuit board to connect the top, bottom and inner layers. They have large dimensions than the other types of vias and are simpler to make as there is no restriction on the drilling process.
The blind vias typical are drilled from the outside layer of the printed circuit board to the inner layers and do not make a hole on the other side of the board. They are referred to as 'blind' because the hole cannot be seen from another side of the board. In the case of multilayer boards, these types of vias can introduce challenges to manufacturing as the designer needs to precisely determine when to stop the drilling process to achieve the desired degree of depth. They are used for increasing the number of connections between the outer and inner layers of the printed circuit board.
The buried vias are used to connect two or more inner layers of the printed circuit board and hence are not visible on either outer layer. In the case of multilayer PCBs, the internal plating of the buried vias must be completed before applying the two outer layers of the board. Buried vias can increase the manufacturing cost as it requires more precision to design.
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Even though the design process for multilayer PCB is complex and requires domain expertise, they possess several benefits that make them widely used in modern-day advanced electronic devices and electrical appliances. Here are some of the benefits of multilayer printed circuit boards:
Reduced form factor: Multilayer PCBs have used evolving manufacturing processing and advanced design rules to reduce the size of the boards with maintaining the same functionalities. Multilayer PCBs are also used in smartphones and electronic gadgets that require small size, and hence they are easily adapted for the growing demand for electronic wearables.
Advanced manufacturing techniques to result in lightweight boards: These multilayer printed circuit boards are manufactured to achieve less weight and can be used in wearable smart devices. One of the highlighted reasons for the reduction in weight is the elimination of multiple connectors required to interlink separate double-sided PCBs of a multilayered design.
Production of multifunctionality board with high quality: There is a tremendous amount of work done in the design and manufacturing process to offer multifunctionality in the small form factor printed circuit board. To be used in smartphones, they possess several functionalities which are usually not offered by a single-layer board due to its limitations.
More durability and flexibility for long-term use: This kind of printed circuit board is designed to withstand more weight and is also able to handle the heat and pressure used to bind the layers together. Also, they provide flexibility to be tweaked according to the applications and do not require a complete re-design.
Single connection point: Multilayer PCBs are designed to work on a single connection point than the multiple connection points required to use multiple single-layer PCBs.
Even though there are many benefits of using multilayer PCBs, you should also be aware of the downsides of the manufacturing and designing process. Here is a list of disadvantages of multilayer PCBs:
Elevated cost of production: Multilayer PCBs are more expensive than single and double-sided PCBs at every stage of the manufacturing process. There is an increased amount of labour work and advanced design along with the pricey assembly machinery.
Complex design process: It takes an increased amount of hours for designing multilayer PCBs and also the designer needs to follow many design rules. The choice of lamination and substrate also depends on the type of applications and the number of active and passive components to be mounted.
Required domain expertise: Multilayer PCBs cannot be designed by anyone as they require experience in CAD tools and an understanding of design rule checks. Due to several challenges in the design process, domain expertise is essential.
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PCB applications
Modern-day consumer electronic appliances: As we have mentioned earlier, smartphones and smart devices use multilayer PCBs due to their small form factor and multifunctionality.
Telecommunication industry: Network appliances and transmission devices use multilayer PCBs due to their durability and flexibility to adapt to outdoor and indoor environments.
Manufacturing industry and production line: With its durability comes the capability to be used in extreme industrial setups to withstand pressure, heat, and high temperature. Also, the multifunctionality and small form factor are other reasons for its extended adoption.
Medical devices and the healthcare industry: Medical equipments require precise functioning for treatment and diagnosis. Multilayer PCBs are used in the medical industry due to their less weight and extensive robust functionalities.
Military and defense: Durability and low weight are essential factors to be used in military and defense. Multilayer PCBs provide compact designs with small size boards for more room for other components and custom functionalities.
Automotive and aerospace systems: These industries are dependent on precision and extreme conditions. Multilayer PCBs can withstand extreme operating conditions and do not damage the product to maintain its quality and functionality.
Multilayer PCBs are normal electrical boards that consist of two or more inner layers to the outermost layers considered as power and ground plane.
Designing multilayer PCBs is a complex task and requires domain expertise to achieve improved electrical performance and reduce external noise.
With high production costs comes the multifunctionality features, and this is the trade-off designers should be aware of.
There are several advantages to the production of multilayer PCBs, including small form factor, multiple functions, lightweight production, durability, and flexibility.
There are a few downsides as well, which are the elevated cost of production, requiring domain expertise to design the boards, and a complex design and manufacturing process.
The multilayer boards are used across a wide range of industries, including consumer electronics, telecommunications, defense and military, etc.
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[2] Available online: https://smtnet.com/library/files/upload/Multilayer-PCB-Stackup.pdf; Accessed. July 8, .
[3] Available online: http://www.idc-online.com/technical_references/pdfs/data_communications/Multilayer_PCB.pdf; Accessed. July 8, .
[4] Available online: https://www.oki.com/en/otr//n216/pdf/otr-216-R07.pdf; Accessed. July 9, .
[5] Available online: https://narasimmamohan.files.wordpress.com//09/design-of-multilayer-pcbs-smd-mounting-techniques.pdf; Accessed. July 10, .
[6] Available online: https://www.analog.com/media/en/training-seminars/design-handbooks/Basic-Linear-Design/Chapter12.pdf; Accessed. July 10, .
[7] Available online: https://server.ibfriedrich.com/wiki/ibfwikien/images/d/da/PCB_Layout_Tutorial_e.pdf; Accessed. July 10, .
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.
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.
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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, but the largest one ever made was 129 layers thick. 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 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.
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.
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.
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.
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.
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.
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
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 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.
To determine whether you need single-layer or multi-layer printed circuit boards, you need to consider the needs of your project and which type best meets them. Ask yourself these five questions:
1. What level of functionality do I need? If it's more complicated, you may need multiple layers.
2. What is the maximum size the board can be? Multi-layer boards can fit more functionality into a smaller space.
3. Is durability a priority? If so, go with multi-layer.
4. What is my budget? For more modest budgets, single-layer boards work best.
5. How quickly do I need the PCBs? Single-layer printed circuit boards have a shorter lead time compared to multi-layer printed circuit boards.
You will also have to deal with more technical questions regarding requirements, such as the operation frequency, density and signal layers you need. Determining the answers to these questions will help you figure out if you need a board with one, two, four or more layers. For more information about these specifications and other tips on choosing a PCB design, check out our blog post on the topic.
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