Multilayer PCB Board introduction and Prototype Fabrication Service

Here you can learn more about the definition, laminate structure, manufacturing process, advantages, and applications of multilayer Printed circuit boards.

What is Multilayer PCB Board?

multilayer printed circuit board

Why Are Multilayer Circuit Boards Catching on?

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.

Definition of the Multilayer PCB Board

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 coats 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 plated through holes, blind and buried vias. The application of this method then leads to the generation of highly complex PCBs of varying sizes.

Multilayer Printed circuit board is an integral part of most of the electronics when it comes to the connecting number of electronic components on the board. Multilayer PCB technology helps us getting rid of the old ways of joining parts where components were joined together by the end to end wiring, resulted in covering more space and weight and unable to fulfill the requirements of more complicated designs. Experts are in a constant struggle to improve the electronic design with a compact shape, so it provides a better user experience and turns out to be less costly than its predecessors.

multilayer PCB Circuit Board

Now, you have got a clear idea of why do we need PCB. There are already different types of PCB boards available in the market, i.e., single-layer PCB board and double-layer PCB board. But, sometimes, these boards fail to deliver more complex designs because of the availability of less number of conductive layers on the board. Technology is evolving with the greater need to make devices cheap and low weight so they can meet the requirements in less cost and capable of performing more functions than using conventional ways of making electronic devices.

Multilayer PCB boards came into play intending to construct more number of conductive layers on the board than a single layer or double layer boards. Multilayer circuit boards come with a combination of a single layer or double layer board and allow connecting more electronic components in less space. These boards are made with several conductive layers with insulating material between them. Multilayer boards are mostly developed in rigid form because flexibly making multilayer boards is very difficult to achieve, and it also results in more cost than rigid boards. Instead of using flexible multilayer boards, most of the professionals prefer using combinations of single or double-sided boards that are very effective in most cases and are cheaper than flexible multilayer boards.

The development of a multilayer board depends on customers` demands. With the invention of new technology, multilayer boards can be manufactured with up to 100 conductive layers, making sophisticated design where more number of components are joined together. Smartphones are a great example of a multilayer PCB that gives the benefit of performing more functions using a single board. This refrains from spending more money on the combination of single-sided or double-sided boards because they cost heavily with no guarantee of fulfilling requirements as multilayer PCB.

Multilayer boards can be manufactured with even conductive layers or odd conductive layers on them. However, it is recommended to use multilayer PCB with even layers because it results in the simple design and helps in joining several different components on the board where board design with odd layers can be costly and pertains to intricate design, making it challenging to enter several electronic components on the board. Also, design with varied layers makes it very difficult twisting the board during the execution of the project, as odd sheets are not equally distributed over the whole board structure, which can damage the boards when they are subject to under heavyweights.

Some multilayer circuit boards are manufactured so strictly, making it very difficult for you to count the total number of layers with the naked eye. However, you still can guess the total number of segments based on the pattern of the layers and how they are laminated on the board. The number of different conductive layers on the multilayer boards can be termed as a signal, power, or ground planes. Power or ground planes are directly proportional to the number of voltage requirements on the board, and if there is a need for more than voltage supply on the board, then multilayer boards come with more than one power or ground planes.

Multilayer PCB 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 significant 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, primarily 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 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, wrapping it all together with prepreg bonding agents 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 layer PCB. These close-quarters enable boards to be more connective, and their natural electrical properties allow them to achieve higher 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 various 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.

Multilayer PCB Disadvantages

The benefits of multilayer PCBs are numerous, making them applicable to a wide variety of advanced technologies. However, these types of PCBs aren’t appropriate for all applications. Several drawbacks can outweigh multilayer PCB advantages, especially for electronics of lower cost and complexity. These disadvantages include the following:

  • Higher Cost: Multilayer PCBs are significantly more expensive than single and double layer PCBs at every stage of the manufacturing process. They are challenging to design, taking an extensive amount of time to work out any potential problems. They also require a highly sophisticated manufacturing process to produce, which makes a great deal of time and labor on the part of assembly personnel. Additionally, due to the nature of these PCBs, any mistake in the manufacturing or assembly process is prohibitively painful to rework, resulting in either additional labor costs or scrap material expenses. On top of it all, the equipment used to produce multilayer PCBs is quite expensive because it is still a relatively new technology. For all those reasons, unless small size is an absolute necessity for the application, cheaper alternatives may be a better choice overall.
  • Complicated Production: Multilayer PCBs are more challenging to produce, requiring much more design time and careful manufacturing techniques than other PCB types. This is because even small flaws in the PCB’s design or fabrication could render it useless.
  • Limited Availability: One of the most significant issues with multilayer PCBs is the expenses of the machinery needed to produce them. Not all PCB manufacturers have the funds or the necessity for this machinery, so not all PCB manufacturers carry it. This limits the number of PCB manufacturers available to produce multilayer PCBs for clients. Thus, it’s best to carefully inquire about a PCB Manufacturer’s capability in terms of multilayer PCBs before deciding it as your contract manufacturer.
  • Skilled Designer Required: As previously discussed, multilayer PCBs require extensive design beforehand. Without previous experience, this can be problematic. Multilayer boards require interconnection between layers, but must simultaneously mitigate crosstalk and impedance issues. A single problem in the design can result in a non-functioning board.
  • Production Time: With increased complexity comes more manufacturing requirements. This plays into a critical issue with multilayer PCBs’ turnover rate – each board requires a significant amount of time to produce, resulting in more labor costs. Additionally, it possibly leads to more extended periods between when an order is placed, and when the product is received, which can be a problem in some circumstances.

However, these issues do not diminish from the utility of multilayer PCBs. While they tend to cost more than a single layer PCB, a multilayer PCB claims many advantages over this type of Printed Circuit Board.

Multilayer PCB Applications

The advantages and comparisons discussed above beg the question: what’s the use of multilayer PCBs in the real world? The answer is just about any application.

For numerous industries, multilayer PCBs have become the preferred option for a variety of applications. Much of this preference derives from the continuous push across all technology toward mobility and functionality. Multilayer PCBs are the logical step in this progression, achieving greater functionality while reducing size. As such, they’ve become relatively ubiquitous, used in many technologies including:

  • Consumer Electronics: Consumer electronics is a broad term used to cover a wide range of products used by the general public. This tends to include products used daily, such as smartphones and microwaves. Each of these consumer electronics contains a PCB, but an increasing proportion of them are using multilayer PCBs instead of standard single layers. Why? Most of the reason lies in consumer trends. People in the modern world tend to prefer multi-function gadgets and smart devices that integrate with the rest of their lives. From universal remotes to smartwatches, these types of devices are relatively common in the modern world. They also tend to use multilayer PCBs for their increased functionality and smaller size.
  • Computer Electronics: Everything from servers to motherboards uses multilayer PCBs, primarily for their space-saving attributes and high functionality. With these applications, performance is one of the essential characteristics of a PCB, whereas cost is relatively low on the list of priorities. As such, multilayer PCBs are an ideal solution for many technologies in this industry.
  • Telecommunications: Telecommunication devices often use multilayer PCBs in numerous general applications, such as signal transmission, GPS, and satellite applications. The reason for this lies primarily in their durability and functionality. PCBs for telecommunications applications are often either used in mobile devices or towers outdoors. In such applications, sustainability is essential while still maintaining a high level of functionality.
  • Industrial: Multilayer PCBs do prove more durable than several other options currently on the market, making them an excellent choice for applications where rough handling may be a daily occurrence. As such, multilayer PCBs have become popular in several industrial applications, most notable of which are industrial controls. From industrial computers to control systems, multilayer PCBs are used throughout manufacturing and industrial applications to run machinery, favored for their durability as well as their small size and functionality.
  • Medical Devices: Electronics is becoming an increasingly essential part of the healthcare industry, functioning in every corner of the industry from treatment to diagnosis. Multilayer PCBs are particularly favored in the Medical industry for their small size, lightweight nature, and impressive functionality compared to single-layer alternatives. These benefits have led to multilayer PCBs being used in modern X-ray equipment, heart monitors, CAT scan equipment and medical testing devices, etc.
  • Military and Defense: Favored for their durability, functionality, and low weight, multilayer PCBs are useful in high-speed circuits, which is becoming an increasing priority for military applications. They’re also favored due to the defense industry’s increased movement toward highly compact engineering designs, as the small size of multilayer PCBs leaves more room for other components to flourish existing functions.
  • Automotive: Cars are relying on electronic components more and more in the modern era, especially with the rise of electric cars. With everything from GPS’s and onboard computers to headlight switches and engine sensors controlled by electronics, using the right kinds of components becomes increasingly essential in automotive design. This’s why many auto manufacturers start to favor multilayer PCBs over other alternatives. While they are small and durable, multilayer PCBs are also highly functional and relatively heat-resistant, making them a good fit for the internal environment of an automobile.
  • Aerospace: Like cars, jets and rockets rely heavily on electronics in the modern era, all of which must be extremely precise. From the computers used on the ground to those used in the cockpit, aerospace PCB applications must be reliable, able to handle the stresses of atmospheric journeys while simultaneously making enough room for the rest of the surrounding equipment. Multilayer PCBs present an ideal solution in this case, with plenty of protective layers to keep heat and external stress from damaging the connections, as well as the ability to be made from flexible materials. Their higher quality and functionality also contributes to this utility in the aerospace industry, as aerospace companies prefer to use the best materials possible to keep their personnel and equipment safe.

And Many More! Multilayer PCBs are used in a wide variety of other industries, including the science and research industry and even home appliances and security. Everything from alarm systems and fiber optic sensors to atomic accelerators and weather analysis equipment uses multilayer PCBs, taking advantage of the space and weight savings offered by this PCB format, as well as their heightened functionality.

Why Are Multilayer PCBs So Widely Used?

The specific applications listed above represent only a fraction of multilayer PCBs applied throughout the industry. But why are they used so widely?

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 direction. 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 widely favored over value, 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.

With those irreversible trends and continuing progress of technology, many expect to see multilayer PCBs become even more abundant in the future.

How Are Multilayer PCBs Fabrication?

Packing the power of a double-layer PCB into a format that’s a fraction of the size, multilayer PCBs are becoming increasingly popular in electronics. They come in a wide range of sizes and thicknesses to accommodate the needs of their expanding applications, with variants ranging anywhere from four to twelve layers. Layers most often come in even numbers, since odd numbers of layers can cause issues in the circuit like warping, and are no more cost-effective to produce. Most applications require between four and eight layers. However, apps like mobile devices and smartphones tend to use around twelve layers, and some professional PCB manufacturers boast the ability to produce multilayer PCBs with nearly 100 layers. Multilayer PCBs with that many segments are rare to see, however, as they are incredibly cost-inefficient.

multilayer PCB stackup

4 Layers PCB Stackup

4 Layer PCB stack-up

4 Layer PCB  standard Stackup

4 LAYER 0.8 MM STANDARD BUILD

4 Layer PCB 0.8 MM Standard Build

4 Layer PCB 1.6 MM Standard Build

6 Layer PCB Stackup and Thickness

6 Layer PCB Circuit Board Stackup

8 Layer PCB Stackup and Thickness

8 LAYER 1.6 MM STANDARD STACKUP AND THICKNESS

8 Layer 1.6 MM Standard Stackup And Thickness

8 Layer PCB Stackup

A Typical 8 Layer PCB Stackup and Thickness

10 Layer PCB Stackup and Thickness

10 LAYER 1.6 MM STANDARD STACKUP AND THICKNESS

10 Layer 1.6mm PCB Standard Stackup and Thickness

Example 10 Layer PCB Stackup

12 Layer PCB Stackup and Thickness

12 Layer PCB Stackup

1.8mm 12 Layer PCB Stackup

12 layer PCB stackup thickness

Stackup Thickness of 12-layer PCB

Specialized Equipment for Pressing Multilayer PCB Circuit Boards

PCBs Manufacturing multilayer PCBs requires a specialized hydraulic press with heated platens. Initially, the books are squeezed with a “kiss” pressure of 50 psi before being heated to 350F at 350 psi for a minimum of one hour. The assembly is then allowed to cool slowly before removal for further processing. At Omni, the maximum size of a multilayer board is “12×16″ while the board thickness can range from 0.015″to 0.125”.

Multilayer PCBs Fabrication Process

The outer layers of multi-layer consist of sheets of glass cloth pre-impregnated with uncured epoxy resin (prepreg) and a thin copper foil.

The lay-up operator has already placed a copper foil and two sheets of prepreg on the heavy steel baseplate. Now he sets the pre-treated core carefully over the alignment pins. Then he adds two more layers of prepreg, another copper foil, and an aluminum press plate

He builds up to three panels on the baseplate in the same way. Then he rolls the massive stack under a press which lowers down the steel top plate. He pins the stack together and runs the finished stack out of the cleanroom into a rack.

The press operator collects three stacks on a loader and loads them into the bonding press. This press uses heated press plates and pressure to bond the layers of the PCB together. The heat melts and cures the epoxy resin in the prepreg while the pressure bonds the PCB together. The process is computer controlled to build up the heat and the pressure correctly, hold it, and then to cool the press down. In this way, we ensure a permanent bond that will last the lifetime of the PCB. Our board has four layers, but complex PCBs for defense, avionic, and telecommunications applications can have more than 50. These may include sub-assemblies of cores, prepregs, and foils drilled and plated before being assembled into the final PCB.

Once the cycle is completed, the press operator unloads the press and carefully rolls the massive stacks into the cleanroom. Here the lay-up operator de-pins the stack and removes the top plate. He unloads each of the panels from the stack, eliminating the aluminum press plates used to ensure a smooth copper finish. The copper foil is now bonded in place to form the outer layers of the PCB.

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Design for Manufacturability (DFM) for Multilayer Circuit Boards

PCB design plays a vital role in determining the mechanical, electrical, and thermal performance of the complete electronic system. Many advanced electronic components use multilayer PCB because it allows a large number of elements to incorporate on a single board, hence allowing the higher component density. Some PCBs are highly complex that make use of electronic components that are embedded in the substrate material.

Signal integrity and power integrity are two essential features you must take into consideration before you intend to make PCB layout design. You must adopt the following rules to maintain complete power integrity and signal integrity of the PCB.

Conductive PCB trances are composed of copper that comes with finite resistance. Voltage drop in many digital systems can severely influence the quality and accuracy of the system at that resistance when small current flows through the system. Controlled impedance trances are required to maintain the high efficiency of the system.

If significant current flows through the board, it exceeds the temperature beyond standard value because of the resistance of trances. To control board temperature and increase PCB reliability, the width of the trances must be increased, which, if not possible, due to the overall predefined circuitry. Copper thickness must be increased to 2 to 3 based on your needs and requirements.

Stray inductance can cause voltage spikes on the board, which can be handled by using the decoupling capacitors near the load.

The magnetic field is generated when current passes through the traces. This magnetic field can harm or influence the components that come under the range of the magnetic field. To avoid this process, elements must be placed with larger space between them, which is near to impossible in case of a compact multilayer design. So, an alternative way to overcome the effect of the magnetic field is to add a return path or ground plane. A ground plane will behave like a shield and helps in providing a return path of any signal. Ground planes generate decoupling in multilayer PCBs.

Analog and digital portions of the circuit must be separated from the ground planes, and they must be connected at a single point.

It is recommended to avoid 90-degree trances because of EMI issues.

Better to avoid long tracks for the traces containing both analog and digital signals. Noise coupling can be avoided if both signals cross at one point.

The Difference Between Single-layer PCB, Single-sided PCB, and Multi-layer PCB

Single Layer PCB vs multilayer PCB

When it comes to Printed Circuit Boards, an immediate question before the design is whether to use single or multi-layered PCBs for your circuit. The benefit and use of each depend entirely on what you intend to do. First, we should define each type of circuit board.

Single-layer or single-sided PCB

These PCBs simply have components on one side of the board and the conductor pattern on the other side. This reason is why it`s known as a single-sided or single layer PCB. Often, these are used for simpler devices as no wires can cross if the circuit is to function correctly. These are usually slightly cheaper to manufacture than multi-layer PCBs.

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