Multilayer PCB Manufacturing - Up To 30 Layers

What is a multilayer PCB?

The PCB with two or more copper conductor foil layers is a multilayer Printed Circuit Board. The multilayers in this PCB appear as double-sided circuit boards, laminated and glued together with the heat resistive insulation between them.

The whole construction is such that the top and bottom layer looks like the double-sided PCB. However, many stacked layers are compressed together to form a multilayer PCB. The top and the bottom layers have all the electronic components, and the inner layers help in routing.

The electric connection between the layers is through vias either by blind & buried vias or copper plated holes. The multilayer PCBs are available in different sizes and thicknesses, and the layers in a multilayer PCB can be up to 30 depending on the need of the applications.

Steps are used in the multilayer PCB manufacturing process

While manufacturing a multilayer PCB, you need to take particular precautions to avoid cross-connections, such as copper or overlaps. You need to do the whole manufacturing process in an ESD safe and cleanroom environment. Further, if you want to make an 8+ layer PCB, you need special equipment and setup.

Follow these steps in manufacturing a multilayer PCB.

Firstly, design a PCB layout with the help of any PCB design software or a CAD tool.
Secondly, design the inner layer core by treating the laminate of desired thickness with copper foil, UV light, and dry film resistance.
Thirdly you need to do lamination. You need to stack the inner layer core, prepreg sheets and copper foil sheets. While stacking, use holes to align the sheets of materials together. If you are making a four-layer circuit board, you need to stack layers in this sequence; bottom copper foil layer, prepreg sheets, inner layer core, prepreg sheets, and final copper foil on the top.
Now, apply pressure, vacuum and heat to ensure no air is left in between the layers. The process may take up to 2 hours, depending on the count of layers.
After treatment, resins from the prepreg sheets bind together the sheets, core and the foil to form a multilayer PCB.

Which Materials are used in Making Multilayer PCB?

The manufacturing of multilayer PCB mainly requires three raw materials, namely, a resin system, reinforcement materials and copper foil.

The resin system: Mainly, there are three types of the resin system used in the manufacturing of multilayer PCBs

Standard flame-resistant epoxy resin
Modified high temperature and high-performance epoxies
Polyimides

Reinforcement materials: You can use E (electrical) glass as the common reinforcement material for multilayer PCBs, and it works as a support vehicle for epoxy resins. This glass material has good resistance to water, fair alkali resistance and poor resistance to acid. Also, it has high dimensional stability.

Copper foil: The last material you need to manufacture a multilayer PCB is copper foil. You need copper foil during the electrodeposition process. Nowadays, PCBs need to be denser and thicker with more delicate circuits; copper foils should have elongation properties at high temperatures. It should also have unique bounding treatments for polyimides and epoxies.

FAQs about Multilayer PCB

1. What are the benefits of a multilayer PCB?

You can get several benefits from designing a multilayer PCB. These are:

Compact size: The final product is pretty compact after stacking multiple layers in a multilayer PCB. The technology that you enjoy in your handy smartphones and smart wristwatches is due to the compact size of these PCBs.

Better flexibility: multilayer PCBs are pretty flexible, and thus, they can withstand higher stress and vibration. Often, traditional PCBs fail at such high vibration and stress conditions. Further, you can route signals and power more efficiently through these PCBs and thus enjoy superior performance and reliability.

Less noisy: The radio frequency designs, including 433Mhz to 2.4Ghz high-frequency signals and high-speed signals, need a good grounding shield. In the case of a double layer PCB, components cannot give a good ground shield in most RF designs. However, multilayer PCBs allow you to place ground and power places separately, giving a good ground shield to RF components. As a result, there is less noise or even noise-free PCB boards.

High quality: as the multilayer PCBs use superior quality materials in manufacturing and production, they can also safely work in harsh environmental conditions.

Impedance control: you need to route the relative impedance of USB, SPI and other such communication protocols with that of the track. The separate ground plane in multilayer PCB helps in controlling the impedance.

Ease of design: if the layers in a PCB are fewer, space is limited for setting up the circuits. As a result, the creation of the PCB becomes more complex. However, in multilayer PCB, you can add more layers and thus ease the process of designing.

Lightweight build: multilayers PCBs have a small size, and with a small size, the weight of the PCB also decreases. This lightweight construction is essential for modern electronics, where mobility is necessary.

Higher durability: multilayer PCBs are highly durable and can withstand the heat and the pressure needed to bind the different layers together. Further, multiple layers bind together with protective materials and prepreg materials in this PCB.

Single connection point: Multilayer PCBs do not coordinate with other PCB components but work as a single component. As a result, a single connection point in these PCBs is advantageous for small gadgets and electronics.

2. What are the Disadvantages of Multilayer PCB?

Although multilayer PCBs have several benefits, it is still not suitable for all applications. Here are some drawbacks of multilayer PCBs.

High cost: Multilayer PCBs are costlier than single- and double-layer PCBs at every stage of the manufacturing process, right from design to manufacturing. As its manufacturing process is complex and accurate, it requires more time. Further, the labour work and the machines for lamination and epoxy resin materials are pretty expensive. Also, integrating different layers with blind and buried vias adds further cost.

Professional designing: As said above, multilayer PCBs have a complex design. You need to hire designers who have previous knowledge and experience in this field. Designers must also have good knowledge regarding layer stacking, ground shielding and impedance control. A minute problem can also lead to a non-functional PCB.

Limited availability: As discussed, multilayer PCB manufacturing requires enormous expenses, and some limited manufacturers have the funds to invest in machinery and labour for this PCB manufacturing. Thus, you have limited choice when selecting a multilayer PCB manufacturer.

Manufacturing time: Due to the complex design, every step of multilayer PCB manufacturing requires more time, leading to more labour costs. Sometimes, the gap between the order placed and delivery is considerable.

Test and debug: As the design of the PCBs becomes complex, the testing of the boards becomes more and more difficult. Unlike single- and double-layer PCBs, you cannot detect the faults within the layer.

3. What are the Uses of Multilayer PCB?

Multilayer PCBs are increasingly being used in various industries in many applications. The higher functionality and compact size make them ubiquitous in every type of technology. Here are some uses of multilayer PCBs in different sectors.

Consumer electronics: All consumer electronics like smartphones, microwaves, and air conditioners use multilayer PCBs. The higher functionality of these PCBs makes your appliances intelligent and multi-functional. From remotes to smartwatches, every device is becoming smarter with these PCBs.

Computer electronics: In computer electronics, servers, motherboards, and every other thing use multilayer PCBs to save space and increase functionality.

Telecommunication: Telecommunication devices use multilayer PCBs for signal transmission, satellite application and GPS. The durability and functionality of multilayer PCBs make them suitable for telecommunication applications.

Industrial: In industries, machines are roughly handled. As multilayer PCBs are durable, small in size and functional, you can use them for industrial control, other control systems, and other major industrial applications.

Medical devices: Multilayer PCBs are also finding increasing use in the healthcare industry, from treatment to diagnosis. Their small size, lightweight nature and improved functionality make them suitable for heart monitors, X-ray equipment, CAT scan devices and medical testing devices.

Military and defence: There is a vast need for high-speed circuits in military applications. The defence industry uses multilayer PCBs due to their higher durability and functionality. Further, their compact design makes it suitable to incorporate extensive functions in a small device which is very much required in the defence industry.

Automotive: The automotive industry is focusing on electric vehicles these days. As a result, GPS, headlight sensors and engine sensors all use electronics for their operation. Thus, automotive manufacturers started using multilayer PCBs in automotive designs. Further, these PCBs are heat resistant, durable and multi-functional, which is a good fit for internal automobile parts.

Aerospace: Like automobiles, rockets and jets also use electronic devices for their operation. All the computers in the cockpit or on the ground need different PCBs to work efficiently. Multilayer PCBs are a suitable choice for all types of environments in the aerospace industry, and the multiple protective layers protect them from heat and stress. Further, these PCBs’ high-quality materials and improved functionality ensure equipment and the personnel will be safe in their use.

Other applications: Other industries where multilayer PCBs are used are the science and research industry, home appliances and security systems.

4. How does a Single-layer compare to Multilayer PCB?

Single-layer and multilayer PCBs have many similarities and differences. These include:

The name suggests that a single layer PCB has only one layer while a multilayer PCB has multiple layers.
You can find single layer PCBs in simple electronics, while complex devices use multilayer PCBs.
You need few resources, less expertise and less time to manufacture a single layer PCB than a multilayer PCB.
You will find simple design and easy manufacturing techniques in single layer PCB production. Still, the performance and quality remain good. On the other hand, a multilayer PCB has a complex design and thus needs complex manufacturing techniques and expert technicians to manufacture it.
You can manufacture a single layer PCB in higher volumes, but that is not the case with multilayer PCBs.
Mass production reduces the price per board of single layer PCB, and thus these are less expensive than the multilayer PCB. You cannot manufacture vast quantities of multilayer PCBs.

5. What are the Multilayer PCB Designing Tips?

You can use the following tips to design a multilayer PCB

Always try to route adjacent single layers in the reverse direction as it helps to prevent broadside crosstalk issues.
Keep the dimensions of the inner signal layer minimal.
Keep the power and ground plane layers separate from distributing power and ground evenly.
Try to choose a simple material for circuit board construction.
Optimize your vias selection as it will decide the complexity and quality of your multilayer PCB.
Optimize the layout design to know the number of PCB layers that deliver the perfect signals you require.
Choose a suitable board size to work out various attributes of multilayer PCB.
Always try to keep the number of PCB layers even. As both layers carry signals, the use of odd number layers will not create a significant price difference.

6. How can you choose the proper multilayer PCB manufacturer?

When choosing your multilayer PCB manufacturer, you need to consider multiple factors. Some of them are mentioned here.

Make sure that your manufacturer is ready to review your design and give his input. He should also be able to point out mistakes and possible problems with the design.
The manufacturer must have all the required resources and skills to design and produce multilayer PCBs.
Ensure that the manufacturer is ready to deliver the products on time. Further, there can be some last-minute changes, and he must be comfortable doing them.
Ensure that the manufacturer can deliver the quantity you ordered without falling short of resources, machines and labour.
The manufacturer must follow all your requirements and industry standards strictly. Also, he must perform all the PCB tests while manufacturing to ensure the customer’s complete satisfaction.
Ensure that the manufacturer can maintain confidentiality and trust between both of you.

7. What are multilayer PCB design rules?

There are some parameters with semiconductor manufacturers that help in designing multilayer PCBs. These parameters verify the accuracy of a multilayer PCB and apply it to the semiconductor manufacturing process. These are some design rules in multilayer PCB design.

Define the PCB pile-up. With this, you can determine the number of layers required based on their characteristics.
Select suitable via types. Ensure that the vias apply to the current carrying capacity, and you must know how to attach them.
Decide a breakout strategy for the board that works as a routine strategy. The strategy must be layer-based.
Ensure a good PCB design by checking the integrity of the signal. For this, you need to consider characteristics and length as signals rise and fall a lot of times.
Consider the static and dynamic performance of the power distribution network to check the power integrity.
The inner copper layers must be unbroken at min of 10 mils from the board fringes; however, 20 mil is more popular.
Ensure that via is cleared through the inner layers.

8. How can you identify a multilayer PCB?

There are several ways of identifying a multilayer PCB-

First, you can inspect the holes and vias on the PCB layers. In single layer PCBs, one side has all the parts while the other side has pins. On the contrary, you need to punch holes in the multilayer PCB to connect components across different layers. These holes and vias are identification marks of multilayer PCB. However, inspecting vias for identifying multilayer PCB does not work in case of buried vias. Buried vias are only in the inner layers and are invisible on the surface.

Second, observe the edge of the PCB. If it is slightly thick, it is a multilayer PCB.

Third, observe the copper surface under the layer and it is thicker, it is a multilayer PCB.

Fourth, you can observe internal layers of a multilayer PCB with the help of intense light.

Last, if you observe trails and tracks, you will see that multilayer PCBs have spot return single paths.

9. What Advantage does Multilayer PCB have over Single- and Double-Layer PCBs?

Single-layer PCBs have a conductor on one side and elements on another side. Similarly, two-sided PCBs have one substrate layer; however, there are conductive layers on both sides of the substrate. On the other hand, multilayer PCBs have several layers and thus offer several advantages over single- and double-layer PCBs.

As multilayer PCBs are massive, they can have more components than these two.
Multilayer PCBs have a compact size compared to single and double-layered PCBs.
Multilayer PCBs are easy to handle.
In multilayer PCBs, there are more circuit components in a small space, and thus these PCBs offer high functionality than others.
You can use multiplayer PCB for complex and sophisticated projects as it is high quality.
Multilayer PCBs require less power than other PCBs.
Multilayer PCBs are more durable than others, and these PCBs have a single connection point.

10. Why do PCBs need multiple layers?

Different layers in multilayer serve many purposes.

They help the PCB perform at a greater level and be a part of complex equipment.
Multiple layers in a PCB enhance its performance.
Multiple layers in a PCB mean more circuits through wiring and thus make them suitable for robust applications.
Multiple PCB layers help trace route by jumping from one layer to another, and it helps in routing many complex circuits.
Multiple layers prevent short circuits as supply and ground have individual layers and are thus isolated.

11. Which Components are used in Constructing Multiple PCBs?

Many components combine to form multiple PCBs. These are:

Led: it allows one direction flow of the current.
Transistor: it amplifies the charge
Capacitor: it holds the electrical charge and releases it whenever the circuit requires
Inductor: it helps in stopping the current change
Diode: it helps the current to pass through one direction only.
Resistors help control the electric current when it passes through it.
Battery: battery provides voltage to the circuit boards.
The hydraulic press helps transform all metallic objects into metal sheets via pressure. It also helps in thinning glass powder.
Pre-preg: it helps in holding the cores together. It comprises fiberglass along with resin (an epoxy-based material).
Sensors detect changes in environmental conditions and generate an electric signal sent to other electronic components.
Switches and relays: a basic but essential component, a switch is a power button that ensures the flow of current in the circuit.
Crystal oscillators: These are like circuit clocks that help attain stable timing elements.

12. How can you make a 4-layer PCB?

A 4-layer PCB means there are four layers to route electrical signals: the top layer, bottom layer and two inner layers (1 and 2). You place components and routing in the top and bottom layers while inner layers 1 and 2 are used as core and power planes for signal routing.

Solder mask with exposed pads covers the outer layer and provides a spot for mounting SMD and through-hole components.

For stacking multiple layers in a PCB, you have to sandwich copper foil, pre-preg material and the core material under high temperature.

Along with high temperature, you also need high pressure to squeeze out air completely.

The high heat helps in melting and curing the thermosetting materials.

Finally, through-hole vias help in holding the multiple layers together.

13. How does a Multilayer PCB Work?

In a multilayer PCB, there are alternating layers of conductive core and epoxy infused insulated fibreglass sheet called pre-preg. These layers are laminated together under high pressure and high temperature, which melts the pre-preg and joins the layer together. Once joined, electrical connections are set up among different components using conductive pathways.

14. What are the Two Sides of a PCB Called?

The two sides of the PCB are the primary and secondary sides.

If using a through-hole board, the primary side fits with the inner side of the components.

On the other hand, the secondary side, also known as the bottom side, is used as a component soldering surface.

15. How many Layers can a Multilayer PCB have?

A multilayer PCB has two outer layers and several inner layers, and the inner layers are separate conductor patterns. Most multilayer PCBs have layers between 4 to 12. Further, the number is mostly even as odd-numbered layers lead to warping.

Lastly, the total layers in a multilayer PCB depends on the clients’ needs.

16. Why are multilayer PCBs widely used?

The rise in popularity of multilayer PCBs is due to the following reasons:

The design and the process of manufacturing multilayer PCBs are complex and highly technical. Further, you need skilled labour for its manufacturing. As a result, users get products that are useful to them and trustworthy too.
The small size of multilayer PCBs makes them flexible to use in a wide range of applications. Further, the modern technology used in its manufacturing enhances its performance.
Today, users want portable equipment, and as multilayer PCBs are lightweight, they are easy to insert into various smart devices.
The fabrication process and use of modern technology make PCBs of high quality.
The installation of multilayer PCB is relatively easy, and you need not outsource this service.
As multilayer PCBs have a protective layer, it does not get damaged easily and thus are more durable.
With multiple layers, you can put high-density components in a small space making these PCBs highly efficient.

17. What Factors Determine the Number of PCBs to be used?

There are several factors that decide the number of PCBs. These are:

Insulation resistance

Insulation resistance is the resistance of wires, cables and electric equipment insulation in Mega ohms. In the case of PCBs, insulation resistance guards against current discharge amongst conductive laminates.

Thickness

Structural stability requirements, and depending upon the number of components to be mounted on PCB, the number of PCB layers is decided.

Flame Resistance

Resistance to ignition is a prime property that governs the number of PCB layers. Flame resistance value shows the inherent capacity of PCBs’ resistance towards catching fire or igniting when the temperature rises.

Surface Resistivity

Humidity on PCB surface, surface contaminants and surface finish over PCB area affect the leakage current through the surface. Surface current discharge, due to low surface resistivity, cause current to flow between otherwise insulated electrodes on PCB surface area

Volume Resistivity

Volume resistance determines the flow of current through the volume or body of a PCB. Factors like moisture, chemical composition, & temperature affect it. The number of PCB layers depends on the allowable leakage current.

18. What are the Final Thickness Standards for Multilayer Builds?

The final thickness standards refer to the final density of a multilayer board. Generally, the standard final thickness of a multilayer PCB is 1.55mm. There can be three combinations of copper in the outer and inner layers; however, the final thickness depends on the circuit patterns. If you use solid copper planes, PCBs will have more thickness than PCBs with little or no copper. Further, the outer and inner copper layers have a thickness of 35 µm.

19. How can your Understanding of the Multilayer PCB Assembly Process help reduce the PCB Cost?

If you are well-versed with the PCB assembly process, you can lower the cost during its manufacturing. Some ways which help you cut the cost of PCB manufacturing are:

Pick the suitable material to create a PCB with less weight. Also, pick material that shows performance regarding tensile strength, temperature, dielectric constant and flexibility.
Please don’t go for the complex board shape as it demands high precision and accuracy, leading to additional cost overheads.
Keep the size of the board small enough to accommodate all components. Extra board size will also increase the cost of production.
Check the connection of holes and vias the inner layers to ensure good circuitry. This will reduce the price incurred in repairs.
Use antipodes to ensure clearance of via through inner layers.
You must do the electrical testing of the multilayer PCBs while manufacturing to avoid any short circuits. This test will help in cutting the costs involved in frequent repairs.
Ensure that whatever specifications you give to the manufacturer are essential. Unnecessary specifications can lead to a higher cost of manufacturing.
Decide the number of layers required in the PCB. Extra and unnecessary layers can increase the cost of manufacturing.

20. What are the Causes of Bow and Twist in Multilayer PCBs?

The bow and the twist are the two parameters that help you determine a PCB’s flatness. The bow is a cylindrical or spherical curvature of the board when all its four corners are in the same plane, while in a twist, deformation is parallel to the board’s diagonal. It means one corner is different from the other three corners.

There are several reasons for bow and twist conditions in a printed circuit board. Some of these are:

Bow and twists arise if you have chosen a material that is not suitable for lead-free soldering.
Another reason is not using pressing parameters for different layers that increase pressure in the final PCB.
At times, incorrect arrangement of the materials can also lead to bow and twist conditions.
It can arise if you have not used a heavy thermal shocker for cooling down the panels on a horizontal surface.
Not using a suitable soldering profile can also lead to bow and twist.
The soldering process needs adequate preparation and teamwork. If you do not get needed support, the results may have a bow and twist.
Asymmetric design with unbalanced stress conditions or variable thickness of layers may also cause bow and twist.
Not using horizontal ovens for the curing process as needed can result in bow and twist.

21. What are the Multilayer PCB Thickness Parameters?

PCB thickness affects its conductivity, resistance and its overall functionality. Several parameters that decide the overall thickness of PCB include:

Standard PCB thickness:

The standard PCB thickness is 0.063 inches or 1.57mm. However, you can choose from 0.008 inches to 0.240 inches on some boards. You can choose any depending on your application, insulating layer, and material content. You have to communicate your requirements to the manufacturer.

PCB copper thickness:

Copper is the main element that decides the functionality of the PCB, and its thickness plays a significant role in PCB standards. It is measured in ounces or oz. Generally, manufacturers produce PCBs with I oz of copper, and thickness is around 1.37 mils which is achieved by spreading the copper evenly over square feet. However, manufacturers can add the weight and width of the copper layer depending on the current requirements.

PCB trace thickness:

Trace thickness is also an essential parameter in PCB designing. The thickness of the copper traces can handle the increase in temperature from the operating temperature to the maximum operating temperature. A PCB designer decides the trace thickness. The appropriate trace thickness helps prevent PCB from overheating when the current flow increases.

Fr-4 thickness:

Fr-4 is the primary base material that is used in the manufacturing of PCB boards. It is a fibreglass structure that is transformed into a thin sheet. It gets its rigidity with the lamination of fire-resistant epoxy resins.

PCB thickness tolerance:

Thickness tolerance refers to the allowance of the substances used in PCBs manufacturing, and it is either less or more than the standard quantity of material.

22. What Machine is used in Pressing Multilayer PCB?

Multilayer PCBs need a particular press machine that presses PCBs’ different layers together. The Machine applies pressure on the PCB layers. Depending on its size, it is a firm Machine that either stands on the floor or the benchtop. It comprises an aluminium rack that holds its all components together. Its different components include a press plate, pressure supply and a heater. You can access its pressure parts with the help of a big door on this Machine.

You can create a multilayer PCB prototype with this press machine that matches the industry standards. The press compartment lift decides the number of layers in a multilayer PCB.

The press machine presses the different layers of PCB in the following steps:

Firstly, pin the board and fit the stack into the press plates.
Set and generate the pressure in accordance with the type of board used.
Turn on the heater so that the heating process starts
Pressing starts at a predefined temperature
Cooldown the Machine under controlled pressure
Take out your multilayer PCB from the Machine

23. What are the Key Preparation Stages in Multilayer PCB Construction?

Before you start the manufacturing process of multilayer PCB, you must review certain features to detect any faults in the design layout. With these preparation steps, you can save time correcting any flaws in the final product.

Some things that you need to consider before implementing your PCB design are:

PCBs have complex schematic diagrams and designs with several board layers. In this situation, circuit routes may not be appropriately defined. Thus, before sending your designs, check for any incomplete routes.
Check the consistency of board layout: the elements and the signals of the boards must match each other.
Check if designs are not broken: don’t ignore any design rules. There should be correct positioning and number of drill holes, spacing, trace widths, and spacing, vias.
Assess your Gerber files: don’t forget to check your Gerber files for any errors. View your Gerber files in the Gerber file viewer and check for aligned layers and other variations.
Once you assess all these components of your layout design, you can send it to the manufacturer for further processing.

24. What are the Complications Associated with Manufacturing Multilayer PCB?

PCB Manufacturers may face several challenges while manufacturing multilayer PCBs. Some of them are:

Mechanical distortions: Bow and twist are common during PCB fabrication. These errors change the board’s flatness, leading to assembly issues like solder paste deposition or component mounting. The right parameters when pressing multilayer PCB boards can help prevent these distortions. Additionally, using a similar substrate will enhance the uniform layer fusion. If a manufacturer uses appropriate machinery and standard guidelines, these issues are mitigated.

Thermal and electrical issues– The inappropriate selection of substrate material can lead to several electrical problems. The substrate materials are responsible for conduction and insulation between copper layers. Versatile substrates like Fr-4 can reduce major electrical issues in multilayer PCB manufacturing.

Delamination: The higher number of layers in multilayer PCBs increases delamination in various areas. Copper laminates can detach themselves from the surface layers, or the inner layers in their foil do not have good peel strength. Sometimes, delamination is hard to fix and can lead to re-spin.

Moisture penetration: Moisture ingression in the PCB can affect its functionality. Picking a substrate with low hygroscopic nature can minimize this issue. Further moisture penetration can lead to signal shorts and degrade the PCB performance.

Drilling issues: Drilling the layers in PCB is a critical step in manufacturing. The bottom layer has larger holes as compared to the inner layers. Some of the problems faced with the drilling technique are loss of circulation, hole cleaning and stuck pipe. Sometimes, back drilling minimizes the parasitic elements that come by plating through holes.

Selection of vias: Selection of via can also pose severe challenges in the PCB manufacturing process. For drilling blind and buried via, high precision is required.

Heat dissipation: Heat transfer from hot to cold components occurs through convection, conduction and radiation in PCBs. As multilayer PCBs have a very complex and dense design, mounting the heat dissipation components is challenging. Use of effective components with pre-planned thermal design.

Contamination: contaminants like dust, oil, fingerprints, moisture and layer of oxidation, can create complications in PCB manufacturing. Manufacturers must keep their laboratories clean; otherwise, fixing faults will result in higher costs and increased lead time.

Pressing issues: Pressing of layers together to form a single board in multilayer PCBs. Pressing can be challenging if the right materials are not used. Using the best laminate materials and high-quality press machines is always good.

25. What are the Three steps to Multilayer Printed Circuit Board?

Different layers are laminated together in a multilayer PCB to form a PCB. The outer layers are single-sided PCBs, while the inner layers are double-sided PCBs. There are pre-preg or insulating layers in between the conductor layers. There are three steps in preparing a multilayer PCB board. These are:

Structuring: In this step, manufacturers use the layout data to structure the traces on the base material. It is done with the help of lasers, cameras and automatic tools that helps in drawing the conductive paths precisely and quickly. The structuring process takes place layer by layer until all layers are stacked.

Lamination: After precisely stacking the layers, prepregs insulate the conductive traces on different layers. During lamination, prepreg mainly connects all the other layers. A multilayer press machine helps in pressing different layers to form a single board.

Through-hole plating: In this step, electrical connections are set between individual layers through the through-hole. Through holes means a hole from top to bottom of the multilayer PCB. Through holes are either plates or non-plated. Through-hole plating requires a special conductive paste, and it is a chemical-free process. For multilayer PCBs with more than four layers, through-hole electroplating is required.

26. What Software is used in Designing Multilayer PCB?

PCB designers use various types of Software to design a PCB layout, and they can use already available PCB designs in PCB libraries for developing PCB prototypes. Some software is paid for, while others are also available for free, and they can be easily downloaded and installed on a computer.

Some of the Software that a designer can use to design a multilayer PCB are:

Altium designer:

Helps in designing high-end PCBs
Has routing features
Easily available
Options for both schematics and layout

OrCAD:

Professionals use this tool as it has various PCB design tools.
It has features like 3D modelling, DFM checking, curved routing, auto-routing, group routing, etc.

PADS:

It is a cheaper option in PCB design software.
Free to download
It has user-friendly interface
Not suitable for beginners

KiCAD:

Free to use
Open-source Software
Online libraries available

Pulsonix:

Have all high-end features
Available in different versions
Support schematics for complex PCB designs

27. What is Multilayer Ceramic PCB?

Ceramic multilayer PCBs are those PCBs that use ceramic plates instead of conventional boards. As ceramic plates have high thermal conductivity and low CTE (coefficient of expansion), they are suitable substrates for PCBs. The different ceramic substrates are aluminium oxide, tantalum oxide and aluminium nitrides.

28. What is Multilayer PCB Stack-up?

Multilayer PCB stack up refers to the arrangement of different conductive and insulating layers in a PCB before the board layout design. With a PCB stack-up, designers can understand the complete circuitry of the PCB.

There are certain advantages of PCB stack-up design. These are:

It helps to minimize the circuit’s susceptibility to noise, radiation, and impedance.
PCB stack-up enhances the electromagnetic compatibility of your PCB design.
Depending on the cost of the PCB structure, you can reduce the cost of production.

Manufacturers need to know a few things before choosing a multilayer PCB stack.

Firstly, knowing the number of layers for determining power signal and ground layers.
Secondly, the layer arrangement should be known, i.e., positioning of different layers, stack up symmetry and spacing between ground and power layers.
Thirdly, determine the PCB materials to understand the electrical, mechanical, and thermal properties.
Lastly, determine the copper weight, routing and vias and type of vias used.

29. What is a Multilayer Flexible PCB?

Multilayer flexible PCBs have designs that precisely suit the products. In the construction of multiplayer flexible PCBs, the primary materials used are:

Substrate- it is either adhesive or adhesive-free substrates
Cover film- it has three parts, namely, release paper, adhesive, and PI
Reinforcing materials- it supports the strength imparting flexible characteristics to the PCB
Other auxiliary materials include adhesive, electromagnetic materials, and pure copper film.

Multilayer PCBs are becoming a popular choice among engineers due to several advantages:

Higher performance and reliability
Lesser weight and compact size
Higher signal frequency and bandwidth
Better power efficiency
Improve environmental compliance

Along with the advantages, there are also some disadvantages of these PCBs. These include:

As designed for special applications, the cost of designing and manufacturing is high.
If mishandled, these PCBs can damage easily
Once damaged, it isn’t easy to repair these PCBs.
It is difficult to change the dimensions of the flexible PCB as it depends on the size of the production equipment.

30. How much does a Multilayer PCB Cost?

In designing a multilayer PCB, there is a need for high precision, intricacy and accuracy. Thus, the end cost depends on the design and the end-use of the PCB. In other words, if you need a PCB for general use, it will cost you much less than a PCB for high-tech applications. Other than the manufacturing costs, you must also consider the shipping costs to decide on the final price tag of the products.

However, all these are just broad view assessments of the price. The actual cost of the PCB depends on several factors:

The choice of materials used in the manufacturing of the PCB
Size of the multilayer PCB
Number of layers in the PCB
Type of the finish used in the product
Spacing and minimum trace width
The thickness of the PCB and aspect ratio
The number of units you want
Delivery costs of the final products

31. What is Automatic Inspection for Multilayer PCBs, and How is it Done?

It is essential to perform tests to verify if all PCBs are working as desired. There are several advanced techniques of testing that include manual and automated tests. However, there are some factors that you must consider before going for PCB testing:

You must consider the inspection cost, which depends on the type of test technology.
The type of defect a PCB has. Every test technique detects different defects.
The inspection speed also matters as some methods are faster than others.

Manual visual inspection:

In this, technicians look at the PCB either with a naked eye or through magnification to check board thickness and assembly dimensions, look for any scratches, pits, or dents, and check if vias are correct.

Automated optical inspection (AOI)

In the automated optical inspection, technicians use a PCB inspection machine with several lights and one or more still cameras. The cameras capture the images, and the technicians compare those images with the original information on the board. There are 2D and 3D AOI equipment available. AOI is a prevalent and accurate technology that detects various faults which get missed by the naked eye.

Automatic Laser Test treatment (ALT)

ALT is another method of PCB inspection. It helps measure the dimensions of the solder joints, the reflectivity of different components and solder joint deposition. The ALT technology uses a laser to take measurements of the PCB assemblies. The light reflects, and the intensity and position of light help determine the component’s reflectivity. The ALT method also helps determine viscosity, alignment, cleanliness and other features of solder paste printing.

X-ray inspection:

X-ray inspection is also an ideal method of detecting defects. This X-ray equipment quickly identifies defects as rays can pass through board layers. Based on the rate of light absorption, it differentiates among different materials. It creates an image with the reflected rays and detects any faults in the solder connections accordingly.

32. What is Oxide Used for in the Process of Manufacturing Multilayer PCBs?

The manufacturing of multilayer PCBs needs oxide for chemical treatment on the surface of the inner layers just before lamination. It helps in improving adhesion during lamination. This oxidation process increases the roughness of the copper so that there is no fracturing and separation of the laminated years and enhances the laminate bond strength after manufacturing. Depending on the process, the oxide is either black oxide or brown oxide.

33. What is DIY multilayer PCB?

A DIY multilayer PCB is a PCB that you can manufacture at home. You can take local materials rather than expensive and complex materials from the laboratories for this DIY project. For DIY multilayer PCBs, you can also take the help of the software to design a layout. However, these PCBs’ durability, functionality, and accuracy are not up to the laboratory-made PCBs.

For manufacturing a DIY multilayer PCB, you will need:

A copper-clad board with a fibre sheet base
Glossy photo paper
Acetone,
Rubber alcohol
Knife
Scratch pen
Masking ink or epoxy
Solid ink printer
Laptop/PC
Hand drill

Steps to make a DIY multilayer PCB:

Collect all tools and place them in order
Separate fibre sheets from the copper clad board
Slice and clean the copper-clad
Transfer circuits to clad using heating elements
Etching
Aligning and securing copper clads
Apply mask ink and drill vias

34. What is multilayer PCB etching?

After performing the plating process, a dry film is on the board. Now, it is essential to remove the copper beneath the film. For this, the PCB goes through the etching process.

You have to remove the extra layer of copper, i.e., the uncovered area of the copper by tin. Removing the extra layer will reveal the traces and pads around the holes. Now, you will see the copper patterns.

Once done, you will remove the tin that covers holes and pads with the help of a chemical solution. After completing this process, you will only see the laminate and the copper of the circuit board. After the etching process, the basic skeleton of the PCB is complete.

35. How many ways can a Multilayer PCB be Soldered?

You can use PCB soldering through-hole PCB assemblies or surface mount assemblies. In the soldering process, a solder wire heats and melts with the help of a soldering iron. After this, it flows into the metal to be welded with a flux, and it forms a solid solder joint which is then cooled.

There are three different ways of PCB soldering:

Soft soldering: It creates a connection between different components over circuit boards. In this method, solder is a combination of tin with other metals, and the soldering iron is gas or electric. An acidic substance called flux ensures tight and efficient bonding, and a soft soldering bond is weaker than other soldering techniques.

Hard soldering: As the name suggests, it creates a strong bond by melting the solder at very high temperatures. The soldering material is silver or brass, and a blowtorch is used for melting. Here, silver is the base material, and thus, the process is sometimes referred to as silver soldering.

Brazing: it creates a much stronger bond than soft and hard soldering. It works on the hard soldering method of melting solder material at high temperatures. However, once the base material is melted, soldering material works as brazing filler metal once placed on it. The molten filler joins the base materials through capillary action.

36. Are multilayer PCBs high-frequency PCBs?

Yes, multilayer PCBs are also a type of high-frequency PCB.

Multilayer PCBs have multiple layers that give them high impedance control and thermal coefficient, and Multilayer PCBs have a ground plane essential for high-frequency applications.

37. What are the quality standards of multilayer PCB?

Specific quality standards guide different manufacturing companies to develop and manufacture printed circuit boards. These standards ensure to establish that they are safe and provide customers satisfaction.

Some of the quality standards are:

ISO 9001 ensures that a manufacturing company must meet customers’ requirements as much as possible within the regulated requirements related to a product or a service.
ATF 16949 standard guides manufacturers to assure security and quality in automotive products. These standards ensure the improvement of the performance and reliability of automotive components.
UL listing service requires manufacturers to test products thoroughly to meet all specific requirements.

38. How can you test multilayer PCB?

Several PCB assembly testing methods are an essential part of the manufacturing process.

In-circuit testing: this test powers up and actuates every circuitry to check the integrity of solder connections. You can perform this test on big connections and ball grid arrays.
Flying probe testing: this is a cheaper method that tests for Open circuit, short circuit, resistance, capacitance, inductance and any diode issues.
X-ray inspection: locate local defects like solder connection faults, barrels, or internal traces.
Automated optical testing: as explained earlier, it helps detect issues earlier in production.
Burn-in testing: It helps in detecting early failures and establishes load capacity.
Functional testing: this test verifies that the product will power up.

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