Hello Friends! I hope you all are doing great, enjoying life and getting most out of it. We always feel happy when you keep coming back for what we have to offer. Today, I am going to uncover the details on the Introduction to Multilayer PCB. It is a type of PCB which comes with a combination of single sided PCB and double sided PCB. It features layers more than double sided PCB. I'll try to cover each and every aspect related to multilayer PCB so you don't need to go anywhere and find all information in one place. If you are new to PCB then you should first have a look at Introduction to PCB. In this tutorial, we are just gonna focus on Multilevel PCB but you should also read these Different Types of PCB. Let's hop on the board and discuss each and every feature of Multilayer PCB on by one.
- Before we jump in and explore what is multilayer PCB, we must have a knowledge what is PCB? It will give a better understanding and easy approach to get an idea about multilayer PCB.
- PCB is an acronym of printed circuit board which comes with different copper conductive paths, traces and lines that are incorporated on a single board to electrically connect different electronic components on the board.
- Multilayer PCB comes with a combination of one or two layer printed circuit board and features more complex design than Double Sided PCB.
- Number of layers on multilayer board are greater than number of layers on double sided printed circuit board.
- Multilayer board helps in increasing the available area for wiring.
- Multilayer board are developed by incorporating many double sided board together with insulating material between them.
- It must contains at least three conductive layers that are immersed at the center of the insulating material.
- Whenever we define number of layers, we refer to the number of conducting pattern on the board.
- Multilayer PCB is normally Rigid PCB because its too difficult to design it in Flexible PCB format.
- Depending on your needs and requirements, layers up to 100 can be incorporated on a single board to give it a multilayer pattern.
- However, 4 to 8 layer PCB is used for many applications because it provides the right amount of complexity required for most of the electronic projects.
- Some smartphones are equipped with 12 layer PCBs because they fulfill the requirement beautifully.
- Most of the time even number of layers are laminated on a single board because laminating odd number of layers makes the circuit design complex and leads to added amount of circuit issues during the execution of project.
- And it creates problems like twisting and wrapping once the soldering has been done.
- High cost is another issue in developing the odd number of layers on the board.
- Sometimes number of layers on multilayer PCB are laminated so closely that makes them very difficult for you to count total number of layers.
- However, if you give enough attention and look closely you can anticipate total number of layers laminated on a single board.
- The vias in the double sided PCBs have an ability to penetrate on the whole board. Vias waste space when you are available with number of conducting layers and you want to connect only some of them.
- In order to overcome this problem, Buried and Blind vias are used because they allow to penetrate those number of conducting layers that are necessary for the electronic project.
- In multiplayer PCBs, number of layers can be classified into different planes named as signal, power and ground places.
- Some PCBs come with more than one power or ground planes that are useful for the projects which require more than one supply voltage on a single board.
- If you are planning to design PCB online, then you should have a look at these Top Online PCB Design Services.
Construction of Multilayer PCB[dt_gap height="10" /]
- In order to produce multilayer PCB, number of layers of prepreg and core materials are joined together and are subjected to high temperature and pressure which remove any trapped air between the layers.
- Resin is used to cover the conductors around the corners, while adhesive material is properly melted to stick the different layers at one place.
- You can pick your material from number of different combinations ranging from exotic ceramic, epoxy glass, or Teflon materials.
- Figure above features the development of multilayer PCB where prepreg and core layers belong to same material. It is important to note that, prepreg used in this multiplayer PCB is not fully cured, which makes it more malleable and flexible than core material.
- The alternating layers of core and prepreg material are then put into the lamination press which comes with high temperature and pressure that helps in melting the prepreg and allows the layers to join together without leaving any space between them.
- Giving some time to cool off the material will result in a hard and solid multilayer board.
Rules to Design Multilayer PCB[dt_gap height="10" /]PCB design plays an important role in determining the mechanical,electrical and thermal performance of the complete electronic system. Many advanced electronic components use multilayer PCB, because it allows large number of components 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 on the substrate material.Signal integrity and power integrity are two important features you must take into consideration before you intend to make PCB layout design. You must adopt following rules in order 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 in order to maintain the high accuracy of the system.
- If significant current flows through the board, it exceeds the temperature beyond normal value because of the resistance of trances.In order 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, then 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 load.
- Magnetic field is generated when current passes through the traces. This magnetic field can harm or influence the compoents that come under the range of magnetic field. To avoid this process, components must placed with larger space between them which is near to impossible in case of multilayer compact design. So, alternative way to overcome the affect of magnetic filed is to add 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 generates 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.
Points to Consider to Identify Multilayer PCB[dt_gap height="10" /]If you have some PCB handy, and you feel skeptical for finding the total number of layers laminated on the board, you can do it by taking following suggestions, they will allow you to analyze total number of layers on the board.
- Expose the edge of the board on the shining light in order to see the copper planes. It will allow you to watch the signal trances more closely.
- Even if the multilayer PCB doesn't come with a blind via, we still can make use of bright light to analyze the inner layers.
- The best place to identify the inner layers is where there are no lines, paths visible on the outer layer.
- Some manufacturers imprint the label to identify the number of layers on the board. You can watch around the edges to identify the total number of layers.
Limitations of Multilayer PCB[dt_gap height="10" /]There are many benefits of picking multilayer PCB, but it also comes with some limitations and drawbacks that are essential to deal with before you make a final decision to choose multilayer PCB.
- High manufacturing cost is an important factor in selecting the multilayer PCB. You need to consider the overall project cost before you pick multilayer PCB.
- As compared to single layer or double layer PCB, multilayer PCB features more manufacturing time that is a major constraint while you are very much concerned for the time duration of the project.
- Multilayer PCB require more complex repair as compared to other PCB designs when they pertain to some permanent damage or certain loss.
Advantages of Multilayer PCB over single Layer and Double Layer PCB[dt_gap height="10" /]
- Multilayer PCB pertains to higher assembly density as compared to single layer or double layer PCB.
- EMI shielding is more easy and flexible when power and ground layers are placed carefully.
- There is no need of wiring interconnection which makes it an ideal choice for the projects which require low weight PCBs.
- It comes in smaller size that helps in reducing overall space required to connect the electronic components.
- Increased flexibility is another feature which puts it ahead from other PCBs.
Applications[dt_gap height="10" /]Multilayer PCBs are widely used in number of electronic applications and encompass intermediate to complex range of structures. Following are some applications where it is used for.
- Mobile Phones
- Heart Monitors
- Cell phone transmission
- Cell phone repeaters
- Atomic accelerators
- Central fire alarm systems
- Signal transmission
- Weather analysis
- Space probe equipment
- X Ray Equipment
- GPS Technology
- File servers
- Data storage
- Cat scan technology
- Fiber optic receptors