Multilayer PCBs

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Why Are Multilayer PCBs Preferred?

Discussion on electronics is incomplete without printed circuit boards (PCB). It’s very fundamental still holds a mask of mystery. The working mechanism behind the electronic device looks abstract as the circuitry is hidden. The flow of current cannot be seen end-user only experience its results. With the development of science and technology and the increasing density of integrated circuit packaging, leads to the high concentration of interconnect. However, in single-sided or double-sided circuit boards, the amount of crossover is limited and sometimes does not meet the design requirements at all. At the same time, in the case of a large number of interconnections and cross-requirements, the circuit board to achieve a satisfactory performance, avoid noise, stray capacitance, crosstalk, and other problems, it is necessary to expand the number of layers to more than two layers, thus the birth of the multilayer PCB board. Making multilayer PCB is a process in which two or more layers of electrical circuits are superimposed on each other, having a reliable predetermined connection to each other. The FR4 multilayer PCB, multilayer flex PCB, multilayer metal core PCB, Rigid-Flex PCB, multilayer ceramic PCB, high TG board and impedance board that we often refer to belong to multilayer PCB.

Multilayer Printed Circuit Board

In multilayer circuit board types, there are three or more alternating layers made of conductive material that are required that are buried in the center to manufacture PCB. The alternating layers are composed of core and pre-preg materials laminated with each other under extreme pressure and temperature to produce.

Resin encapsulates the conductors completely to make sure the complete absence of air between layers. The adhesive is melted and appropriately cured, which holds the conductive layers.

The combination of materials used has an extensive range, from pure epoxy glass to Teflon or exotic ceramic material. Core and prepreg are of the same material, but prepreg is more malleable compared to the core.

Then in the PCB manufacturing process is the lamination press, the alternating layers are placed where they experience very high temperature and pressure. Heat and pressure melt the prepreg and joins the layers firmly. After cooling-off, the materials, a reliable and hard multilayer board comes in the end.

Up to 100 layers can be combined on a single printed board according to the application needs required to create a multilayer pattern. Mostly, the even number of PCB layers are laminated on the single board because laminating the odd number of layers makes circuit designing complex. During project execution, more circuit issues arise due to complexity.

It creates twisting and wrapping problems after the soldering is done. Developing an odd number of PCB layers also brings a high-cost issue. Multilayer is sometimes laminated very closely that it becomes difficult to count them.

Multilayer PCB planes

In multilayer PCB, the layers are categorized into different planes known as ground, signal and power planes. In some multilayer PCBs, there is more than one ground or power planes. They are used in projects where two or more supply voltages are required on the single board.

ViasInMulti layer PCBs

Unlike single layer PCB design, double sided printed circuit board, the viascan penetrate into the whole board. Space gets wasted by vias when there are many conducting layers and requirement is only to connect a few of them. To overcome this issue, use Buried and Blind vias as they allow to penetrate conducting layers necessary for the electronic project.

Copper has finite resistance and is used to compose conductive PC traces. At that resistance, the accuracy and quality of the digital systems can be influenced severely due to voltage drop when current flows through the system. To maintain high system accuracy, controlled impedance trances are used.

There are numerous advantages that multilayer PCB provide in terms of design and technicality:

1.High Functionality and Capabilities:
The features and capabilities of multilayer PCB efficiently increase by laminating the layers together. The more circuitry and wiring can fit into the printed board by growing layers.

2.Flexible or Rigid:
Depending upon the application requirements, the multilayer PCB is either made flexible or rigid configurations. However, adding more layers to decrease the flexibility of the board.

3.Small Sizes:
With smaller footprints, brings high capacity by combining multiple layers in the stack also saves space, which is a plus point for manufacturing small devices.

4.Lightweight
The multiple layer configuration eliminates the connectors’ requirement of separate PCBs. The weight makes the manufacturing process simplex, saves space, and overall weight of the board reduces as well.

5.High Assembling Density:
Throughlayering, the density multiplies in multilayer PCB as compared to single-layer PCBs with limited frequency because of their surface mount area. The high density improves capacity, allows greater functionality and increased speed despite their small size.

6.Improved Design Functionality:
With the incorporation of excellent design quality, controlled impedance features, and provision of EMI shielding by carefully placing ground layers and power provides EMI shielding.

7.Increased Durability:
By nature, multilayer PCB is likely to be durable. Durability enables PCB not only to resist their weight but also handle the pressure and heat used to bind layers together.

Applications of Multilayer PCB

Multilayer PCBs are used extensively in various professional electronic devices because of their versatility and advanced technology. Applications, where multilayer PCBs are used widely include:

1.Computer Electronics:
From servers to motherboards,multilayer PCBs are used almost in everything. Their increased utilisation is due to the high-functionality and space-saving benefits.

2.Telecommunication:
Devices in telecom often take advantage of multilayer PCBs in numerous applications such as mobile phone, satellite technology and GPS applications, and signal transmission.

3.Industrial:
Multilayer PCBs are also popular in various industrial applications to run machinery. The most important industrial use is the controls.

4.Medical Equipment:
In the health industry, electronics are an essential part of diagnosis to treatment. The standard medical applications are medical testing devices such as CAT scan equipment, heart monitors, and modern X-ray devices where multilayer PCB technology is used.

5.Defense and Military:
High-speed circuits require high functionality, durability, lightweight, and multilayer PCBs have these features; thus, they are desirable in military applications. Due to the increased movement of defense industry towards the highly robust engineering designs, the need for multilayer PCBs is high due to their small size.

6.Automotive:
In the modern era, vehicles are more and more relying on electronic components, especially with the arrival of electric car technology. Headlight switches, engine sensors, GPS, or onboard computers, everything is controlled using electronic circuitry. The automotive manufacturers favor the features of multilayer PCBs as they are fit for the internal environment of the automobile.

7.Aerospace:
Like rockets and cars heavily rely on electronics, the aerospace industry is no way behind them. From ground computers to cockpit, multilayer PCBs are always in consideration for their design manufacturing.

The PCB manufacture process of multilayer category takes more planning, designing, and investment to produce efficient products. Thus when compared to the regular PCBs, multilayer circuit boards have better quality in terms of performance and functionality, but the cost can be high.

Why choose PCBONLINE multilayer PCB

PCBONLINE is a multilayer PCB manufacturer with 15 years of experience in China. With rich professional manufacturing experience in multilayer pcb technology and advantages in multilayer PCB price.

1.In the production of multilayer PCB, it is difficult for many multilayer PCB manufacturers to control the warping degree of boards, especially PCB with more than 10 layers. However, PCBONLINE has very good control in this aspect. Our project can be controlled by the following methods: A.The arrangement of the prepregs between each layer shall be symmetrical. For example, in six layers, the thickness and number of prepregs from the first to the second and from the fifth to the sixth layers shall be the same, otherwise, the lamination will be prone to warping.
B.Multilayer core plates and prepregs shall be made from the same supplier.
C.The line area of the outer layer side A and side B should be as close as possible. If side A is a large copper surface, and side B only have few lines, the printed circuit board is easy to warp after etching. If the line area difference between the two sides is very large, separate grids can be added on the sparse side to balance it out.

2.After the production of all the inner and outer layers, all the AOI tests will be carried out. For the impedance PCB, all the line widths will be within the tolerance of +/-10%. For the open-circuit boards, they will not be repaired and will be scrapped directly.

3.Multilayer PCB connects the inner and outer layers together through copper in the hole wall, so copper through holes is crucial for multilayer boards. In the production process, it is easy to have no copper in the hole. During the production of PCBONLINE, strict control is carried out by the following methods. A.Because the multilayer PCB is through many single and double boards stacked together and pressed together. During drilling, PCBONLINE reduces the cutting speed and rotation speed, and all the drill bits are completely new, which can reduce burr and roughness of the hole.
B.Before electroplating, PCBONLINE must have the process of removing rubber residue, to ensure that all burrs in the holes are removed clean, to prevent the electroplating without electricity to copper, resulting in no copper in the holes.

4.Surface finished is also critical to the quality of the multilayer PCB A.If the surface finished of the multilayer PCB is HASL lead-free, even if the customer does not require the use of high TG material, PCBONLINE use high TG board by default to prevent the bursting of the board when spraying tin.
B.The gold covering the surface of the pads in the ENIG surface finished process is flat and very easy to weld parts. It will not have poor soldering conditions resulting in pseudo soldering. Because there are many reasons that can cause pseudo soldering, in addition, engineers to deal with the problem of pseudo soldering is very troublesome, so multilayer printed circuit board ENIG process, generally can be very good to avoid pseudo soldering. PCBONLINE all suggest customers to adopt gold sinking process. Meanwhile, PCBONLINE has its own production line of immersion gold process, which can reduce the cost of multilayer PCB boards and reduce the procurement cost for customers.

5.Leading process capability in the industry.The following table shows the process capacity of PCBONLINE

Item Value
Layer count 8-24
HDI Stack up 1+N+1,2+N+2,3+N+3(with copper filling)
Final board thickness 0.15-3.2mm
Aspect Ratio Laser via
PTH
3:4
10:1
Copper thickness 1/3~6oz
Impedance
Control
Single Ended
Differential
+/- 10%
+/- 10%
Line/Space Inner Layer
External Layer
2.5/2.5mil
2.5/2.5mil
Min Drill Bit size 8mil
Hole size
tolerance
PTH
NPTH
+/-3mil
+/-2mil
Hole Position Tolerance +/-2mil
Profile
Tolerance
Puching
Routing
+/-3mil
+/-4mil
Soldermask Line to PAD
Registration
4mil
+/-2mil
Warpage 0.5%
Surface Finish HASL(LF HASL)
ENIG
OSP
Immersion Tin
Immersion Silver
Hard Gold Plating
Peelable Mask
Carbon ink
SMD 40-2000u", GND 30-800u"
Au 1-5u", Ni 80-200u"
 
0.8-1.2um
0.15-0.45um
Au 1-50u", Ni 80-200u"
5mil
0.3mil

The knowledge involved in multilayer pcb technology is enormous. If you can contact us directly on design, for example:

1.The impact of the thickness of the multilayer on the impedance. Our engineers carry out the multilayer PCB thickness through polar SI9000 software , and we can help you check whether the impedance line is reasonable or not.

2.multilayer pcb stack up structure, how to choose a more reasonable structure, so that the procurement cost is lower.You can also change the pressing structure directly in our ordering system