PCB layer: 9 Tips to create the best Multilayer PCB

 

A multilayer PCB (printed circuit board) is made of more than three copper conductive layers.

It can be created by combining/stacking the single-sided PCBs and double-sided PCBs at the same time. It is extremely high density assemble. This circuit board integrates several layers into a single PCB. These layers are present in the middle of the material.

They are available in a wide range of sizes and thicknesses to meet the needs of their applications with different ranging from 4 to 12 layers. Layers should be in even numbers because odd numbers of layers cause warping and many more issues in the circuit. . These layers are separated by a dielectric (an insulating material). Most of the applications require between 4 to 8 layers.

Let’s jump into our vital subject, when we’re going to manufacture a multilayer PCB for the first time, there are a lot of points we ought to think about before we get started. In this article, we’re going to learn about 14 tips for creating the best multilayer PCB.

1-Software selection  

Multilayer PCB will have various circuits that will flow the energy currents all over the board to perform functions for technology it is inside of.

Energy means a great deal of heat! This can be very damaging if it is not handled properly in the manufacturing process.

The proper CAD software will help us to select the suitable way to layout our board. Multilayer printed circuit board’s overheating and electronic noise problems can be sorted out by using proper software design. It can tell us to add more components that will help to solve the specific problems. The component rearrangement and layering are only possible with good software.

While working on the rigid PCB we should look at three areas:

Negative plane layers: Negative image plane layers are regularly used to make power and ground planes on multilayer PCB formats/layouts. Some CAD devices require clearances incorporated into pad and footprint shapes for drilled holes in a negative plane layer. On the off chance that we are utilizing one of these PCB design software devices, ensure that our pad and footprint shapes are set up with the right negative plane clearances. On the off chance that our shapes are not set up for these clearances, we will make a short.

Pad shapes on inward signal layers: Some designs utilize diverse pad shapes on outside layers than on internal layers. For example, pin 1 pads frequently have a square shape for visual acknowledgment rather than the round shape that it ordinarily has on inward layers. If our libraries are not set up for multi-layer layers configurations, we may not get the ideal pad shapes on inward signal layers.

Drawing pieces: If we are making our fabrication and gathering drawings from inside our design layout, we presumably have various logos, tables, and Sand PCB views saved to our software. These should be altered for multilayer boards.

2-Fabrication shop requirements

The key is to work ahead with our fabrication shop so we comprehend their prerequisites for creating multilayer PCB designs before we start.

Fabrication shops will have various prerequisites dependent on the level of board technology that they can build to. A few shops may not be set up to build a multilayer PCB board over a specific layer check or with little trace and spacing widths. Moreover, they might be equipped for printing a double-sided PCB layout. If we exceed these limits, it might increase our fabrication expenses, or result in the board not having the option to be created on time.

Fabrication shops normally handle standard thru-hole vias, yet we should check with them first before using buried, blind or micro vias. What’s more, we ought to consult with them about trace width and spacing, and the amount and configuration of its layers. These components can affect their manufacturability, and we ought to have a reasonable comprehension of them before we start our rigid PCB layout design.

When our software is ready and we have checked ahead with the fabrication shop, now we can start creating our multilayer printed circuit board. Here are some tips for manufacturing a best multilayer printed circuit board:

3-Board size

Select the proper board size because it can cause constraints for determining the other features of our circuit. The size and number of constituents, the site where it will be set up and our contract designer’s place area, clearance, and drill holes are the factors that influence the accurate size of the board.

The size of our board can impact the circuit design. It can give us more circuit pathways than a single layer and double layer PCB. Proper board size will reduce the risk of overheating. Board overheating can make it catching fire and burning that will ruin our application.

4-Layer design

 Layers ought to be designed and based primarily on signal types. The number of layers can be determined by using the following equation:

                                       Board area

PIN density = ———————————

                          Total number of pins/ 14            

We ought to consider our impedance needs, especially when we use controlled/fixed impedance. It is very important for layer optimization.

 

5- Via choice     

Our choice, blind, buried, through-hole or via-in-pad, is extremely vital as it can influence the complexity of creation and consequently the quality of our multilayer PCB.

 

6- Material selection

We have a lot of material choices when we are creating a multilayer printed circuit board. Electrical stability ought to be in our minds while we are designing it.

The best material use for the creation of multilayer PCB is polytetrafluoroethylene (PTFE). This material is selected because of its low dielectric constant and low loss characteristics. It can easily handle the changing and varying temperature. It is a popular non-stick coating.

With improper heat distribution, we have to face a lot of problems.

Choosing the best material for our multilayer PCB creation ought to be done on a layer-by-layer premise. Although, signal layers and ground plane distribution inside the stack ought to be symmetric and support great signal.

 

7- Proper layer stacking

One of the most important points for creating the best multilayer board is how we stack our layers. There are a lot of options for stacking layers but these ought to be guided by creation, development, and functionality consideration.

The signal layers ought to be designed/route in opposite directions, horizontally or vertically because it reduces the cross-communication problems.

Routing signal layers in the same direction can cause over-heating (a lot of energy in one direction) and will ruin our board.

In the lamination process, we combine the layers and add a protective coating on the upper side of the board. If lamination is not done properly, it will cause board overheating.

The old PCB layer footprints are not suitable for a multilayer PCB design and we need to look at additional requirements. According to the previous CAD system used, we may need to add more layers and features to a footprint for multilayer use.

Online consultancy services are a real benefit for getting access to a more modern PCB layer design system. It provides us the easier, latest, and best PCB footprint data source to work with.

The planning of layer stack-up is the major difference between a double layer PCB and a multilayer board set-up. For creating our layer stack-up we should follow these points:

  • Efficiency: How quickly the hardware will work, and the working environment of the finishing board may affect the materials that it will be fabricated with. There are many advanced materials available in the market according to our desired application/product but it can increase our net cost.

Here is the place where the assistance of our PCB designer will be a critical source of information.

  • Net cost:The fabrication material, the number of layers, and configuration directly effect on the net cost for creating a multilayer circuit. Again, we need our designer’s assistance to think about all the options.
  • Density: The routing density of the board is another factor while deciding the configuration of board layer stack-up. It is critical because if we have not added accurate layers, we have to start layout design again or pay more for it.
  • Circuitry:We have to consider the need for our circuitry to create the best layer configuration.

Whenever we’ve assembled our information and created our board layer stack-up in the layout database, it will be the best time to begin placing and routing the board.

 

8-Place and Route the board

Multilayer board has similar components placing as with double-sided board. But both have different landscapes. Most of the routing occurs on the inner layers, so it needs more space for routing channels between the components.

We need to keep some points in our minds while working on internal trace routing and power planes:

  • We should have plans for routing spaces/widths and other needs like differential pairs or impedance controlled traces because it has more components and routing as compared to other PCB layer boards. 
  • A strip-line layer structure has needed for some routing and it should be close to ground planes. In cross perpendicular, sensitive routing internal signal layers prevent possible coupling.
  • Many vias are present in ground planes for connectivity but could influence signal return paths. For avoiding blocking up planes we should have strong planning.
  • Split planes should be laid out to avoid noise.
  • Close signal layers should be routed in the opposite directions on the multilayer board. Route one layer horizontal and the other two verticals in case we have close signal layers on layers two and three. This will be very helpful for avoiding a board-side cross-communication issue.
  • Check if the fabrication shop permits smaller inner layer pads for thru-hole parts and vias, and then decreases the size of inner signal layers. Later, it will facilitate more routing channels.

After placing components and routing, our next step is to build the best board.

9-Board manufacturing

Board manufacturing is vital for the successful application/technology and it is increasing day by day. The manufacturing process ought to be set up properly so that can handle the creation of a multilayer circuit.

 

For creating the multilayer circuit lamination process, stacking of the layers, drilling and etching of the board and testing processes are different and depend on our use.

This is designed by our “CM”. The selection of CM, drill hole sizes, trace parameters, solder masking choice, and DFM guidelines, our design, decision, and actions are greatly influence the procedure.

10-General tips

Accessible nodes: Sometimes, we need to figure out that why our multilayer PCB is not working and we want to estimate signal strength in our application. Before creating a multilayer circuit, we ought to consider all the points that will be critical for investigating our circuit but if they are not accessible, install test points to connect the signals. The incredible test points form a loop for test probes with hooks.

Proper spacing: We should have a proper plan for component spacing so that the wires can spread. More space is required if the component has more pins. Proper spacing makes soldering easy as well as facilitates auto-routing.

Proper components orientation: Proper component orientation with standard pin numbering, with pin #1 on the outer-left corner is vital. If the PCB layer components are equally oriented, we will not face any problem during soldering or component inspection.

Component size determination: Print out the layout design and match the components with layout paper. Sometimes datasheet can have errors.

Wiring direction: The wiring should be in the opposite (horizontal & vertical) direction between the layers. It will facilitate the wiring of lines that have to cross over the others.

Width of lines and current: Resistance can be reduced by larger width, later which will reduce the heat caused by dissipation. The width of the lines should be according to the current that will flow through them. All the current supplied by power lines so these should wider.

Layer thickness

The traces exceed in high temperature so, we should increase the thickness of copper layers for the multilayer PCB. The width of the traces should be increased to overcome the temperature.

11- Skilled Designer  

Multilayer PCB needs a professional and skilled designer. Without previous experience, this may cause problems. Multilayer PCB needs interconnection between several layers, but should simultaneously mitigate crosstalk and impedance problems. A single issue in the design may result in a non-functioning board.

12-Keep power and power plane separate

Use power and ground plane layers because these planes will distribute power and ground equally as well as make a micro-strip structure that can help signal integrity.

In the control circuit, the disruptive interference can be generated by large voltage and current spikes from the power circuit, which are usually low current and voltage.

We should keep power ground and control ground separate for each power supply stage. In case we want to tie them, do it at a point near the end of the supply path in this PCB.

13-Documentation and Output Files record

Most importantly, there will be more subtleties required on our manufacturing drawings. Our fabrication drawing will require a multilayer stack-up detail, and notes specifying the particulars of how it will be constructed. Second, if we are utilizing Gerber files for our manufacturing yields, we will have to make extra files for the various circuit layers. Here is the place where utilizing a high-level arrangement of CAD apparatuses can be exceptionally useful in making and dealing with our manufacturing yield files.

Luckily, there are PCB layer design frameworks accessible that as of now have the devices we need for the best multilayer circuit board design. Or then again CAD PCB manufacturer is the sort of cutting edge framework that will give us admittance to online CAD library administrations, board layout creation wizards, and manufacturing and documentation age utilities.

I hope these tips/guidelines will help us to create the best multilayer PCB.

Conclusion

Since we know about 13 tips for making multilayer PCBs, here is a portion of the reasons why we decide to make them will pay off:

To start, these PCBs are sturdy and adaptable. Because the material they are typically made of, PTFE, is considered a “soft” material. It is effectively controlled to find a way into various spaces. It is strong along these lines. It can assimilate the effect of a drop, which makes it doubtful to break.

Moreover, because PCBs are a few single-layer PCBs covered together, rigid/multilayer PCBs are incredible and compact. This has reformed the business, permitting technology to develop and turn out to be more versatile as the years go on.

This rigid PCB is top-notch. They are extraordinarily delivered and,  if we follow the tips above, we will see that a ton of exertion is taken to guarantee the boards are of the most ideal quality. This makes them ideal for technology like cell phones and workstations, which people desire to use for quite a long time before replacing.

Thus concluding, these 13 tips are sure to make the design/layout and manufacturing of our desired PCB a breeze. Follow these tips to create a high-quality multilayer PCB.

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