Multilayer PCB Design Guidelines
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Multilayer PCB is complex by design. The top and bottom layers look same as a double sided PCB but has staked layers on both sides of the core. All the layers are compressed to form a single Multilayer PCB where all the layers are interconnected via copper plated holes.
In this article, we will focus multilayer PCB design and provide you all the details about it. If you are interested in this topic, please check and read the content we provide for more information.
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What are the preparations for multilayer PCB design?
The first thing to look at when doing multilayer PCB designs is your CAD software. If you have only been designing single or double sided boards, your may not be set up for multilayer configurations. Here are three areas to look at:
Negative plane layers
Negative image plane layers are often used to create power and ground planes on multilayer PCB layouts. Some CAD tools require clearances built into pad and footprint shapes for drilled holes in a negative plane layer. If you are using one of these PCB design software tools, make sure that your pad and footprint shapes are set up with the correct negative plane clearances. If your shapes are not set up for these clearances, then you will create a short.
Pad shapes on inner signal layers
Some designs use different pad shapes on exterior layers than on inner layers. For instance, pin 1 pads often have a square shape for visual recognition instead of the round shape that it normally has on inner layers. If your libraries are not set up for multi-layer PCB configurations, you may not get the desired pad shapes on inner signal layers.
Drawing pieces
If you are creating your fabrication and assembly drawings from within your layout tools, you probably have different logos, tables, and PCB views saved to your software. These will have to be modified for multilayer boards.
What is the process of multilayer PCB design?
As a professional PCB designer, I have some tips for you that will help you in designing the multi-layer PCB efficiently.
· Always try to add an even number of PCB layers. Since both layers carry signals, the difference in the price segment for odd layers isn’t much. You will also rarely find a manufacturer who produces odd layers at much lower prices.
· Choose the right PCB thickness, keeping in mind the number of heavy components on the PCB board.
· For example, you can consider PCB with 0.8 thicknesses if all of the components are lightweight. The thickness support in multilayer PCB design varies with different vendors. However, some standard PCB thickness sizes are 0.8mm, 1mm, 1.2mm, 1.6mm.
· Select the PCB stack, as per the design requirements. The PCB engineer selects the method of ground and power planes totally based on the circuit design.
· Communicate effectively with the manufacturer and understand the capabilities of the PCB manufacturing.
· Cross-check Schematic connections with PCB design and footprints with schematic symbols.
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There are ample numbers of PCB manufacturers available in the market. One of the many factors which affect the cost of PCB manufacturing is the number of layers. Therefore, the cost of production for a multilayer PCB is higher than a single or double layer PCB. This cost increases, as we add more layers to the multi board PCB.
What are the considerations of multilayer PCB design?
1. Use software to determine layouts
Single-layer printed circuit boards are unique to multilayer boards. They don’t require layering or stacking. However, this aspect is obviously important in the creation of a functioning multilayer PCB. Why?
Multilayer PCBs will have a number of circuits that will send energy currents throughout the board to perform functions for the technology it is inside of. A lot of energy means a lot of heat! This can cause a variety of issues if not handled correctly in the design process.
Using design software can help you determine the best way to layout your board to avoid overheating and electronic noise issues related to multilayer PCBs. It can also suggest the addition of components that are there to help address these specific issues. The software can take the guesswork out of proper layering and component displacement, as well.
2. Choose the right board size
When considering how to create the best multilayer PCB, you will need to make sure you choose the right size board for your technology. The size of your board will impact the circuit design as well as the various components that you will need to use. In addition, one layer of your multilayer PCB will likely have fewer or more circuit pathways than another layer.
Choosing the right board size will also decrease the risk of overheating your board. Overheating boards could lead to the board catching fire and burning, which can render the technology the board is assisting virtually useless.
3. Choose the right material
As in the design of anything else, the materials you use will vary upon the way the product is used. In the case of multilayer PCBs, there are a number of options when it comes to the materials you can use in the production process. Especially because multilayer printed circuit boards must be carefully designed with electrical stability in mind.
One of the best materials used for the production of multilayer PCBs is polytetrafluoroethylene (PTFE). This material is chosen thanks to its low dielectric constant and low loss properties. This means that it can easily adapt to changing and varying temperatures. You likely have used PTFE before in the kitchen, as it is a popular non-stick coating for frying pans.
4. Optimize the manufacturing of boards
Manufacturing is increasingly important. Manufacturing issues can lead to problems that can render the technology useless. So, you have to make sure that your manufacturing process is set up properly to handle the creation of multilayer boards.
The stacking of the layers, lamination process, drilling, and etching of the board, and the testing processes will be different when creating multilayer boards. The fact that you’re making a multilayer board means that the sizes of your etchings, components, and drilled holes will all vary, but must be very specific for the ways you intend to use it.
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