#5. Structure of the PCB

Choosing technologies sets requirements for how the PCB structure should be. The structure also depends on the complexity. It is all about how many layers you want to define and which type of via holes you have.

The PCB structure, similar to the choice of material, also has something to do with signals and impedance. You can easily have certain requirements for the specific impedance. Therefore, make thorough calculations on the impedance before embarking on the design.

As mentioned, the impedance can be connected to both construction and choice of material, because there can be losses in the isolation material – and if that loss is too significant, you cannot use it for very high frequencies. So, this is another factor where you can make the wrong choice. It could be very possible that you should have chosen to go with a different material. However, these materials are often more expensive.

Wise tip!

There is always a balance between the fact that the product should not be too expensive to develop, but there are still specific requirements to fulfil.

Calculations of impedance – a cross-section of a PCB with isolation material.

PCB types

Another factor you can use to define the structure, is the type of PCB. The most common types are:

• Rigid PCB
• Flex PCB
• Rigid-flex PCB

  Rigid PCB is the standard type, which has a thickness of approx. 1-2 mm. It is usually made from resin and glass fiber.

  A flex PCB, on the other hand, is soft in the material and can be folded in places where there are no components. The flex PCB is typically used in cameras and cell phones where space is limited.

  The rigid-flex PCB makes it possible to fold specific elements while others are rigid.

The choice of PCB type also depends on the purpose of the design. The flex PCB, for example, is the obvious choice for compact constellations. You will decide this in advance, based on what product you are making. If it will is going to be in a square or rectangular box, it is not all that important, but if it needs to fit in a compact piece of technology, you must be able to fold it.

Therefore, make sure to choose the PCB type that makes the most sense for the project, so that you can get the most out of the PCB structure.

Example of a flex PCB