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A Critical Analysis of 7 Layer PCB and Its Applications

The demand for multilayer boards has continued to increase due to the complexity of electronic devices. Multilayer boards are widely used in several applications. Also, a 7 layer PCB is a good example of a multilayer board. Any board that comprises over two conductive layers is a multilayer board. Furthermore, the number of layers in a board depends on the application requirements. This article seeks to provide further information about 7 layer PCB.

What is 7 Layer PCB?

A 7 layer PCB is a more advanced type of multilayer board. This board comprises 7 copper layers. These layers include power planes, ground planes, and routing layers. A 7 layer PCB is ideal for high-speed applications since they include more routing layers.

Also, manufacturers use copper-plated holes to interconnect all the layers in this PCB. A 7 layer PCB is complex by design. The top and bottom layers appear as dual PCB. However, there are stacked layers on the two sides of the core. Manufacturers compress all the layers to create a 7 layer PCB.

In a 7 layer PCB, manufacturers assemble the active and passive components on top and bottom layers. The inner layers are for routing. Furthermore, a 7 layer PCB has a top layer, inner layers, and a bottom layer.  The thickness of a multilayer board increases as the number of layers increases.

The manufacturing process of 7 layer PCB requires precaution. This is because cross-connections and overlaps can occur.

What is a 7 Layer PCB Stackup?

7 layer pcb

The 7 layer PCB stackup is the arrangement of copper layers and insulators on a PCB. Before designing the final layout of a PCB, manufacturers must create a stackup. It is very important to manage a good 7 layer PCB stackup.  A multilayer board is specifically designed to offer solutions to certain problems.

A 7 layer stackup can help to reduce the PCB vulnerability to the external nose. Also, a good stackup can increase efficiency. Good layering can also minimize the board’s impedance and crosstalk. The 7 layer stackup configuration requires proper planning. A poorly designed stackup can increase EMI and crosstalk in a board.

Copper planes in a 7 layer stackup enable signals to route in microstrip or stripline. The function of planes in this stackup is to reduce radiated emissions. A 7 layer stackup comprises signal layers, power planes, and ground planes. In addition, it is important that the signal layer is adjacent to a plane. This helps to reduce the number of signal layers between planes.

Also, manufacturers should couple signal layers tightly to their adjacent planes. In a 7 layer PCB, a power plane can serve as a return path of the signal. Manufacturers add one more plane to the six layer stackup. This helps to improve EMC performance in a 7 layer stackup.

Furthermore, in a 7 layer PCB stackup, a prepreg layer functions as a dielectric between layers. Manufacturers apply pressure and heat to the whole stackup and melt the core and prepreg. This will help the layers to bond well. A 7 layer PCB features more copper layers and dielectrics.

Design Rules for a 7 Layer PCB

There are rules you need to follow when designing a 7 layer PCB. To achieve a functional board, it is very important you pay attention to some things. Here are a few design rules:

  • Route high-speed signals on intermediated layers. Ground planes can protect and tolerate the radiation coming from the tracks.
  • Ensure you place signal layers very close to each other.
  • It is better to use more ground plane boards since they enable signal routing
  • The mass and power planes must couple rigorously.
  • Ensure the insulation between a signal layer and adjacent plane is thinner.
  • Use multiple ground planes. They reduce the ground impedance of a board. Also, they minimize radiation.
  • Make use of efficient software to design stackup.
  • Consider the thickness of every signal layer.

Applications of a 7 Layer PCB

A 7 layer PCB is widely used in different applications. This multilayer PCB is well-suited for high-end applications.

Telecommunication electronics

You will find a 7 layer PCB in several telecommunication devices. They are available in radar electronics, satellite, GPS, and more. Also, most of these devices require high signal transmissions. A 7 layer PCB reduces crosstalk and EMI. Therefore, it is ideal for use in such devices.

Computer systems

A 7 layer PCB is available in computer systems. You will find them in graphic cards, motherboards, and other computer systems.

Consumer electronics

These are electronic devices commonly used in the household. Also, they are important for our daily lives. They include TV remote, smart watches, and more. Due to the complexity of some devices, manufacturers prefer to use this PCB.

Industrial electronics

Electronic devices in industrial systems feature 7 layer PCB. Industrial electronics are different from consumer electronics. Also, these electronics work in harsh environments. Industrial electronics like automated assembly lines and packaging conveyors feature 7 layer PCB.

The Fabrication Process of a 7 Layer PCB

A 7 layer PCB comprises signal layers, ground planes, and power planes. The signal layers are always used as the top and bottom layer.

  • Creating the inner layer core is the first step in the 7 layer PCB. This process starts by choosing a laminate that meets the required thickness of the board.
  • Choose the right materials for prepreg sheets, copper (Cu) foil, and inner layer core. The prepreg sheets comprise glass cloth reinforced with epoxy resin.
  • Cover the core sheet laminates with copper (Cu) foils. You need to bond the copper to the core material to create the inner layer laminate.
  • Cover the laminates with photosensitive dry films. This enables the UV light to have contact with the resist.
  • The internal layers are stacked with prepreg for alignment.
  • Cover the bottom and top prepreg layers with copper foil.
  • The next step involves heating the whole unit and fusing the layers in the circuit board.
  • Drill holes in the circuit board and apply copper on the drilled holes.
  • After this, add bottom and top circuitry. Cover and plate the circuitry with tin.
  • Etch away the extra copper and remove the tin. You can now apply a solder mask.
  • The last stage is testing the board for good performance.

Conclusion

A 7 layer PCB is ideal for use in some applications. This PCB adds to the performance of electronic devices. Also, they help to enhance signal transmission in high-frequency applications.