What is a PCB Stack-up? What should be Paid Attention to in Stack-up Design?

Today, the increasingly compact trend of electronic products requires the three-dimensional design of multi-layer printed circuit boards.

However, layer stack-up put forward new issues related to this design perspective.

One of the questions is to obtain high-quality laminated buildings for the project.

As the production of complex printed circuits consisting of multi-layer complicated printed circuits is particularly important.

Good PCB laminate design is critical to reducing the radiation of the PCB circuit and related circuits.

Instead, poor accumulation may significantly increase radiation, which is harmful from a safety perspective.

What is a PCB Stack-up?

The PCB stack-up is placed the insulator and copper layers of the PCB before the final layout design was completed.

Developing effective stacks are a complex process.

PCB is connected to the power and signals between physical devices, while the correct layers of the board material directly affect their functions.

Why do You Want a PCB Stack-up?

Developing a PCB stack-up is critical to designing high-efficiency circuit boards.

The PCB stack-up has many benefits because the multilayer structure can increase energy allocation capabilities, prevent electromagnetic interference, limit cross-interference, and support high-speed signal transmission.

Although the primary purpose of the stack-up is to place multiple electronic circuits on a plate through a multi-layer, the structure of the PCB stack-up also provides other important advantages.

These measures include minimizing the vulnerability of the circuit board to external noise and reducing the crosstalk and impedance problems of high-speed systems.

A good PCB stack-up can also help ensure lower final production costs.

By maximizing efficiency and improving electromagnetic compatibility of the entire project, the PCB laminates can save time and funds.

PCB Stack-up Design Considerations and Rules

  • Number of layers

Simple stack-up may include four-layer PCB, while more complex PCBs require professional sequential lamination.

Although more complex, higher layers allow designers to have more arrangements without increasing the risk of impossible solutions.

Typically, one 8layer or more layer is required to achieve the best layer arrangement and interval to maximize the function.

Use the ground plane and the power plane on the multilayer to reduce radiation.

  • Layer arrangement

The arrangement of the copper layer and the insulating layer constituting the circuit constitutes a PCB overlapping operation.

Preventing the PCB warpage needs to be arranged and balance the cross-section of the board. For example, in the 8layer PCB, the second layer and the seventh layer thickness should be similar to the best balance.

The signal layer should always be adjacent to the ground plane, while the power supply plane and the quality plane are strictly coupled together.

It is best to use multiple ground layers because they can usually reduce radiation and reduce ground impedance.

  • Layer material type

The heat, mechanical and electrical characteristics of each substrate and how they interact to select the PCB laminate material selection.

The board is typically composed of a solid glass fiber substrate core that provides the thickness and rigidity of the PCB.

Some flexible PCBs may be made of flexible high-temperature plastics.

The surface layer is a thin foil made of copper foil attached to the layer.

Both sides of the double-sided PCB have copper, and the thickness of copper varies depending on the number of layers of the PCB stack-up.

A layer of solder mask is covered at the top of the copper foil to contact the copper traces with other metals.

This material is critical to helping users avoid the correct position of the welding jumper.

A silkscreen printing layer is applied to the solder resist layer to add symbols, numbers, and letters to facilitate assembly, and make people better understand the circuit board.

  • Determine to wire and through holes

The designer should wire high-speed signals on the middle layer between the layers.

This allows the ground plane to provide shielded radiation that is transmitted from the rails.

Placement of signal levels close to the plane level allows the return current to flow on adjacent planes, thereby minimizing the return path inductance. There is no sufficient capacitance between adjacent power supplies and ground layers, and a standard construction technique is not available for 500 MHz or less decoupling.

  • Spacing between layers

Since the capacitance is reduced, the tight coupling between the signal and the current return plane is essential. The power and ground layers should also be closely coupled together.

The signal layer should always be close to each other even in the adjacent plane. The tight coupling and interval between layers are critical to uninterrupted signals and overall functions.

Conclusion: 

There are many different multi-layer PCB board designs in PCB stack-up technology.

When involving multiple layers, a three-dimensional method of considering internal structures and surface layout must be considering.

With the high run speed of modern circuitry, careful PCB stack-up design must be made to improve allocation capabilities and limit interference. PCB in design may reduce signal transmission, productivity, power transmission, and long-term reliability.

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