A PCB stackup refers to the arrangement of copper and insulating layers that make up a PCB. These layers are arranged in a way to get multiple printed circuit boards on the same device. At their most basic, multilayer PCBs consist of at least three conductive layers. The bottom layer is synthesized with the insulation board, and each circuit board layer is connected to the next.

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1.       What is the basic definition of PCB stackup?

A stackup is the arrangement of layers of copper and insulators that make up a PCB before designing the final layout of the board. Managing a good stackup is not exactly easy and companies that make multilayer printed circuits such as Proto-Electronics, a European platform dedicated to the rapid prototyping of SMT printed circuits and cross-section components, for professionals, must be at the forefront.

Having multiple layers (see figure 1) increases the board's ability to distribute energy, reduces cross-interference, eliminates electromagnetic interference and supports high-speed signals. While a stackup level allows you to get multiple electronic circuits on a single board through the various layers of PCB board, the structure of the PCB stackup design provides many other advantages:

·  A stack of PCB layers can help minimize the circuit vulnerability to external noise, as well as minimize radiation and decrease impedance and crosstalk problems on high-speed systems;

·  Good PCB stacking can also contribute to efficient and low-cost final production;

·  A correct stack of PCB layers can improve the electromagnetic compatibility of the project.

With a single-layer or double-layer PCB the board thickness is rarely considered. However, with the advent of multilayer PCBs, the pile of materials is starting to become more and more critical and the final cost is the factor that affects the entire project. The simplest stackup can include 4-layer PCBs, up to the more complex ones that require professional sequential lamination. The higher the number of layers, the more the designer is free to unravel his circuit, with less chance of stumbling into "impossible" solutions. The PCB overlapping operations consist in the arrangement of the copper layers and the insulating layers that make up a circuit.

2.     What is the standard board thickness of PCB stackup?

The thickness of a PCB mainly depends on factors such as copper thickness, materials used, number of layers, and the operating environment. The standard thickness of a conventional board is around 62 mils (1.57mm). Today, PCBs have become more complex as the copper layer weight and the layer count have increased for various applications. Due to this, the PCBs tend to become thicker. Manufacturers, based on the customer’s request, are now fabricating PCBs with two new standard thicknesses, 93 mils (2.36mm) and 125 mils (3.17mm) (150% and 200% of old standard thickness).

3.     What are the advantages of PCB stackup?

Having multiple layers (see figure 1) increases the board's ability to distribute energy, reduces cross-interference, eliminates electromagnetic interference and supports high-speed signals. While a stackup level allows you to get multiple electronic circuits on a single board through the various layers of PCB board, the structure of the PCB stackup design provides many other advantages:

·  A stack of PCB layers can help minimize the circuit vulnerability to external noise, as well as minimize radiation and decrease impedance and crosstalk problems on high-speed systems;

·  Good PCB stacking can also contribute to efficient and low-cost final production;

·  A correct stack of PCB layers can improve the electromagnetic compatibility of the project.

4.     What are positives for PCB stackup organization?

As PCB technologies have improved and consumer demands for faster, more powerful products have increased, PCBs have changed from the basic two-layer boards to boards that have four, six, and as many as twelve-to-sixteen layers of dielectrics and conductors. Why increase the number of layers? Having more layers increases the capability of the board to distribute power, reduce cross-talk, eliminate electromagnetic interference, and support high-speed signals. The number of layers used for a PCB depends on the application, the operating frequencies, pin density, and the requirement for signal layers.

5.     What is the perspective of PCB stackup?

Regardless of the number of layers that comprise your board design, specifications for pad spacing, clearances, trace widths, copper weights and drill hole sizes must be tailored to your contract manufacturer (CM). If your design requires multiple layers, you will need to consider additional design for manufacturing (DFM) specifications for signal, power and ground routing through vias, as well as the PCB stackup. These additions entail incorporating verticality into your design perspective.

The PCB stackup design perspective that includes both vertical and horizontal considerations is a three-dimensional approach that significantly impacts board fabrication and PCB assembly. For fabrication, the number of layers, their arrangement or stackup and type of material must be determined. These choices require coordination between thicknesses restrictions; material parameters; such as dielectric constant, the coefficient of thermal expansion and electrical strength, signal type isolation and drill hole options. For PCB assembly, via routing options and their effect on the soldering process are of great importance. The capabilities of your CM limit the choices for the vertical aspect of your design.

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