Design Considerations for PCB Stackups

A stackup is an arrangement of PCB layers of conductors and dielectric materials, which enables the incorporation of multiple boards compactly within a device. This mostly includes the substrate, such as polyimide by upper and lower layers of copper, followed by adhesive and cover layers on both sides. Multilayer stackups are becoming increasingly common because of the complexities in design and the rising number of small form factor devices. While single-layered boards are still made, considering the functionalities and compactness of modern devices, multilayered boards are preferred as they enable better EMI mitigation, energy distribution, and support high-speed transmission of signals. To enable these functionalities and support high-frequency applications, a PCB stackup needs to be designed carefully. This post discusses the factors to consider when designing PCB stackups.
 
Factors to Consider When Designing PCB Stackups


With a proper design strategy in place, designers can easily overcome the challenges related to the complexities and functionalities of devices and enhance their performance. Here are some pointers to consider when designing PCB stackups.

• Application requirements: Consider the application requirements, operating environment, and factors such as signal routing speed and complexity, possibility of EMI, and power distribution. These are major factors in the PCB stackup design process.
• Number of layers and configuration: Given the complexity, most applications would require multilayered boards, rather than single- or double-layered boards. Depending on the application requirement, there could be multiple layers ranging from 4 to 20 and beyond. For RF applications or the ones with high-speed signals, consider at least four layers to accommodate proper spacing, and dedicated ground and power planes.
• Vias: Vias are connecting layers that help improve signal routing and integrity. There are standard vias that can establish connectivity across the circuit; however, they take up the routing space. Since most of these devices are compact and require HDI designs, either blind and buried or microvias serve the purpose and help achieve tight spacing, enhanced signal integrity and routing, and reduced signal paths.
• Substrate materials: The properties of materials, such as their thermal conductivity, dielectric constant, and so on, must be considered when choosing them as a substrate and weighed against the application requirements and the operating environment. While FR4 is quite common, high-frequency applications may require PTFE or Rogers.
• Grounding methods and power distribution: The design must comprise dedicated power and ground planes to create low impedance paths and serve as a reference for signals.
• Signal integrity: To achieve signal integrity and controlled impedance, carefully define trace widths, spacing, and dielectric thickness between layers. Consider routing differential pairs with controlled impedance to eliminate noise, especially for high-speed communication signals. You can also consider using microstrip traces and stripline configurations for improved impedance control and shielding.
• Electromagnetic compatibility (EMC): Any disturbance caused due to EMI must be eliminated. Also, the device must be EMC enabled, which means it must function normally in the presence of EMI. For this, the PCB stackup must be shielded with ground planes that protects sensitive signal layers from EMI. The return path for high-speed signal traces must be continuous and seamless, which can be done with the help of adjacent ground planes. Power planes must be placed next to ground planes as this creates capacitance and helps filter out noise.
• Ventilation and thermal management: Heat dissipation is an important aspect and must be handled at the design stage to prevent overheating and subsequent damage. There are certain components on the board that generate more heat than others. One can implement thermal vias for heat-generating components to transfer heat to other layers. Also, one can consider using copper layers for power plans for enhanced conductivity.

 
Are you an OEM that makes electronic products or components for modern and high-frequency applications. If yes, you would require a well-designed, customized PCB stackup to enable all the functionalities in your product. As an OEM, it is recommended to partner with a reliable PCBA services provider for such projects. Ensure you partner with an experienced and credible PCB manufacturer and assembler that caters to your requirements and offers custom options when assembling. Twisted Traces is a known name in this segment, and offers custom PCB stackups, assembling services, and PCB assembly reworks. The company uses advanced processes, materials, and fabrication techniques for PCB assembling. In case you need any further information, feel free to reach out to their team today.