Introduction to PCB Stackup

A PCB stackup refers to the arrangement of copper and insulating layers that make up a printed circuit board (PCB). It is a critical aspect of PCB design as it determines the board’s electrical properties, mechanical strength, and manufacturability. In this article, we will delve into the standard stackup for multilayer PCBs provided by RAYPCB, a leading PCB manufacturer.

Why is PCB Stackup Important?

PCB stackup plays a crucial role in the performance and reliability of electronic devices. Here are some reasons why PCB stackup is essential:

1. Signal Integrity: The arrangement of layers in a PCB stackup can significantly impact signal integrity. Proper stackup design minimizes crosstalk, electromagnetic interference (EMI), and signal reflections, ensuring reliable signal transmission.

2. Impedance Control: PCB stackup influences the characteristic impedance of transmission lines. By carefully selecting the dielectric material and controlling the thickness and spacing of layers, designers can achieve the desired impedance for high-speed signals.

3. Power Distribution: The placement of power and ground planes in the stackup affects the distribution of power to components. A well-designed stackup ensures a low-impedance power delivery network, minimizing voltage drops and power supply noise.

4. Manufacturability: The choice of materials and the number of layers in a PCB stackup impact the manufacturing process. A standard stackup that adheres to manufacturing guidelines ensures high yield and reduces production costs.

RAYPCB Standard Stackup for Multilayer PCBs

RAYPCB offers a standard stackup for multilayer PCBs that combines optimal electrical performance with cost-effective manufacturing. Let’s explore the details of this stackup.

Layer Configuration

The standard stackup for multilayer PCBs at RAYPCB consists of the following layers:

Layer	Description
Top Layer	Signal layer for component placement and routing
Ground Layer	Solid ground plane for signal return and shielding
Inner Layer 1	Signal layer for routing
Power Layer	Solid power plane for power distribution
Inner Layer 2	Signal layer for routing
Bottom Layer	Signal layer for component placement and routing

This six-layer stackup provides a balance between signal integrity, power distribution, and manufacturing efficiency.

Material Selection

RAYPCB uses high-quality materials in their standard stackup to ensure reliability and performance. The key materials used are:

1. Copper: The conductive layers in the PCB are made of copper. RAYPCB uses Copper Foils with a thickness of 1 oz (35 μm) for the outer layers and 0.5 oz (17.5 μm) for the inner layers. The copper thickness can be adjusted based on the specific requirements of the project.

2. Dielectric: The insulating material between the copper layers is called the dielectric. RAYPCB uses FR-4, a glass-reinforced epoxy laminate, as the standard dielectric material. FR-4 offers good mechanical strength, thermal stability, and electrical insulation properties.

3. Solder Mask: The top and bottom layers of the PCB are coated with a solder mask, which acts as an insulating and protective layer. RAYPCB offers various solder mask colors, including green, red, blue, and black, to meet different design preferences.

Layer Thickness and Spacing

The thickness and spacing of layers in the PCB stackup are critical for achieving the desired electrical characteristics. RAYPCB follows industry standards and best practices to determine the optimal layer thickness and spacing.

Layer	Thickness
Copper (Outer Layers)	1 oz (35 μm)
Copper (Inner Layers)	0.5 oz (17.5 μm)
Dielectric (FR-4)	7628 (0.18 mm)
Solder Mask	0.025 mm

The spacing between layers is carefully controlled to maintain the desired impedance and minimize crosstalk. RAYPCB uses a minimum spacing of 0.15 mm between signal layers and 0.2 mm between signal and plane layers.

Via Technology

Vias are conductive pathways that connect different layers in a PCB. RAYPCB employs advanced via technology to ensure reliable interconnections and minimize signal degradation.

• Through-hole vias: These vias extend through all layers of the PCB and are used for connecting components and routing signals between layers. RAYPCB offers various drill sizes and pad diameters to accommodate different design requirements.

• Blind and Buried Vias: Blind Vias connect an outer layer to an inner layer, while buried vias connect two inner layers without extending to the outer layers. RAYPCB can fabricate blind and buried vias to optimize routing density and signal integrity in complex designs.

Impedance Control

Impedance control is essential for high-speed digital circuits and RF applications. RAYPCB offers impedance-controlled stackups to meet specific impedance requirements.

• Controlled Impedance: RAYPCB can fabricate PCBs with controlled impedance traces by adjusting the trace width, thickness, and spacing relative to the reference plane. Common impedance values include 50Ω, 75Ω, and 100Ω, but custom values can be accommodated.

• Differential Pairs: For differential signaling, RAYPCB can route traces as differential pairs with a specific impedance and maintain a consistent spacing between the traces to minimize skew and ensure signal integrity.

Benefits of RAYPCB Standard Stackup

Using RAYPCB’s standard stackup for multilayer PCBs offers several benefits:

1. Proven Design: The standard stackup has been extensively tested and optimized for electrical performance and manufacturability. It provides a reliable starting point for most PCB designs.

2. Cost-Effective: By adhering to a standard stackup, RAYPCB can streamline the manufacturing process and reduce production costs. This translates to cost savings for customers.

3. Faster Turnaround: With a standard stackup, RAYPCB can expedite the fabrication process, leading to shorter lead times and faster delivery of finished PCBs.

4. Scalability: The standard stackup can be easily adapted to accommodate different PCB Sizes and layer counts. This scalability allows for flexibility in design while maintaining the benefits of a standardized approach.

Designing with RAYPCB Standard Stackup

When designing a multilayer PCB using RAYPCB’s standard stackup, consider the following guidelines:

1. Component Placement: Place components on the top and bottom layers of the PCB, ensuring proper clearance and accessibility for assembly and testing.

2. Signal Routing: Route critical signals on the inner layers, preferably adjacent to the ground or power planes. Use appropriate trace widths and spacings to maintain signal integrity and minimize crosstalk.

3. Power Distribution: Place power planes near the center of the stackup to provide a low-impedance power distribution network. Use multiple power planes if required to support different voltage levels.

4. Ground Planes: Include solid ground planes to provide a stable reference for signals and shield them from external noise. Use stitching vias to connect ground planes across layers and minimize ground loops.

5. Via Placement: Optimize via placement to minimize signal reflections and improve signal integrity. Avoid placing vias in critical signal paths or near sensitive components.

6. Design Rule Check (DRC): Perform a thorough DRC to ensure that your design complies with RAYPCB’s manufacturing guidelines and the standard stackup specifications.

By following these guidelines and leveraging RAYPCB’s standard stackup, you can create robust and reliable multilayer PCBs for your projects.

Conclusion

RAYPCB’s standard stackup for multilayer PCBs provides a solid foundation for designing and manufacturing high-quality PCBs. By offering a well-defined layer configuration, carefully selected materials, controlled impedance options, and advanced via technology, RAYPCB ensures that your PCBs meet the highest standards of electrical performance and reliability.

When designing your next multilayer PCB, consider using RAYPCB’s standard stackup to benefit from its proven design, cost-effectiveness, and faster turnaround times. With RAYPCB as your trusted PCB manufacturing partner, you can focus on innovation while leaving the complexities of PCB fabrication to the experts.

Frequently Asked Questions (FAQ)

1. Q: Can I modify the standard stackup to suit my specific design requirements?
   A: Yes, RAYPCB’s standard stackup serves as a starting point, and modifications can be made to accommodate specific design needs. However, deviating from the standard stackup may impact the manufacturing process and lead times.

2. Q: What is the maximum number of layers supported in RAYPCB’s standard stackup?
   A: RAYPCB’s standard stackup for multilayer PCBs consists of six layers. However, they can fabricate PCBs with higher layer counts based on customer requirements.

3. Q: How does RAYPCB ensure the quality and reliability of their PCBs?
   A: RAYPCB follows strict quality control processes throughout the manufacturing process. They use high-quality materials, advanced manufacturing equipment, and rigorous testing procedures to ensure that every PCB meets the highest standards of quality and reliability.

4. Q: What is the typical lead time for multilayer PCBs using RAYPCB’s standard stackup?
   A: The lead time for multilayer PCBs using RAYPCB’s standard stackup varies depending on the complexity of the design and the quantity ordered. However, RAYPCB strives to provide faster turnaround times compared to custom stackups. Contact RAYPCB for specific lead time information.

5. Q: Can RAYPCB provide assistance with PCB design and layout?
   A: Yes, RAYPCB offers PCB design and layout services to assist customers in creating optimal PCB designs. Their experienced engineers can provide guidance on component placement, signal routing, and stackup design to ensure the best possible performance and manufacturability.