Designing a PCB stackup is often considered optional because PCB manufacturers can assist with stackup creation. However, the stackup is directly related to signal integrity, EMI performance, and product reliability. This makes PCB Stackup Design an essential skill for any hardware engineer. Understanding stackup principles helps you select a structure that fits manufacturing constraints while achieving optimal electrical performance.
Key Factors in PCB Stackup Design
A robust PCB Stackup Design must consider the following four elements:
1. Layer Count
Determined by routing density, signal speed, and cost.
High-frequency designs require a continuous ground plane to maintain signal integrity.
2. Number of Power and Ground Planes
Additional planes improve return paths, reduce noise, and stabilize reference impedance.
3. Layer Order
The sequence of signal layers, power planes, and ground planes is central to achieving low EMI and stable impedance.
4. Dielectric Thickness
Layer spacing affects:
- Controlled impedance routing
- Plane capacitance
- Crosstalk
- High-frequency losses
RF and Digital Considerations in PCB Stackup Design
Traditional RF Pcb Design often use 2-layer structures with a full ground plane and an external metal enclosure.
However, modern devices require compact form factors, driving the adoption of multi-layer stackups—especially when RF and digital circuits are integrated on the same PCB.
Essential Principles for High-Performance PCB Stackup Design
Signal Layers Should Be Close to Reference Planes
To ensure stable return paths and reduce EMI:
- Signal layers must be adjacent to ground planes.
- Power planes should be tightly paired with ground planes.
This is the foundation of a good PCB Stackup Design.
Stripline Preferred for High-Frequency Signals
Stripline offers superior shielding compared to microstrip because the trace is sandwiched between two ground planes.
Multiple Ground Planes Improve EMC
More ground layers reduce impedance and common-mode noise, though they increase manufacturing cost.
PCB Stackup Design for 4-Layer Boards
To illustrate how to choose the best structure, let’s begin with several common 4-layer PCB stackup design options (from top to bottom):
(1) Siganl_1 (Top) → GND (Inner_1) → POWER (Inner_2) → Siganl_2 (Bottom)
(2) Siganl_1 (Top) → POWER (Inner_1) → GND (Inner_2) → Siganl_2 (Bottom)
(3) POWER (Top) → Siganl_1 (Inner_1) → GND (Inner_2) → Siganl_2 (Bottom)
Option 3 should not be used because the power layer and ground layer are poorly coupled.
How to choose between Option 1 and Option 2?
- In most cases, engineers choose Option 1, since components are mainly placed on the Top layer, and the stackup provides balanced manufacturability and performance.
- If components are placed on both Top and Bottom, and the inner power-ground spacing is large (poor coupling), then choice depends on routing density:
- If Bottom layer has fewer traces → Option 1 allows large copper pour for better POWER coupling
- If most components go on Bottom → Option 2 becomes the better choice
When using a symmetric structure where POWER and GND are already tightly coupled (as in typical manufacturer recommendations), Option 1 is preferred.
PCB Stackup Design for 6-Layer Boards
After understanding the 4-layer board, let’s evaluate several 6-layer PCB stackup design combinations.
Option 1:
Siganl_1 (Top) → GND (Inner_1) → Siganl_2 (Inner_2) → Siganl_3 (Inner_3) → POWER (Inner_4) → Siganl_4 (Bottom)
Issues:
- Power and ground layers are far apart → poor coupling
- Siganl_2 and Siganl_3 are adjacent → high crosstalk risk
Option 2:
Siganl_1 (Top) → Siganl_2 (Inner_1) → POWER (Inner_2) → GND (Inner_3) → Siganl_3 (Inner_4) → Siganl_4 (Bottom)
Power-ground coupling improves, but new issues remain:
- Siganl_1 adjacent to Siganl_2
- Siganl_3 adjacent to Siganl_4 → Crosstalk still likely
Option 3 (Best and Most Common 6-Layer Stackup)
Siganl_1 (Top) → GND (Inner_1) → Siganl_2 (Inner_2) → POWER (Inner_3) → GND (Inner_4) → Siganl_3 (Bottom)
Advantages:
- Power and ground layers are tightly coupled
- Every signal layer is adjacent to a reference plane → excellent isolation
- Siganl_2 is sandwiched between GND and POWER → ideal for high-speed signal transmission
- Two internal reference planes provide strong shielding to reduce EMI
Because of these factors, Option 3 is the most widely used and the most optimized 6-layer PCB stackup design.
PCB Stackup Design for 10-Layer Boards
A typical 10-layer PCB stackup design follows this order:
TOP → GND → Signal → Power → GND → Signal → Power → Signal → GND → BOTTOM
Although variations exist, stackup design is constrained by several universal principles:
- The layers adjacent to TOP and BOTTOM should be GND to enhance EMC
- Each signal layer should use GND as its reference plane
- Power rails used throughout the board should be placed on large copper planes
- High-speed, noise-sensitive, or edge-rate signals should preferably be routed on inner layers
- Avoid reference plane discontinuities to reduce EMI
This structure provides a balanced solution for high-speed, RF, and mixed-signal applications.
Conclusion
Successful PCB Stackup Design requires balancing signal integrity, EMC performance, manufacturability, and cost.High-speed and RF systems especially demand careful planning and engineering experience.These principles and practical insights help engineers minimize design iterations and improve product performance.
If you need professional PCB Stackup Design support for your next product, Tronixv can help you achieve high performance, reliability, and manufacturability contact us.
