Explorar os detalhes de uma placa PCB de 3 camadas

The PCB structure comprises outer layers (top layer + bottom layer) and inner layers (copper layer + insulating layer + copper layer). When determining the number of layers, the outer layers are counted as 2, while the inner layers are determined by the quantity of copper layers, often existing in even numbers. However, a PCB de 3 camadas is an exception, with only one inner copper layer used for circuit layout to facilitate component connections. To gain a clearer understanding of this circuit structure, let’s explore its details alongside FS Technology!

3 Layer PCB Stackup

Type 1: With Ground Plane

In high-speed digital and mixed-signal circuits, addressing signal integrity is of paramount importance. Configuring an inner layer as a ground plane is a prudent choice, with the typical stack-up structure being: Signal Layer + Ground Plane + Signal Layer.

This three-layer PCB with such a stack-up structure offers multiple advantages. Firstly, the ground plane serves as a reference for routing control, aiding in ensuring proper signal guidance. Secondly, the ground plane acts as a shield, effectively reducing electromagnetic interference (EMI). Most importantly, utilizing a dedicated ground plane facilitates ease of implementing impedance control, thereby maintaining signal integrity, avoiding distortion, and mitigating common high-frequency and high-speed signal issues like delay.

Type 2: With Split Power Plane

Mixed voltage design is suitable for components that require different voltage levels to ensure power isolation and prevent voltage conflicts. To achieve this, a typical hierarchy involves a power isolation layer (VCC and VDD), with the stack-up structure being: Signal Layer + Power Isolation Layer + Signal Layer.

Signal routing can easily take place on the first and third layers without interference from power lines. This design is particularly effective in radio frequency (RF) applications, as power isolation is crucial for maintaining signal quality.

Type 3: With Buried Signal Plane

The generation and dissipation of noise in circuits adhere to the law of energy conservation, typically stemming from energy transformations such as electron movement and electromagnetic radiation. Eventually, this noise is released in the form of heat, known as Joule heating. Although it is a common occurrence, both power loss and heat release are detrimental to circuits and require measures to manage and minimize them.

An effective stacking strategy: Ground Layer + Signal Layer + Ground Layer. The outer layers serve as ground planes, providing a uniform ground reference that aids in reducing signal noise. This is a common practice in electronic design. Precise control over the inner signal layer allows for optimization of signal transmission paths, enhancing signal reliability, and reducing noise interference.

3 Layer PCB Design Key Points

Seleção de materiais

Choosing the right materials can not only improve performance but also save a significant amount of cost. One common option is FR4 material, which is a composite material consisting of glass fiber woven fabric impregnated with flame-retardant epoxy resin. It allows you to strike the best balance between substrate performance and cost. Alternatively, for high-frequency circuits, you can leverage PTFE’s electrical insulating properties and low dielectric constant to maintain signal stability. For high-power applications, opting for metallic materials to manufacture a 3-layer PCB is often more suitable as it meets the mechanical stability requirements while enhancing heat dissipation capabilities.

Circuit Layout

Starting with the right design software can save you a significant amount of time and effort. For commercial projects, using KiCad and Altium is a good choice. 3-layer PCB circuit design is quite similar to traditional designs, including component placement, routing, and stack-up design. Following Directrizes de conceção de PCB will help you navigate this process more effectively. Here are some tips:

When designing digital and analog circuits, it’s often a good practice to separate them. This helps ensure that fast-switching digital components and high-current signals don’t interfere with analog components or introduce noise. However, in a 3-layer structure with limited inner layers, you can employ a strategy of segmenting the power layers to flow in different areas.

To achieve better signal transmission and minimize electromagnetic interference, an effective strategy is to keep critical signals away from inner layers and route them to the outer layers. This approach reduces the area of the signal loop on one hand and, on the other hand, the even copper planes on the outer layers can serve as reference planes for signals. In traditional multi-layer circuits, routing critical signals to the outer layers often involves passing through insulating layers, which increases signal transmission delay. However, for a 3-layer PCB board, you can choose the side without insulating layers for your connections.

DRC and DFM

Even in relatively simple three-layer PCB structures, relying on empirical methods to discover and correct potential issues is not recommended, especially in large-scale batch projects. Even minor oversights can lead to production delays or quality issues. To ensure accuracy and efficiency in your design, a reliable approach is to utilize DRC and DFM. These tools effectively verify details such as trace widths, spacing, and clearances, helping you adhere to the guidelines and specifications provided by manufacturers.

Should You Build a 3-Layer Circuit Structure

When you search for 3-layer PCB online, you may come across content that highlights their advantages and guides consumers, such as flexibility, circuit density, compact size, and more. However, one crucial fact needs clarification: these advantages are in comparison to 2-layer PCB, but this should not be your sole determining factor.

So, what do designers base their choice of layer count on when constructing circuits?

This depends on two aspects: electronic complexity and cost. As the number of layers in a circuit increases, circuit density can be enhanced, allowing for more functionality. However, an increase in layers also means an increase in cost. In other words, when we choose to use a 3-layer PCB, a necessary condition is that the 2-layer PCB cannot meet the electronic requirements, right?

This might seem reasonable, but you’re overlooking a critical issue: the construction cost of a 4-layer PCB and a 3-layer PCB is almost the same, or even identical. When faced with two products, both priced the same, but one offering greater functionality, how would you make your choice? I need not elaborate further on this, right? This is also why there is hardly any essential need for 3-layer PCB to exist.

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