Compact, high-performance PCBs have various design options. One of them is the cavity PCB. This board uses internal pockets to optimize functions and size, among other benefits. Here, you’ll learn its features, advantages, and key applications in today’s electronic products.
What is a Cavity PCB?
A cavity PCB is a printed circuit board with one or more cavities. The manufacturer deliberately creates the cavities in the substrate. They serve various functions, from mounting electronic components to dissipating heat.
The pockets are usually open or embedded. Open types are recessed areas on one of the PCB’s surfaces. They typically mount components, but can also serve as heat sinks if plated with copper.
Embedded cavities sit inside the layers, enclosed and protected from external damage. They mainly mount passive parts and chips. Cavity depths also vary based on their application goals.
Shallow types reduce component height to produce slimmer PCBAs. On the other hand, deeper cut-outs mount larger-sized parts. They also help manage temperatures in high-speed boards.
How is a Cavity PCB Made?
The board’s manufacturing steps are similar to conventional types. The steps only differ in the pocket-creation process. Manufacturers use these technologies to produce the recesses: milling, laser ablation, and sequential lamination.
Controlled Depth Milling
A precision CNC router engraves the laminated substrate, scooping material to create the desired recess depth and size. This method is economical but less precise. Sometimes, PCB fabricators use it alongside laser ablation.
Laser Ablation Method
This method uses a high-energy laser to evaporate the board material from the marked area. It offers higher precision but costs more. Thicker laminates with deeper cut-outs may require CNC machine engraving before using the laser to remove the remaining part.
Sequential Lamination
Sequential lamination involves stacking low-flow or no-flow sheets to create the pocket structure. This method takes time, increasing the board’s fabrication cost. It also requires choosing the pre-preg laminate to ensure proper bonding.
Cavity PCB Board Types
A PCB cavity must comply with IPC standards (2228 and IPC 6012F). The standards outline acceptability criteria based on the recessed area features. Consequently, we place the boards into these three groups.
Type 1 Cavity
This type of cavity has no metalized surfaces, whether on the floor or walls. The space it creates accommodates various components, such as sensors. It does so without increasing the board’s height.
Type 2 Cavity
These have metallization on the floor or walls, but not both. Embedded cavities with metalized floors or ceilings fall into this group. Their copper usually requires etching for component mounting and wire bonding.
Type 3 Cavity
The recessed part has solid copper on the floor and walls. This design makes the recess suitable for heat-sinking. The sink usually embeds in the board, with the metallized surfaces helping to draw and dissipate the heat.
Resource: https://www.researchgate.net
What are The Advantages of Cavity PCBs?
The board offers various benefits depending on the required function and reliability features. These advantages explain its preferred use in modern electronics.
Reduced PCBA Height
Using recessed sections to mount components reduces their height. It enables designers to create low-profile PCBAs for thin devices or enclosures. Such boards are suitable for compact devices like wearable products.
Improved Routing Efficiency
Cavities allow PCB manufacturers to directly mount components to a signal trace and other copper layer, eliminating the need for via connections. It reduces connection distances, leading to better electrical performance.
Better Thermal Management
Designers use solid copper cavities to help dissipate heat and improve a board’s thermal performance. The heat sink is usually an embedded component like a copper coin.
Component Protection
Components lie low, protected from external forces and damage. Embedding components in enclosed cavities increases this protection, making the circuit board more reliable. It also means a longer-lasting board and application device.
Cavity PCB Manufacturing Challenges
The circuit boards are more challenging to design and fabricate. They have features that require specialized design steps and fabrication equipment. The following are difficulties manufacturers encounter when creating or assembling the PCBs.
Manufacturing Complexity
They require a different approach to create, such as knowing where to place the cavities, their sizes, depth, and more. Sometimes, the designer must add new layers to meet new needs. These requirements present design and tooling challenges.
Increased Costs
Cavities make circuit boards more demanding to fabricate, mount with parts, and test. These boards are, therefore, generally more expensive than standard circuit boards.
Structural Strength
The recessed parts reduce the substrate’s structural integrity of rigid PCBs. In some cases, the design may not suit the application. In others, the designer must employ strengthening strategies.
Resource: https://forum.kicad.info
Factors to Consider When Designing a Cavity PCB
Creating the PCB for manufacturing requires a careful approach. Designers must also understand the board’s cavity-creation requirements, which include the following.
Material Characteristics
The substrate must support the inclusion of pockets. That means choosing a material that offers good mechanical strength and dielectric properties.
Mechanical strength reduces the chances of warping. On the other hand, a low and stable dielectric constant (Dk) value improves signal integrity. Other important properties include thermal stability and resistance to environmental factors like humidity.
Cavity Placement and Clearance
The pockets must not interfere with other board parts, including traces. Designers must, therefore, ensure adequate clearance without affecting miniaturization needs.
Cavity Size and Depth
Pockets can reduce or increase resonance, interfering with signal quality. These issues arise if cavity designs are not of the correct size. Depth can also interfere with the board’s structural integrity. It must match the PCB’s thickness and material characteristics.
Resource: https://www.mdpi.com
Cavity PCB Applications
The compact nature of the cavity circuit board makes it a good choice in many of today’s electronic devices and systems. These are applications where space is premium and weight reduction is critical. They include the following.
- High-speed computing systems
- Wearable tech devices
- Mobile or portable electronic devices
- High-performance automotive PCBs
- Medical devices like implants
- High-power motor control modules
- Renewable energy and other DC power systems
- High-frequency communication systems (RF and microwave)
PCB cavities in the above applications will have varying functions, depending on the usage needs. For instance, they may control board size for sleeker devices or increase heat dissipation in power circuits.
Conclusion
A cavity PCB has recessed sections on the surface or embedded pockets in the inner layers. These contain components, reducing the board’s height and saving assembly space on the outer layers. Understanding its design requirements helps optimize it for your application, ensuring your project’s success.
