As printed circuit boards continue to shrink in size, the surface area available for wires and components is becoming more and more limited. In this case, cavity PCB becomes an effective solution.
In a PCB, a cavity is defined as a hole (cutout) from the outer copper layer to the inner copper layer but does not completely penetrate the PCB. By assembling components in the cavity area, the height of the components can be reduced, making the entire circuit board more compact, and more functions and layout optimization can be realized in a limited space. At the same time, the cavity can also provide more space and increase the gap between components, thereby reducing the interference between components and improving the reliability and performance of the circuit. In addition, the cavity can also be used to increase the heat dissipation surface area, which is especially important for circuit boards with small volume and high power. By designing the heat dissipation structure in the concave cavity, the heat can be dissipated more effectively, ensuring the stable operation of the components under high load conditions.
The latest revision of the IPC standard for rigid PCBs, IPC-6012F, defines three types of recessed cavities and their acceptable criteria:
Multiple inset cavities in a PCB. [Image source: IPC]
Cavities that contain copper inside, such as traces and pads, are referred to as Type 2 cavities. If there is still some plating on the walls of the cavity, such as partially plated walls, then this will be a Type 3 cavity.
The cavity can also be completely filled with copper, sometimes called copper coining (or "coining"). This is usually done so that the area inside the PCB can act like a big heat sink; when placed under a component, it will provide significant heat transfer to the inside of the board. If a copper coin is connected to an electrical plane or placed close to a large electrical plane, it will provide significant heat transfer away from the heat source. This can also be used to bond the component to the case so that the coin and case together form a large heat sink.
Learn more about Copper Coin PCB through the following video:
In high-frequency antenna circuit boards, removing unnecessary circuit board layers can reduce the loss of high-frequency signals, which is especially important for antenna structures. Therefore, PCBs with cavities are very suitable for wireless communication applications, such as smartphones and their infrastructure. The waste heat generated by heat-generating elements can also be managed more effectively through targeted material removal.
