Before discussing embedded PCBs, let's first talk about the evolution of PCB embedded components and their sizes, from large to small. What is the main reason we celebrate embedded PCBs?

Embedded PCBs can be made by placing discrete components inside the core of the PCB or manufacturing PCB embedded components during the PCB manufacturing process.

Embedded resistor forming

Resistors are part of embedded passive PCBs and are passive components. PCB embedded resistors or PCB buried resistors can be made through molding or manufacturing techniques. Simply put, development, etching, and peeling are common processes. Then, the first layer of thin film or thick film resistive copper foil composed of copper and resistance alloy (such as Nicr) is processed like normal development, etching, and stripping manufacturing steps. Ultimately, we will obtain a resistor. In short, we are manufacturing resistors, just like we are manufacturing tracks and pads. The only difference is the use of special thin or thick films, which are a combination of resistance alloy and copper foil. When comparing thin film and thick film technologies, thin film technology is more convenient than thick film technology.

Embedded inductor forming

Embedded or buried inductors can be molded or manufactured as part of the same process as traces and pads. Consider a four layer PCB, where the inductor circuit will have spiral or square winding structure tracks that exist parallel to all layers to form embedded or buried inductors. Compared with the other two molding technologies of resistors and capacitors, the concept of molding/manufacturing technology for embedded or buried inductors is easy to understand.

Embedded capacitor molding

Embedded or buried capacitor: A layer of capacitive element film is placed between the power plane and ground plane inside the PCB, called an embedded capacitor. A thin dielectric film is placed between two conductive copper layers, like a sandwich structure. The manufacturing of embedded capacitors (part of the embedded capacitor PCB) can be completed in three steps. The first step is to add a bottom electrode, which is first placed using nickel foil. The second step (adding an intermediate layer) is to add a thin dielectric film on the nickel foil, such as barium titanate formed by sputtering. The third step (adding a top electrode) is to place a copper top electrode on top of it. This is the formation or manufacturing method of embedded or buried capacitors.

Placement of components

In the placement methods of active and passive components, we use separate components of resistors and capacitors. Inductors are different from resistors or capacitors. For all these active and passive components, we need to create a cavity process for placing them, which should be addressed in the design phase and gaps in the DFM phase. This is a complex process that requires additional skills and time to place all PCB embedded components in the correct positions. Once placed, it cannot be replaced under any circumstances, even in the case of defective components that cannot be replaced by this method. This seems to be one of the drawbacks of the embedded PCB placement method. When it comes to the placement of ICs, we also have the same process. We need a cavity to place the IC inside the PCB.

Adding integrated copper coins or solid copper materials inside or below the PCB surface is called embedding in the PCB. Embedded copper coin PCB is used to maintain thermal management and heat dissipation of PCB. This can be achieved through various technologies, such as heat sinks, thermal pads, thermal through holes, solid copper, or copper infusion designs. All of these technologies can be used individually or in combination, and they help reduce heat dissipation on printed circuit boards. The types of embedded copper coin PCBs are as follows.

The buried copper coin method involves placing copper coins inside the PCB, which cannot be seen through the outer layer of the PCB. In this method, heat from the outer layer of the PCB (generated due to high-density current flow) is transferred to the inner copper coin through thermal vias, and since copper is a good thermal conductor, this heat can diffuse throughout the entire copper, thereby reducing heat. In addition, they can be transferred to the other side of the heat sink or power/ground copper outer layer.

After PCB stacking, perform cavity processing and place embedded copper coins into the cavity. Fixing copper coins to the PCB helps with thermal management and heat dissipation. For embedded copper coins, we have different coin structures that are placed from the top to the bottom of the PCB.

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