How do multilayer PCBs work?

Multilayer PCBs work by sandwiching multiple layers of conductive and insulating materials together to form a single circuit board with a higher density of components and traces. The layers of the multilayer PCB are connected together through plated through-holes, which are small holes drilled through the board and coated with a thin layer of conductive material. 

The process of manufacturing a multilayer PCB typically involves the following steps:

1. Layer Stackup: The first step in manufacturing a multilayer PCB is to design the layer stackup, which determines the number of layers, the order of the layers, and the thickness of each layer. 

2. Lamination: After the layer stackup is designed, the layers of conductive and insulating materials are pressed together and bonded with heat and pressure to form a single board.

3. Drilling: Next, small holes are drilled through the board at specific locations where the layers need to be connected, known as plated through-holes.

4. Plating: The plated through-holes are then coated with a thin layer of conductive material, typically copper, to create a connection between the layers.

5. Etching: The board is then etched to remove the unwanted conductive material, leaving behind the desired traces and connections.

6. Solder Masking: The board is then coated with a solder mask, a protective layer that covers the traces and connections, leaving only the areas where components will be soldered exposed.

7. Component Placement and Soldering: Finally, electronic components are placed and soldered onto the board, and the multilayer PCB is ready for use.

In summary, multilayer PCBs work by providing more layers for routing connections, which allows for a higher density of components and improved signal integrity. They are commonly used in complex electronic devices such as smartphones, computers, and medical equipment.