Building a multilayer PCB involves a process known as pressing or lamination. Here are the basic steps involved in building multilayer PCBs, specifically focusing on the pressing process:
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Prepreg and Core Preparation: Prepreg, a sheet of fiberglass pre-impregnated with uncured resin, and core layers (thin copper-clad laminates) are prepared based on the desired number of layers in the PCB.
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Layer Stacking: The layers of prepreg and core are stacked according to the PCB design, with the copper layers aligned, and the dielectric material (prepreg) positioned between them. This creates a "layer cake" structure.
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Pressing or Lamination: The stacked layers are then subjected to high temperature and pressure in a lamination press. The heat and pressure cause the prepreg to flow, bonding the layers together and ensuring that the resin fully saturates the fiberglass and bonds with the copper layers. This process cures the resin, turning the stack into a single solid structure.
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Cooling and Trimming: After the pressing process, the multilayer board is allowed to cool. Excess resin may be trimmed from the edges, and the panel is usually cut into individual PCBs.
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Drilling and Plating: After pressing, the PCBs undergo drilling to create holes for vias and through-hole components. The holes are then plated with copper to establish electrical connections between the layers.
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Final Processing: The PCBs are then processed through standard steps such as solder mask application, surface finish, and silk screen printing.
It's important to note that the pressing or lamination process is critical to the reliability and performance of multilayer PCBs. Proper control of temperature, pressure, and time during lamination is essential to ensure that the layers are securely bonded and free from delamination or other defects.