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Microvias are made using specialized manufacturing processes that involve precise drilling and plating techniques. These processes are essential for creating the small holes that connect different layers of a high-density interconnect (HDI) printed circuit board (PCB). The steps involved in making microvias include:

Drilling

•Laser Drilling: For microvias with small diameters, laser drilling is commonly used. A high-power laser is directed at the PCB material, vaporizing it and creating a hole. The diameter and depth of the hole are controlled by the laser parameters.

•Mechanical Drilling: Mechanical drilling with advanced tools can also be used to create microvias. These drills have fine tips that can accurately create small holes. Mechanical drilling may be preferred for larger microvias or where precision is critical.

Cleaning and Surface Preparation

After drilling, the PCB is typically cleaned to remove any debris or residue from the drilling process. Clean surfaces are essential for ensuring proper adhesion during subsequent steps.

Desmear and Plasma Treatment

In laser-drilled microvias, the laser energy can cause resin smear or resin redeposition along the walls of the hole. Desmear and plasma treatment processes are used to remove these residues and create a clean surface for plating.

Electroless Copper Deposition

A thin layer of electroless copper is deposited on the walls of the microvias. This copper layer acts as a conductive barrier and facilitates the subsequent electroplating process.

Electroplating

The microvia is electroplated with copper to build up the conductive path. The electroplating process deposits a thicker layer of copper on top of the electroless copper, filling the microvia and creating a continuous conductive path between layers.

Planarization

The surface of the PCB may undergo planarization processes, such as chemical mechanical polishing (CMP), to remove excess copper and ensure a smooth, even surface.

Structural Build-Up

Microvias are integrated into the overall HDI PCB design, which includes the build-up layers. The build-up layers may involve the addition of prepreg and core materials, as well as the creation of additional microvias and traces.

Additional Processing

Depending on the specific design requirements, the PCB may undergo additional processes, such as solder mask application, component placement, soldering, and testing.

The exact sequence and details of these steps can vary based on the PCB manufacturer's processes and the specific design of the HDI PCB. It's important to note that creating microvias requires precision and expertise to ensure the integrity and reliability of the final PCB. Designers and manufacturers work closely together to optimize the microvia design and manufacturing process for the intended application.