As we know, a printed circuit board (PCB) is constructed by layering copper foils, and the connection between different layers relies on vias. These vias, or conductive holes, are created using drilling methods to connect various circuit layers, similar to interconnected tunnels in a multilayered underground system. Understanding the purpose and principles of vias, which facilitate electrical conductivity, is crucial. Initially, holes created by drilling or laser processes do not conduct electricity. Therefore, a layer of conductive material, typically copper, must be electroplated on the hole’s surface to enable electronic movement between different copper foil layers. The original hole surface, made of resin, is non-conductive. Now that the purpose and principles of vias are clear, let’s explore different types of vias to facilitate more effective discussions with engineers.
Commonly, there are three types of vias, as follows:
Through-Hole: Plating Through Hole (PTH)
This is the most common type of via. By holding the PCB against light, one can easily identify the bright holes, known as through-holes. Through-holes are the simplest and most cost-effective to produce, as the entire PCB can be drilled with a regular drill bit or laser. However, in some cases, certain circuit layers may not require connections via through-holes, leading to potential space wastage.
Blind Hole: Blind Via Hole (BVH)
Blind holes connect the outermost layer of a PCB with adjacent inner layers through electroplated holes. However, they do not penetrate through the entire board, hence the term “blind hole.” This manufacturing process requires careful attention to the depth (Z-axis) of drilling. Blind holes can be pre-drilled in individual layers before bonding, or layers with specific connections can be drilled simultaneously. Blind holes are visible on one side of the board but not on the other.
Buried Hole: Buried Via Hole (BVH)
Buried holes connect any internal circuit layer of a PCB without extending to the outer layer. This process cannot be achieved through the drill-and-bond method; individual layers must be drilled, partially bonded, undergo electroplating, and then fully bonded. It is a more labor-intensive process and, consequently, the most expensive. This method is typically used in High-Density Interconnect (HDI) PCBs to maximize usable space in other circuit layers. Buried holes are not visible from the external surface of the board.Understanding these different types of vias helps in choosing the appropriate via type based on the specific requirements of the PCB design.
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