1. Through-holes are one of the most common types of circuit board features. These holes are visible by simply holding the PCB up to the light and are called “through-holes”. This type of hole is the simplest to create, as it only requires drilling or laser cutting directly through the circuit board, which keeps costs relatively low. However, not all circuit layers require connections through these holes.

For example, imagine a six-story house where I own the third and fourth floors. I intend to design an internal staircase connecting only these two floors. This effectively links the fourth floor space with the staircase spanning from the first to the sixth floor, optimizing space usage.

To enhance PCB circuit layer space utilization, the “blind hole” process was developed. Special attention must be paid during production to ensure the drilling depth (Z-axis) is precisely calibrated. However, this method frequently encounters challenges in hole electroplating, leading to its limited adoption among manufacturers.

3. It is also possible to drill holes in advance for the circuit layers that need to be interconnected. Then, these layers are glued together, requiring precise positioning and alignment devices.

4. Connections between any circuit layers inside the PCB that are not linked to the outer layers cannot be achieved through post-bonding drilling. Instead, these connections must be drilled during the creation of individual circuit layers. Initially, they are partially glued to the inner layer, then undergo electroplating, and finally all layers are bonded together.

5. This production process is more labor-intensive compared to the previous methods, making it the most expensive in terms of manufacturing costs. Typically, this process is used exclusively for high-density (HDI) circuit boards to maximize usable space across various circuit layers.