Production Process of Multilayer Buried and Blind Hole PCBs
- Iva Leung
- Jan 14, 2024
- 2 min read
Multilayer buried and blind hole PCBs find applications in high-tech fields such as communication antennas, computers, industrial control systems, automobiles, household appliances, microelectronics, and medical instruments. Ever wondered how these complex multilayer printed circuit boards (PCBs) are made? Today, let's explore the production process of multilayer buried and blind hole PCBs through insights shared by our ceramic substrate expert.
In PCB manufacturing, there are three types of holes on multilayer boards: through-holes, buried holes, and blind holes. Blind holes are located on the top and bottom surfaces of the PCB, with a certain depth. They are used to connect surface traces with inner layer traces, and their depth usually does not exceed a certain ratio (diameter). Buried holes, on the other hand, are created within inner layers and are not visible on the outer surfaces. They are used for interconnecting signals within the inner layers and are commonly employed in devices like mobile phones and PDAs. Buried holes reduce the likelihood of signal interference, maintain the continuity of transmission line impedance, and save routing space, making them suitable for high-density and high-speed circuit board designs.
When designing multilayer buried and blind hole PCBs, a combination of these three types of holes is often utilized. Components such as large capacitors, inductors, and transistors that cannot be mounted using surface mount technology usually require through-holes (holes that traverse multiple layers and connect to the bottom layer). Buried holes and blind holes primarily serve as current paths (although through-holes can also be used).
During the manual creation of a low-level schematic for a multilayer PCB, ensuring hole alignment is crucial. A commonly used method for achieving precision involves taking a transparent plastic sheet, marking the positions of all holes and solder pads on it, covering it with a copper foil paper, and shining light from below. This process allows for the tracing of pads and holes, creating a well-aligned schematic. The hole design is based on the circuit requirements. If a circuit cannot be completed on one layer, metal-plated holes are used to route the circuit to the back layer.
In general, the routing on both sides of the PCB should be straight and avoid parallel routing where possible.
This summarizes the experience shared by our ceramic substrate expert regarding the production of multilayer buried and blind hole PCBs. It is evident that the manufacturing process for these boards is intricate and demands advanced technical expertise.
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