Role of a Buried Via in Multilayer PCBs
A buried via in multilayer PCBs is an effective way to increase routing density, reduce the number of layers and board size, and improve signal integrity. The main challenge is managing the parasitic effects of vias at higher frequencies, which include increased insertion loss, impedance mismatching, and signal reflections. By ensuring proper design of the via and its surrounding structures, these issues can be minimized.
Through-hole (TH) and blind vias are essential tools in a PCB designer’s arsenal. In addition to their physical advantages, they offer a wide range of functional and performance benefits for both PCB designs and manufacturing processes. However, it’s important to understand the differences between these via types and how they can be used effectively in various applications.
A buried via is a hole that connects a copper layer in one of the inner layers without passing through the outer surface. This type of via is a specialized version of a regular through-hole, and it’s often referred to as an internal connection or blind soldering hole. Buried vias are a vital component of high-performance HDI boards, where they are used to route signals between different internal layers without connecting the outer surfaces.
Like through-holes, blind and buried vias require precision drilling to connect specific layers while not penetrating the outer surface of the PCB. This process is usually done using mechanical drilling with tungsten carbide drill bits, rotating at speeds of 50,000 to 300,000 RPM. The holes are then plated with copper.
What is the Role of a Buried Via in Multilayer PCBs?
In addition to the drilling and plating steps, both blind and buried vias need to be carefully designed to optimize signal integrity. This is done by minimizing the length of the signal paths, which can be achieved by backdrilling (removing unused sections of the via barrel) or via fencing. Lastly, it’s critical to ensure that the alignment of the layers during the production process is accurate to prevent gaps and short circuits.
Buried vias are an excellent option for many modern PCB designs, as they enable designers to reduce the amount of copper used and provide a more dense board. They also allow designers to use advanced technology such as HDI, which can help maximize component placement and reduce overall size and weight of the device.
Another advantage of buried via is their lower cost than through-holes. In the manufacturing process, burying vias requires fewer drilling and plating steps and can result in significant cost savings. In turn, this can help the overall costs of the final product.
In addition to the cost-saving advantages of buried vias, they also allow manufacturers to utilize a faster production process by skipping steps involved in making through-holes. This means that a final PCB can be made much more quickly and at a lower cost. This can be particularly beneficial in fast-turn applications. However, the process can still be challenging if not handled properly, so it’s important to have tight control over the manufacturing and production processes.