Blind Vias Affect Signal Integrity
As component lead pitches have become increasingly fine and compact, PCB designers have had to find ways to increase the density of connections. This is where blind and buried vias come in, as they provide space-saving advantages to help engineers design more efficient and effective electronic devices. But how do these advanced via types affect signal integrity? In this blog post, we’ll take a look at the different aspects that can influence the performance of a blind and buried via.
The first step in creating a blind via is to drill the hole. This can be done manually or using a CNC machine. The key is to ensure the holes are accurate and do not touch any other circuits on the board. Then the holes are filled with copper to make them conductive. The last step is to make sure that the drilled holes are properly aligned with the intended layers and are not positioned too close together. This will prevent signal interference or degradation.
There are several ways to create a blind via, including manual drilling, laser drilling and sequential lamination. Laser-drilled blind vias use an eximer laser to cut through the copper and underlying dielectric material in a single pass, making it a fast and cost-effective method. However, this process is only possible on the outermost layer of a multilayer PCB. Manually drilled blind vias, on the other hand, are often used in the inner layers of a multilayer PCB, where a larger width of circuit can be achieved.
How Do Blind Vias Affect Signal Integrity?
Another way to create a blind via is through sequential lamination, which involves passing a very thin laminate piece through the entire production cycle of a two-sided PCB. This includes drilling, etching and plating. After the plated hole has been made, it is then bonded to the other layers of the PCB stack and pressed. This is the most expensive method for forming blind vias, but it can be very effective in reducing signal interference and improving signal transmission speeds.
The cheapest method for forming blind and buried vias is controlled-depth drilling, which uses a mechanical drill to create the holes. The drill is programmed to only penetrate the outer layer of copper and underlying dielectric material without touching the copper-connecting pad in the layers below.
This technique is often used on multilayer organic BGA packages and cell phone PCBs. Controlled-depth drilling can be risky, however, as the hole must be large enough for mechanical drills to create and the area beneath must be kept free of other circuitry to avoid contaminating it with metal. The smallest width that can be drilled is therefore dependent on the size of the drilling machine and this limits the number of blind and buried vias that can be created. It also makes it difficult to perform good plating within the holes. This is why the aspect ratio of the hole must be carefully chosen.
