Micro Vias Contribute to Consumer
The conductive pathways that connect electronic components and allow them to function together are created in multilayer printed circuit boards (PCBs). To establish these connections, holes are drilled completely through the layers of the board. When the holes are plated with copper, they are referred to as plated through-holes or vias.
As electronic devices become increasingly complex, the ability to connect them with each other grows ever more critical. This has led to the development of high density interconnection (HDI) PCBs. In order to achieve the increased functionality that these higher-density boards require, they must use specialized vias. These specialized vias, known as blind, buried, and micro vias are indispensable tools in the designer’s arsenal. This blog will explore what these vias are, how they work, and why it’s important to utilize them.
A micro via is a type of hole in the surface of a printed circuit board that can be used to route high-speed signals between layers. The holes are usually surrounded by dielectric material, which reduces the inductance and capacitance of the circuit, increasing its signal integrity. Depending on the application, microvias can be used either stacked or staggered.
Micro Vias Contribute to Consumer Electronics
Stacked microvias are stacked one atop another and can be found in both double-sided and single-sided PCBs. Staggered microvias, on the other hand, are positioned so that they skip a layer. Since a buried or blind microvia in a layer makes no electrical contact with the adjacent layers, it is necessary to add a stub of copper barrel to the via so that it can be soldered to another piece of metal. The stub is also important because it prevents the high-speed signal from distorting as it travels through the circuit board.
These stubs of copper are typically cut using a technique called back drilling, which is a process that removes the unused portion of a plated through-hole. This technique is particularly useful for signals that travel between different layers of the board, as it ensures that the signal is transmitted with minimal distortion.
While mechanical drilling is a cost-effective and reliable method for creating microvias, it has some limitations. It cannot create holes with precise geometries, and it can produce burrs and rough surfaces on the surface of the hole. Therefore, new technologies like UV laser drilling are constantly being developed to create more accurate microvias.
The reliability of a microvia depends on its design. The most common types of failure occur at the interface between stacked microvias and the plated interface between the via and its capture pad. These problems can be caused by thermal cycling, which puts stress on the thin copper plating. Other failure modes include voids, bumps, or dimples that can form in the filled microvia. To avoid these failures, it is important to choose a manufacturer that offers HDI microvias that are designed with the appropriate aspect ratio enforced by the design. It is also recommended to limit the number of stacked microvias to two layers.
