What Is a Stacked Microvia?
If you often find yourself in conversations discussing PCBs, one of the topics that is bound to come up is ‘Microvias’.
When designers begin working on their first PCB design, they usually do not know a lot about the different PCB design styles and layouts used in modern day such as the stacked microvia. Stacked microvias are installed by adding via holes that connect to underlying layers. This allows for great flexibility in routing layers and helps to minimize congestion and reduce cost.
This guide will help you better understand why to add a stacked microvia layout to your PCB design.
Stacked Microvia: Overview
A stacked microvia in PCB is a type of via that allows multiple layers to connect with one another. It is also known as a through-hole interconnect or cross-hole interconnect. The stacked microvia has the same purpose as a normal via, which is to allow electrical connections between different layers of a PCB.
The stacked microvia is used when there are multiple layers in a design and each layer has traces that need to be connected with each other. It can also be used when one trace needs to be split into two or more parts in order for it to reach different layers of the board. The stacked microvia helps reduce the number of vias needed on your design and therefore reduces cost and improves signal integrity.
Stacked microvias can be found on both single-sided and double-sided boards, with the latter being more common for high-frequency circuits due to their reduced inductance characteristics. The most common type of stacked via is called a blind microvia because you cannot see the hole from the top side of the board. Blind microvias are usually used together with blind headers, which are pins soldered onto the bottom side of your PCB so you can easily connect them with wires or other components without having to use special tools or techniques.
Stacked Microvia Advantages
Stacked microvias are a new way to make electrical connections in semiconductor and microelectronic devices. They have several advantages over traditional vias:
Stacked microvias can be made by etching copper layers below the dielectric layers, using standard photomask and lithography tools. This reduces the cost of these devices because they require fewer process steps than traditional vias, which must be fabricated by depositing metal on top of the dielectric layers.
Improved Signal Integrity
The reduced number of processes required to fabricate stacked microvias makes them easier to align with other features on a chip. This improves signal integrity because there are fewer features that could cause reflections or scattering at the via location.
Stacked microvias can be easily incorporated into existing chips without requiring any changes to the manufacturing process, which means they can be added to any design at any time during production.
Minimal Impact on Board Thickness
With a traditional via, you must route all your signals and power through a single layer in order to meet minimum trace width requirements. This means that even if you have only one signal on one side of your board, you will still have to route everything through the same layer. This can be problematic for large boards where you need to conserve space for other components or keep your board below a certain thickness so it can fit into an enclosure or panel mount device such as an LCD display. With stacked microvias, however, you can route all your signals through different layers without having an impact on board thickness assuming they are not too close together.
In most cases, stacked microvias will be much smaller than traditional vias. This is because they are drilled instead of punched, which leaves no room for excess material. So even though you may need to use more stacked microvias than traditional vias to complete an electrical connection, the overall size of your PCB will remain small and compact.
Less Drilling Required
Stacked microvia drilling often requires less drilling time than traditional vias because there's no excess material to remove after punching or laser drilling. This means that they can be used in PCBs where time is critical — such as when manufacturing high-volume products like smartphones and tablets — without compromising quality or causing delays in production schedules.
Reduced Thermal Resistance
Stacked microvias have lower thermal resistance than standard vias because they are smaller and have less copper in contact with the dielectric layer above them. The lower thermal resistance reduces power dissipation in these devices, which can improve overall performance and reduce heat generation for multi-core processors in particular.
More Efficient Use of Space
Stacked microvias can be embedded within the interconnect layers of a chip, allowing more interconnects to fit within a given area than would be possible with standard vias alone. This means that chips with stacked microvias may offer higher performance while using less power than their traditional counterparts.
Applications of Stacked Microvias
In high-speed/high-power circuits, it is important to have as few microvias as possible because they add inductance and capacitance to your circuit which can cause signal integrity issues. Having fewer microvias means less inductance and capacitance, resulting in better signal quality at higher frequencies.
Stacked microvias have been used extensively in automotive, aerospace and military applications where dielectrics are not as critical as they are in other industries such as consumer electronics or medical devices. In these industries, you want as much dielectric material on your PCB as possible because it helps reduce EMI radiation from your board.
All in all, stacked microvia has become a concern, especially for PCB designers. Whether you are planning on ordering PCBs or already have your PCBs in hand, understanding the process for a stacked microvia via will allow you to confidently order and prepare for manufacturing.
Understanding stacked microvia can be a little intimidating at first, but it is something that you will get the hang of with just a bit of practice. For an in-depth learning of stacked microvias, check out Hemeixin.