The Drive for Circuit Board Miniaturization & the Role of the Microvias PCB

Printed Circuit Boards (PCBs), as the center-point for electronic products, have helped in fine-tuning the conductive pathways for these products’ components. In recent times, and buoyed by the developments in the electronics market, most products are now made compact. The need for denser footprints potentially means less spaces for these routings to be done inside the products.

Luckily, microvia PCB has been introduced to help improve the routing options for electronics. When compared to some of the other vias, such as buried and blind vias, the microvias can potentially improve how routings are done on consumer electronics.

In this article, we aim to emphasize on the importance of microvias PCBs towards the ongoing campaigns for miniaturizing the footprints of electronics.

What is a Microvia in PCB?

Also known as small via or uVias, it is a type of via or hole drilled into the Printed Circuit Board (PCB). With an aspect ratio of 1:1, the hole is not expected to exceed a depth of 0.010-inch.

The function of the microvias is to be an interconnection or a medium for interconnecting between the Printed Circuit Boards (PCBs) and the High Density Interconnect (HDI) substrates.

In case you are wondering why the concept of HDI microvia became popular, it is due to the need to connect as many layers as possible. Considering that the HDI PCBs use multiple layers, the use of the uVias helps to connect the necessary layers, adjacently.

How the Microvias Makes a Difference

In an industry filled with lots of products, technological advancements and a crop of innovations, how does the microvia in PCB make any difference?

The following are some of the key ways it makes the needed difference:

  • Microvia helps to meet the demands of fitting higher Input and Output (I/O) pins and densities. This is due to the fact that multiple I/Os are now being used even in the densest circuit boards. With the microvia, it is possible to fit these I/Os perfectly in one box.
  • Microvia helps to balance the equation of having reliable PCBs with an increased functionality, affordability and lightweight design.

Attributes of the Microvias PCB

Let us talk about some of the features or characteristics that set the microvia apart and help it to bolster the functionality of circuit boards.

1. Denser Plus Complex Design Support

It may come off as absurd to say that a product has a dense footprint, and yet, it supports complex designs. It is possible if the microvia is integrated or drilled into the Printed Circuit Board (PCB).

Here is how it works:

  • The diameter of a microvia is usually less than 150 microns. Due to this smaller size, it makes it easier to fit into a circuit board.
  • When added or drilled into the PCB, the microvia helps to connect one layer of the board to the other, in an adjacent format.
  • This way, it is possible to maintain the density or limited spacing of the board, while connecting the most complex circuit designs.

2. Less Exposure to Manufacturing Defects

Manufacturing defects or design errors happen when the designer made a mistake in the process of doing the job. With microvia, these errors are limited.

Thanks to the smaller size and the use of lasers for the drilling, there is a reduced chance of having residues by the time the process is completed.

The Fabrication Processes for Microvias PCBs

There are two major processes for integrating microvia into a Printed Circuit Board (PCB). Although the laser-drilling process has become the most popular, there is still another option – stacking and pressing.

Here is a summary of some of the processes used when fabricating microvias into PCBs:

1. Drilling

The first step is to drill the microvia down to 6 or 8 mil diameters. This is keeping to the less than 150 microns (µm) of diameter.

Once the drills are made, the next step is to clean the surface.

2. Plating

The second fabrication process is to plait the microvia. Different processes, such as electroless copper, the sputtering process or electrolytic deposition can be used here.

The aim of plaiting the microvia is to prevent a couple of issues that would metamorphose into design errors. Examples of these issues are:

  • Bumps
  • Void formation
  • Dimples

Basically, plaiting the microvia PCB helps to prevent a wide range of structural dents or defects from impacting the filled via.

Once completed, the next steps would be stacking and pressing each layer onto the via.

Design Considerations for Microvias PCBs

Although you can use the microvia to improve the routing options in a PCB, it does come with some great tradeoffs. You may need to be extra careful when working on such projects to avoid making mistakes that will cost a lot to fix.

So, what are these issues?

1. Fractured Neck

This refers to the susceptibility of getting fractures near the middle of the via’s barrel. Factors that lead to this include:

  • Fractures can be sustained due to any of the following factors or exposures: mechanical shock, repeated normal cycling and strong vibration.
  • Stress concentrates on the barrel region, due to the inward curving of the copper used in the plating method for microvias.

2. Layer Limitations

It is true that microvias can connect layers and improve the routing capabilities of multilayered circuit boards. However, what is not true is that the number of layers that could be connected is limited.

Ideally, more than one layer may not be connected within the PCB, in one quick succession. The major limitation to this is the smaller aspect ratio.

The closest option towards resolving this is by fabricating higher or larger aspect ratios between 1:1 and 2:1. Although these options are better than the 0.75:1 aspect ratio of some microvias, it tends to trigger reliability concerns.

Therefore, for the best results, consider using the microvias to connect a single layer within the PCB, in succession.

The Types of Microvias in PCBs

Now that we are through with the microvia PCB definition, let us talk about some of the options you got.

Note also that despite the different types of microvias you can find out there, the major difference between most of them is how they are placed. Aside from the placement differences, most of the microvias use the same aspect ratio.

1. Blind Microvias

This type of microvias is drilled to enable or pave the way for interconnections to start from the surface of the circuit board and go to the inner layer.

Worthy of mentioning is that the blind microvias is unlike the through-hole vias, which goes round the circuit board.

2. Buried Microvias

The buried microvias inherits some of the attributes of the blind microvias. These attributes include:

  • The aspect ratio stays low.
  • They span between two inner layers.

The best part of the buried microvias is the strong connection, which is enhanced by the filling of the copper. Any of the following can be used to fill the copper:

  • A combination of epoxy and copper resin.
  • Using a plating process with pure copper.

Buried microvias are also the best for reliability and this is tenable because of the spanning of a single layer.

3. Stacked Microvias

This is a type of microvias made with a combination of multiple blind and buried microvias. The goal is to enable the connections of the internal or inner layers. For the best results, the buried and blind microvias have to be stacked or placed on top of each other.

In addition to boosting the interconnection between the inner layers, the stacked microvias also helps the circuit board to have strengthened signal integrity.

4. Staggered Microvias

This is opposite of the stacked microvias, in the sense that it doesn’t have the microvias stacked or placed on top of each other. The second difference is that the staggered microvias consist of several buried microvias, unlike the stacked microvias that use a combination of buried and blind microvias.

For the microvias placement, they are not stacked, but are rather offset from one another, in successive layers.

5. Via-in-Pad Microvias

While the other microvias we discussed are the common types, the microvia in-pad is also another type. It is one of the best ways to miniaturize or reduce the sizes of Printed Circuit Boards (PCBs). It achieves this via the direct placement or drilling of the microvias holes on the copper solder of the component.

What You Must Know About Copper Filling in Microvias PCB

We have mentioned earlier that the copper in the microvias needs to be filled. Ever wondered the reason why that is so? And what might potentially happen if the copper is not filled?

Here are some of the things you must know about filling the microvias with copper:

1. Copper and Stress Levels

When the microvias is stressed, that is when you have issues of stress concentrated on the barrel region. When that happens, it wouldn’t be long before the microvias suffers a fractured neck.

Studies in this regard have uncovered the possibility of having increased stress levels in microvias with incomplete copper fillings.

This does not only reduce the microvias’ fatigue life, but also puts a hole in the design and development of the High Density Interconnect (HDI) PCBs. As a result, the HDI circuit boards would suffer a combination of incomplete fillings, voids and dimples during the copper plaiting process.

When to Fill the Microvias with Copper

Note that you may not be required to fill the microvias with copper, if there is no need to do so. However, special considerations are given to the following:

  • Buried Microvias: you should fill the buried microvias with copper, especially if it is not stacked.
  • Blind Microvias: it is common not to fill the blind microvias with copper. While this is typical during the era of microvia fabrication and implementation, you may want to consider otherwise. This time, it is possible to fill the blind microvia with copper via the standard copper process. This should be the case if the blind microvias will be used in-pad.

The Benefits of Working with Microvias

Despite the differences in terms of placement, there are a couple of advantages to using microvias. Here are some of those benefits:

1. Microvias have Shorter Trace Lengths

A shorter pathway also means that the speed of transmitting signals will be faster. Such is the case with the shorter trace lengths of microvias. When compared to the lengthy trace lengths of the standards vias, the microvias takes advantage of the shorter diameters to improve the FR capability of the circuit boards.

2. Space-Saving Feature

Due to the smaller size, microvias can fit into the smallest of spaces. Coupled with the fact that it makes interconnections in denser spaces, it is impressive to see more real estate space miniaturized in the PCB.

3. EMI Mitigations

Electromagnetic Interference (EMI) is one factor that negatively impacts the performance of circuit boards. When other channels and pathways are interfering or interrupting signal flow, it leads to EMI. Factors like noise coming from nearby radios/televisions, and other devices that could serve as a means of radiations and interruptions.

However, it is possible to have less susceptibility or exposure to EMI when working with microvias. Due to the smaller parasitic capacitance and inductance, the microvias can now be placed or packed into denser spaces – even if it means placing it closer to the components.

Despite being packed closer or together, the microvias is not exposed to some of the EMI factors, such as noise coupling and crosstalking.

4. Reduced Risks of Manufacturing Defects

Defects or errors arising from the design of Printed Circuit Boards (PCBs) are now reduced, thanks to the use of microvias.

How this reduction comes about is due to the use of lasers or the use of the laser-drilling method to create or insert the microvias into the circuit board. This helps reduce the residue deposition on the surface, while preventing some of the other issues arising due to the fabrication of circuit boards.


The use of microvias, no matter the type, helps to improve signal integrity, shorten the trace lengths, prevent manufacturing defects and save more space in the PCB.

We at Hillman Curtis help you to optimize the microvias in line with the future-oriented applications, especially now that circuit boards are used for manufacturing modern devices across different industries.

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