Printed circuit boards

When you’re told that your printed circuit board designs will require microvias to provide layer to layer high-density interconnects and the use of multiple features on a single board, you may be wondering what these circuit board features are and how they work to improve functionality on small electronic boards. Providing interconnects between layers of printed circuit boards, microvias make it easier to improve the board’s ability to run multiple features without increasing the overall area of the board. Here’s a quick look at what microvias are, how they work, how reliable they are, and similar concerns.

As technology has advanced, it is driving component and PCB formats smaller, to the point that the phone in your pocket has more computing power than the IBM mainframes that took up entire rooms at NASA used to calculate orbital projections. However, as technology has provided more power in smaller form factors, it’s changed some of the requirements for production, requirements that you need to stay on top of to ensure you get the best possible results from your printed circuit boards.

What are considered microvias?

The technical definition of a microvia under IPC standards is a hole that has an aspect ratio of 1:1 or less, meaning the ratio of the diameter to the depth, with the depth not to exceed 0.25 millimeters in large microvias, with some tiny microvias as small as 15 micrometers, which is why they are most commonly cut using a laser. As technology has become smaller while becoming more powerful, this means that circuit boards have evolved from a single board to multiple layer boards with microvias connecting printed circuit layers so that multiple functions can be operating at the same time.

This process has four steps:

• including layer lamination
• via formation
• via metallization
• via filling.

Via filling can be handled using different materials, including epoxy resin, non-conductive or conductive material, electroplated copper and similar materials. Microvias within the layers of the circuit board must be filled, while those on the surface may be left open, depending on your needs.

What are microvias in PCB?

Modern printed circuit boards (PCB) that use microvias typically are printed on both sides, which are then layered to create a sandwich of processing power. The microvias connect the different layers of the circuit boards. However, they do not connect within a single layer. In other words, they connect the horizontal aspects of a single printed circuit board layer to the horizontal aspects of another single printed circuit layer vertically within the same PCB, rather than following the circuit horizontally.

Learn more about microvias in PCB:

•  Laser Drilling Microvias in PCBs

Microvia Reliability

Because the reliability of the entire assembly is vital to its performance and the device’s overall reliability, microvia reliability is one of the constraints to large-scale adoption. There are many factors that can impact microvia reliability, including the dielectric properties of the material used, geometry parameters of the microvia and production parameters in the manufacturing facility.

Other factors that can impact the microvia’s reliability over time include the stress and strain loads in single-layer microvias, the estimated microvia fatigue life and thermomechanical stress, which can project the point of failure in these important features. These can be impacted by the trace or conductor thickness, the dielectric layers around the microvia, ductility coefficient of the conductor and strain concentration factor.

Microvia Voiding

There are some challenges to be considered in producing printed circuit boards with microvias, especially the issue of microvia voiding. This happens when there is an incomplete filling of the microvia, causing a void to be formed. This void can cause increased stress in the microvia which, in turn, lowers the overall useful lifespan of the printed circuit board.

Because it can prevent the board from operating properly, it can have a significant impact on the board’s reliability over time. Though studies have shown that small spherical voids can slightly increase the overall reliability and lifespan of the printed circuit board, larger ones can drastically reduce reliability and lifespan, to the point of causing a failure in quality assurance testing.

In Conclusion

Microvias are an excellent tool when creating multi-layer printed circuit boards, allowing your company to keep up with advancements in technology while reducing the size of your circuit boards. However, they must be processed carefully during the filling and metallization process to ensure that voids and poor plating adhesion are prevented in manufacturing. Working with a precision laser microvia drilling company can help improve your odds of success.

More in our Microvia Drilling Informative Article Series

Micron Laser specializes in Microvia Laser Drilling Services

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