Role of Microvias in PCB Fabrication
The tiny vias known as microvias play important roles in connecting PCB layers, ensuring the smooth transmission of electrical signals and power. They are an essential feature in the high-density interconnection (HDI) trends that are reshaping electronic devices. Moreover, they provide an opportunity to optimize space and improve performance by reducing signal loss and improving impedance control in signal traces. It is important for PCB designers to understand these trends and the role of microvias in order to design circuit boards that meet current and future device demands.
The function of a microvia is similar to that of a regular through-hole via, except that it can also act as an alternative to routing through the top and bottom layers of a PCB. By providing a way to skip one layer and connect to other layers without the need for soldering, microvias allow manufacturers to produce thinner and more compact electronic products.
However, the small size of microvias can introduce manufacturing challenges and lead to a host of problems that may undermine the quality of the connections they provide. To avoid these issues, a fabricator should ensure that they use the best possible materials and plating techniques. For example, copper is an ideal material for conductive filling, as it offers excellent thermal and electrical properties. However, it is critical to note that not all copper is created equal. In fact, low-quality copper can cause defects and voids that compromise the integrity of the connections.
The Role of Microvias in PCB Fabrication
In addition to the need for proper copper quality, it is also vital that a fabricator employ the right drilling and plating techniques to ensure that microvias are properly filled. This is because even a small void can negatively impact the performance of a PCB. A void can affect the electrical conductivity and thermal expansion of a microvia, thereby decreasing the reliability of the connections it provides.
To prevent such voids, a fabricator should make sure to use pulse plating in the body of the microvia. This process fills the interior of a microvia with solid copper, removing any voids. Additionally, a fabricator should use additives during the plating process to ensure that the copper is properly bonded to the surrounding substrate. This will prevent the microvia from becoming deformed due to the stress of the plating process.
Finally, a fabricator should also be able to handle the heat that can be generated during the microvia plating process. This is especially important for high-frequency designs that rely on plated through holes to transmit signals. The thickness of a microvia’s plating can significantly affect its performance, so a fabricator should be able to achieve a high level of accuracy in this regard.
Microvias can be stacked or staggered to increase the density of a PCB. Staggered microvias are typically tracked away from buried microvia holes to minimize failure rates at the interface between stacked and buried microvias. In general, a buried microvia should be no deeper than 1:1 in relation to its diameter, as a deeper ratio can result in poor contact and failure.