Blind Microvias
A via, or plated through hole (PTH), is an access point connecting one layer of the PCB to another. It provides conductivity through copper plating or filling the hole with a conductive material. Typically, a via is found on the surface of the board, though it can also be buried in one or more layers within the PCB. The term microvia refers to a via that is smaller than standard PTHs, which can be 0.006 inches in diameter or less. These tiny holes are used in high-density interconnect printed circuit boards (HDI PCBs) to reduce cost and size, while still providing reliable signal transmission.
There are two types of microvias, blind and buried. Blind microvias start on the surface layer and end in one or more inner layers, while buried microvias exist between the inner layers of the board and do not reach any of the surface layers.
Both types of microvias save space, which cuts costs on the overall PCB and makes it possible to produce electronic devices that are much smaller and more compact than previous generations of products. However, there are some design restrictions to consider when using microvias.
What Are Blind Microvias?
In order for a microvia to function properly, it must be filled with copper. When a via is empty, there are several potential problems that could occur, such as stress concentration along the wall of the via or improper contact between the traces. This may result in failure of the PCB, reduced performance, or additional manufacturing steps.
To avoid these issues, the via must be plated with copper using the bottom-up process, which involves depositing copper preferentially onto the captured pad and then filling it with a conductive material such as gold or silver. The deposited copper must be even to avoid uneven via wall thickness, which can cause the PCB to fail to meet specification or experience excessive failures during operation.
A good PCB fabrication shop will know how to create these vias in the most efficient way possible. They will be able to minimize the number of thermal press cycles required to make them, which in turn will lower the cost of the finished product. In addition, they will be able to use a high-density layer stack to make sure that the microvias are spaced appropriately for the maximum amount of signal transmission possible.
The use of buried and blind microvias is essential for creating HDI PCBs, which are more compact than traditional PCBs and have increased circuitry density for improved functionality and reliability. This technology is already widely used in consumer electronics, such as laptops, cellphones, and digital cameras, but it can also be found in many other modern technologies.
To make the best use of buried and blind microvias, designers must keep in mind that these structures require more manufacturing steps than standard PTHs, and that they should be used only when necessary. If they are overused, they can add to the cost and complexity of the board, while reducing its reliability and performance. By carefully considering the advantages and limitations of these specialized vias, designers can design a high-performance and high-density PCB that meets the requirements of today’s electronic products.