By Microvias Be Filled With Non-Conductive Materials
The use of microvias in high-density circuit boards (PCBs) provides a valuable connection point for electrical signals between layers. They also enable a smaller form factor and lower weight, which can help with component positioning and layouts. However, these high-performance connections require careful consideration during design and fabrication. Choosing the right materials and understanding their limitations and potential problems can ensure a successful result.
The most common method of establishing an electrical connection through a microvia is to fill it with copper. Copper is a highly conductive material that provides superior performance and reliability. It also has a low thermal resistance and can tolerate a wide temperature range.
During the manufacturing process, microvias are filled and then plated with copper to establish an effective connection between the layers of a PCB. The metallization process must be performed with great care to avoid manufacturing defects such as voids and uneven copper coverage of the via walls.
Can Microvias Be Filled With Non-Conductive Materials?
In order to avoid these defects, a precise aspect ratio must be maintained. For a microvia, the ratio of its depth to its diameter must be no more than 1:1. Deviation from this ratio can cause problems during the drilling, metallization and plating processes.
Although a microvia’s aspect ratio limits its maximum diameter, the material used to fill the hole is far more critical to its functionality. The type of filling can have a significant impact on the quality of the electrical signal that can be transferred through it, as well as the thermal transfer capability.
At their core, microvias are essentially small holes drilled into printed circuit boards (PCBs) to establish electrical connections between different layers of the board. Unlike traditional vias, which are larger and penetrate through the entire thickness of the board, microvias are much smaller in diameter and typically connect only two adjacent layers. This allows for the creation of complex, high-density circuitry in a compact space.
The construction of microvias involves several precise manufacturing processes. Initially, a laser drilling or mechanical drilling technique is employed to create the tiny holes in the PCB substrate. Laser drilling is preferred for its precision and ability to create smaller diameter vias. After drilling, the vias are plated with conductive materials such as copper to establish electrical connectivity. The entire process demands meticulous attention to detail and sophisticated manufacturing equipment to ensure the accuracy and reliability of the microvias.
Conductive fills, such as silver and copper conductive epoxy, can significantly enhance the performance of a via. The metals in these fills wick away heat from components, which can reduce the risk of thermal stress and improve signal integrity. However, these fills are relatively expensive compared to non-conductive via plugging.
Another option is to fill a microvia with insulating materials, such as epoxy resins. This type of via fill is typically much more cost-effective than conductive copper filling, but it may not offer the same level of performance. In addition, insulating materials can cause additional problems during the manufacturing process, such as excess solder wicking up into the via holes during reflow and thermal stress accumulation around the plating edge of the via.