Filled vias require any special fabrication techniques
Vias are holes that connect circuit board layers, allowing electrical signals to travel across the surface of the PCB. Vias are normally plated with copper, but they can also be filled with other materials. The type of material used to fill the via determines its functionality. Some vias are simply filled with a non-conductive epoxy, while others can be copper-filled or silver-filled. These different types of vias serve different purposes and each have their own advantages and disadvantages.
The primary purpose of copper-filled vias is to provide a low-impedance connection between the layers of the PCB. However, a major drawback of copper-filled vias is that they are more expensive than other types of vias. To reduce costs, some manufacturers offer the option to plate a plug over the copper, thereby eliminating the need for the additional step of filling the via with copper.
In addition to preventing solder wicking, the MCV also serves as a structural support for a copper pad that is plated over the via in the case of a Via In Pad or VIPO processing. The main disadvantage of this type of via is that the MCV has a much higher thermal conductivity than the laminate, so it can cause heat to dissipate more rapidly from the chip to the drilled hole wall. This can lead to fractures between the pad and the hole wall.
Do filled vias require any special fabrication techniques?
The most common type of filled via is a conductive fill, usually either copper or silver epoxy. This improves the electrical signal transfer capability of the via while enhancing its thermal transfer capabilities. The metallic nature of the fill wicks heat away from the chip to the other side of the board where it can be more easily dissipated by a heat sink.
Both conductive and non-conductive via fills have their advantages and disadvantages. For example, a conductive fill is excellent for conducting heat, but it can increase the price of the printed circuit board because copper has a higher cost than the resin that forms the laminate.
In general, it is recommended that the designer use a non-conductive fill for all standard PCBs unless there are specific design requirements that require a conductive via fill. If this is the case, the manufacturer should be notified at an early stage to ensure that the proper Gerber files are submitted for fabrication.
The best way to avoid issues with a conductive filled via is to ensure that the appropriate IPC-4761 type is specified. This will make it easy for both the designer and manufacturer to understand what is required in terms of via diameter and depth of fill. For instance, a conductive filled via needs to be specified as an IPC-4761 type “-b” and a non-conductive filled via as a “-a”. This will make it clear that the requirement is to have a minimum of 70% of the via hole filled with copper.