When do we fill a via?

The vias on the PCB are used to connect two or more layers. It can be said as a hole drilled from top to bottom layers of the PCB with copper plated around it for conductivity. These are also called through hole vias. Micro vias are drilled using laser drill and through via by mechanical drill. There are blind and buried vias other than these through hole vias but that is a different subject. Vias generally are not filled. This is the cheapest option. But in some requirements, vias need to be filled and these vias are either conductive fill or non-conductive fill. Non-conductive fill types are generally filled with resin or solder mask. These are also called mask plugged vias. This type of filling is used in Via-in-Pad application. Solder Mask filling which is similar to screen printing is used for non-via-on-pad applications. One has to remember that blind vias and buried vias cannot have copper filling. Conductive filling provides thermal support and non-conductive filling prevents any solder or any contaminants from entering the via.