Honestly, it mainly refers to the function of vias. As you probably know, vias are mainly used to connect lines of each layer. That’s to say, after metallizing treatment, the circuit boards on both sides of vias are connected together.
For example, in the multilayer circuit board, for the same vias, if certain layers need to be connected, then vias on these layers is going to be metallized; But what if the layer of lines do not need to be connected? Correspondingly, the vias of the layer won’t be metallized.
