Sequential Build Up
A “Sequential Build Up” may be necessary for pcbs with high density(HDI). This technology consists in adding layers at different times(sequential) to already partially made multilayers.
A PCB with buried vias is a perfect example. First of all we need to prepare the innerlayers that need to be plated. In a next “sequence” extra layers are added which need another through-hole plating. These “sequences” can be repeated several times.
Besides the use of buried vias, these boards usually contain blind vias which are drilled until a defined layer.