Microvia-Overview-Custom Design Circuit
Board Electronic Pcb
IPC standards define microvias as blind or buried vias with a diameter equal to or less than 150 μm. With the advent of smartphones and hand-held electronic devices, microvias have evolved from single-level to stacked microvias that cross over multiple HDI layers. Sequential build-up (SBU) technology is used to fabricate HDI boards. The HDI layers are usually built up from a traditionally manufactured double-sided core board or multilayer PCB. The HDI layers are built on both sides of the traditional PCB one by one with microvias. The SBU process consists of several steps: layer lamination, via formation, via metallization, and via filling. There are multiple choices of materials and/or technologies for each step.
Microvias can be filled with different materials and processes: (1) filled with epoxy resin (b-stage) during a sequential lamination process step; (2) filled with non-conductive or conductive material other than copper as a separate processing step; (3) plated closed with electroplated copper; (4) screen printed closed with a copper paste. Buried microvias are required to be filled, while blind microvias on the external layers usually do not have any fill requirements. A stacked microvia is usually filled with electroplated copper to make electrical interconnections between multiple HDI layers and provide structural support for the outer level(s) of the microvia or for a component mounted on the outermost copper pad.