Micro vias are blind via holes with a diameter below 0.15 mm. These can be stacked, staggered, stepped, blind, buried and filled in several ways. In general they enhance signal integrity by having lower parasitic values and do not leave unwanted stubs like normal PTH vias. They take up less real-estate on the PCB and allow for vias to be placed in smaller pads. This in turn leaves room for more components and more connections on fewer layers. When choosing micro via structure it is important to know the strength and weakness of the technology. For instance, a skip micro via can be produced by making one “deep micro via” past the skipped layer. This structure is mechanically less stable than stacking a via on top of a copper filled via without connection to the skipped layer.
Micro vias can be drilled using CNC drilling machines, plasma etching machines, or laser drilling machines. For highest accuracy and reliability, Azitech recommends that micro vias should be drilled using a laser drilling machine. The aspect ratio of micro vias can be up to 0.7:1 or 1:1. Aspect ratio with 1:1 can be manufactured as prototypes at our special prototype suppliers in Europe. For mass production in Asia the maximum aspect ratio should not be higher than 0.7:1. For examples of high density interconnect stack ups and more use of micro vias, please visit our design center.
|Min. hole size||100 µm||100 µm|
|Min. capture PAD size||250 µm||250 µm|
|Min. target PAD size||250 µm||250 µm|
|Preferred micro via prepregs**|
|Min. plated thickness (micro vias)||10 µm||10 µm|
|FIlled micro via planarity||± 5 µm||± 5 µm|
** Contact Azitech.