Key parameters / dielectric thicknesses

The most important parameter for microvias is the aspect ratio, the relationship between the hole diameter and the hole depth. Aspect ratio (AR) = Hole diameter (1) / Hole depth/length (2).

Two standard prepreg types are used as the dielectric material (5):
Prepreg type 1080:
60 – 65 µm dielectric layer thickness(5), end of hole diameter(3) = 100 µm 
Prepreg type 2116:
90 – 100 µm dielectric layer thickness(5), end of hole diameter(3) = 120 µm

(1) Hole diameter
(2) Hole depth
(3) End of hole diameter
(4) Cu thickness (acc. to IPC 6012 min. 10 µm)
(5) Dielectric layer thickness

The maximum aspect ratio for microvias is 1 : 0.8