Microvia staggered on top of buried via: optimal distance?

[JFDuval]

Hi, I'm designing a 6-layer PCB with blind vias going from L1 to L5, and L2 to L6. One option the fabricator is offering is to use a microvia combined with a buried via to create the blind via. I understand that staggering the holes is important for reliability. How much center to center distance is recommended? The holes are 8 mil. Reference materials, links, and whitepapers would be greatly appreciated! Thanks, JF

 

[JFDuval]

Hi, I'm designing a 6-layer PCB with blind vias going from L1 to L5, and L2 to L6. One option the fabricator is offering is to stack microvias. Is this more reliable than using one microvia and a staggered buried via? The holes are 8 mil. I found whitepapers on the reliability of 2, 3 and 4 stacked microvias, but nothing comparing 4 stacked microvias and one micro combined with a L2-L5 buried via. Reference materials, links, and whitepapers would be greatly appreciated! Thanks, JF

 

[senilicus]

Have a look at the attached file.