ding Blind Vias in multilayer
printed boards.
1)  Why would someone want to use them?
2)  If used are they always filled?
3)  When does the filling operation take place?
4)  Are they required to be capped by plating 
    or solder mask?

I am looking at a lot of multilayers with blind vias and
need some help in understanding the manuf process.

Thanks,
Susan Mansilla
Robisan Laboratory