Blind and buried vias rather than through-hole vias are more effective for
minimizing EMI/RFI and maintaining high signal integrity, especially in
high-speed boards. For instance, in the through-hole approach, a signal may go
from the top layer to layer three, but if the hole goes all the way to a bottom
layer, such as layer 12, then a stub is created. This stub is the portion of the
through-hole via not used for signal transmission. In effect, the stub serves as
an antenna that creates added noise. Blind vias are used to transmit signals
between layers and provide exact termination at the exact layer. For example, a
blind via can go from layer one to layer three and terminate at layer three,
even if that PCB has 12 or more layers. |
