Chapter 3
Setting Up a Design
3-2
ni.com
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The other method typically uses a layered pair as a core to which single
layers of copper foil are added to build up the board. Prepreg is also
used to bond the layers. Build-up layers are usually added in equal
numbers to the top and bottom of the core to prevent warping of the
final product.
A via is a plated through-hole in a printed circuit board used to connect two
or more layers, as well as the top and bottom surfaces of the board.
•
Blind via
—Any via that connects the top or bottom layer of a board to
one of the internal layers.
•
Buried via
—Any via that connects internal layers.
•
Normal through-hole via
—Any via that connects all layers (top,
bottom, and internal).
•
Micro via
—A via that is less than 5 mils in diameter, that connects a
maximum of two build-up layers only.
The lamination sequence used determines the acceptable layer
combinations for placing blind and buried vias or microvias. For example,
if all layers are layered pairs then blind vias can only be placed between an
outer layer and completely through a layered pair (see diagram for an
example). Once the lamination sequence is determined, Ultiboard
calculates the acceptable layer combinations for blind and buried vias or
micro vias. You then choose which ones to use in your design from these
possible combinations.
The figure below shows a cross-section of a multi-layer PCB.
The number of copper layers in a board can be set in either the
Board Wizard
or in the
PCB Properties
dialog box. Refer to the
section and the
section of Chapter 1,
, for more information.
